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• 1. [Article] The response of atmospheric nitrous oxide to climate variations during the last glacial period

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the American ...

  Citation × Citation Citation Abstract Copy Title: The response of atmospheric nitrous oxide to climate variations during the last glacial period Author: Schwander, Jakob, Baumgartner, Matthias, Eicher, Olivier, Stocker, Thomas F., Schilt, Adrian, Chappellaz, Jérôme, Fischer, Hubertus To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Title: The response of atmospheric nitrous oxide to climate variations during the last glacial period Author: Schwander, Jakob, Baumgartner, Matthias, Eicher, Olivier, Stocker, Thomas F., Schilt, Adrian, Chappellaz, Jérôme, Fischer, Hubertus To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Close

• 2. [Article] Abrupt change in atmospheric CO₂ during the last ice age

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/.

  Citation × Citation Citation Abstract Copy Title: Abrupt change in atmospheric CO₂ during the last ice age Author: Brook, Edward J., Kreutz, Karl, Ahn, Jinho, Schmittner, Andreas This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Title: Abrupt change in atmospheric CO₂ during the last ice age Author: Brook, Edward J., Kreutz, Karl, Ahn, Jinho, Schmittner, Andreas This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Close

• 3. [Article] A 37,000-year record of paleomagnetic and environmental magnetic variability from Burial Lake, Arctic Alaska

  Burial Lake sediments from the Noatak Basin in the northwest Brooks Range of Arctic Alaska (68.43°N, 159.17°W, 21.5 m water depth) provide the oldest continuous lacustrine record of paleo-environmental ...

  Citation × Citation Citation Abstract Copy Title: A 37,000-year record of paleomagnetic and environmental magnetic variability from Burial Lake, Arctic Alaska Author: Dorfman, Jason Michael Burial Lake sediments from the Noatak Basin in the northwest Brooks Range of Arctic Alaska (68.43°N, 159.17°W, 21.5 m water depth) provide the oldest continuous lacustrine record of paleo-environmental change and paleomagnetic secular variation (PSV) in eastern Beringia. A precise radiocarbon chronology, determined through accelerator mass spectrometry (AMS) allows us to independently constrain the region's climatic and geomagnetic evolution over the last ~37,000 years. Progressive alternating field (AF) demagnetization of u-channel samples and additionally acquired physical, geochemical, and rock-magnetic datasets, reveal three distinct lithologic subunits associated with the last glacial period (37.2 - 19.4 ka), the deglacial transition (19.4 - 9.8 ka), and the Holocene (9.8 ka - present). Rock magnetic variability suggests changes in sediment provenance associated with the transition from glacial to interglacial conditions. This is interpreted to result from a variable flux of aeolian derived sediment, and is supported by complimentary internal proxy data from Burial Lake. Other regional paleoclimate data, various glacial chronologies for the Brooks Range, and a relative sea level reconstruction facilitate a discussion of possible local, widespread, and far-field sources of dust, and the time-dependency of potential forcing mechanisms governing its production, availability, transport, and deposition. Results indicate an overall reduction in dust input from the glacial period to the Holocene that is largely attributed to increases in terrestrial and aquatic productivity, warming, and moisture availability, which limited widespread landscape deflation and production of dust. Subaerial continental shelves may have provided significant far-field sources of dust to interior Alaska during the glacial period, that were shut off by sea level inundation following the Last Glacial Maximum (LGM; 19 - 26.5 ka), further contributing to diminishing dust emissions. While glacial activity in the Brooks Range may provide local revenue of dust, activation of those deposits and timing of deposition in Burial Lake often appears to be more directly linked with general aridity, lack of vegetative cover, and increased windiness, rather than glacial advances or retreats. Despite this lithologic complexity, we isolate a stable, single-component characteristic remanent magnetization, carried predominately by low-coercivity (titano)magnetite in the pseudo single-domain (PSD) to multi-domain (MD) magnetic grain size range. We reconstruct directional paleomagnetic secular variation (PSV) over the full length of the record, and relative paleointensity (RPI) for the last ~14,700 years, which are consistent with available regional PSV records and continuous spherical harmonic model outputs. We observe only small deviations from geocentric axial dipole (GAD) predictions during the Holocene, while larger amplitude directional features are prevalent before 10 ka, and inclinations lay significantly shallower than GAD. While this may be related to lithology and the sediment magnetic acquisition process, regional records (including those derived from lava flows) indicate similar Holocene-Pleistocene discrepancies. Following on the "eccentric dipole" hypothesis, subdued secular variation and GAD-like behavior in the Pacific appears confined to the Holocene high-intensity state, showing greater variability as Pleistocene field strength diminishes, and/or the dipole axis is shifted away from the Pacific hemisphere. Long period trends in PSV from in the Alaskan Arctic are also similar in character to far-field sites (e.g., Hawaii and Siberia), suggesting large-scale coherent core-fluid flow regimes, expressed over surface geographical extents >5,000 km, and spanning Holocene-Pleistocene time intervals. The well-dated Burial Lake record fills a significant data gap in the growing Holocene paleomagnetic database, while allowing us to extend our understanding of PSV beyond the Holocene and into the Pleistocene, and continue the development of regional stratigraphic dating curves. Title: A 37,000-year record of paleomagnetic and environmental magnetic variability from Burial Lake, Arctic Alaska Author: Dorfman, Jason Michael Burial Lake sediments from the Noatak Basin in the northwest Brooks Range of Arctic Alaska (68.43°N, 159.17°W, 21.5 m water depth) provide the oldest continuous lacustrine record of paleo-environmental change and paleomagnetic secular variation (PSV) in eastern Beringia. A precise radiocarbon chronology, determined through accelerator mass spectrometry (AMS) allows us to independently constrain the region's climatic and geomagnetic evolution over the last ~37,000 years. Progressive alternating field (AF) demagnetization of u-channel samples and additionally acquired physical, geochemical, and rock-magnetic datasets, reveal three distinct lithologic subunits associated with the last glacial period (37.2 - 19.4 ka), the deglacial transition (19.4 - 9.8 ka), and the Holocene (9.8 ka - present). Rock magnetic variability suggests changes in sediment provenance associated with the transition from glacial to interglacial conditions. This is interpreted to result from a variable flux of aeolian derived sediment, and is supported by complimentary internal proxy data from Burial Lake. Other regional paleoclimate data, various glacial chronologies for the Brooks Range, and a relative sea level reconstruction facilitate a discussion of possible local, widespread, and far-field sources of dust, and the time-dependency of potential forcing mechanisms governing its production, availability, transport, and deposition. Results indicate an overall reduction in dust input from the glacial period to the Holocene that is largely attributed to increases in terrestrial and aquatic productivity, warming, and moisture availability, which limited widespread landscape deflation and production of dust. Subaerial continental shelves may have provided significant far-field sources of dust to interior Alaska during the glacial period, that were shut off by sea level inundation following the Last Glacial Maximum (LGM; 19 - 26.5 ka), further contributing to diminishing dust emissions. While glacial activity in the Brooks Range may provide local revenue of dust, activation of those deposits and timing of deposition in Burial Lake often appears to be more directly linked with general aridity, lack of vegetative cover, and increased windiness, rather than glacial advances or retreats. Despite this lithologic complexity, we isolate a stable, single-component characteristic remanent magnetization, carried predominately by low-coercivity (titano)magnetite in the pseudo single-domain (PSD) to multi-domain (MD) magnetic grain size range. We reconstruct directional paleomagnetic secular variation (PSV) over the full length of the record, and relative paleointensity (RPI) for the last ~14,700 years, which are consistent with available regional PSV records and continuous spherical harmonic model outputs. We observe only small deviations from geocentric axial dipole (GAD) predictions during the Holocene, while larger amplitude directional features are prevalent before 10 ka, and inclinations lay significantly shallower than GAD. While this may be related to lithology and the sediment magnetic acquisition process, regional records (including those derived from lava flows) indicate similar Holocene-Pleistocene discrepancies. Following on the "eccentric dipole" hypothesis, subdued secular variation and GAD-like behavior in the Pacific appears confined to the Holocene high-intensity state, showing greater variability as Pleistocene field strength diminishes, and/or the dipole axis is shifted away from the Pacific hemisphere. Long period trends in PSV from in the Alaskan Arctic are also similar in character to far-field sites (e.g., Hawaii and Siberia), suggesting large-scale coherent core-fluid flow regimes, expressed over surface geographical extents >5,000 km, and spanning Holocene-Pleistocene time intervals. The well-dated Burial Lake record fills a significant data gap in the growing Holocene paleomagnetic database, while allowing us to extend our understanding of PSV beyond the Holocene and into the Pleistocene, and continue the development of regional stratigraphic dating curves. Close

• 4. [Article] Impact of the Ocean’s Overturning Circulation on Atmospheric CO2

  A coupled climate-carbon cycle model and ice core CO2 data from the last glacial period are used to explore the impact of changes in ocean circulation on atmospheric CO2 concentrations on millennial time ...

  Citation × Citation Citation Abstract Copy Title: Impact of the Ocean’s Overturning Circulation on Atmospheric CO2 Author: Brook, Edward J., Schmittner, Andreas, Ahn, Jinho A coupled climate-carbon cycle model and ice core CO2 data from the last glacial period are used to explore the impact of changes in ocean circulation on atmospheric CO2 concentrations on millennial time scales. In the model, stronger wind driven circulation increases atmospheric CO2. Changes in the buoyancy driven deep overturning in the Atlantic affect atmospheric CO2 only indirectly through their effect on Southern Ocean stratification. In simulations with an abrupt and complete shutdown of the Atlantic overturning, stratification in the Southern Ocean decreases due to salinification of surface waters and freshening of the deep sea. Deeper mixed layers and steeper isopycnals lead to outgassing of CO2 in the Southern Ocean and hence gradually increasing atmospheric CO2 concentrations on a multi-millennial time scale. The rise in CO2 terminates at the time of rapid resumption of deep water formation and warming in the North Atlantic, and CO2 levels subsequently gradually decrease. These model responses and a strong correlation between simulated atmospheric CO2 and Antarctic surface air temperatures with little or no time lag are consistent with newly synchronized ice core data from the last ice age. Sensitivity experiments reveal that the amplitude of the response of atmospheric CO2 is sensitive to the model background climatic state and decreases in a colder climate owing to smaller changes in the overturning. Title: Impact of the Ocean’s Overturning Circulation on Atmospheric CO2 Author: Brook, Edward J., Schmittner, Andreas, Ahn, Jinho A coupled climate-carbon cycle model and ice core CO2 data from the last glacial period are used to explore the impact of changes in ocean circulation on atmospheric CO2 concentrations on millennial time scales. In the model, stronger wind driven circulation increases atmospheric CO2. Changes in the buoyancy driven deep overturning in the Atlantic affect atmospheric CO2 only indirectly through their effect on Southern Ocean stratification. In simulations with an abrupt and complete shutdown of the Atlantic overturning, stratification in the Southern Ocean decreases due to salinification of surface waters and freshening of the deep sea. Deeper mixed layers and steeper isopycnals lead to outgassing of CO2 in the Southern Ocean and hence gradually increasing atmospheric CO2 concentrations on a multi-millennial time scale. The rise in CO2 terminates at the time of rapid resumption of deep water formation and warming in the North Atlantic, and CO2 levels subsequently gradually decrease. These model responses and a strong correlation between simulated atmospheric CO2 and Antarctic surface air temperatures with little or no time lag are consistent with newly synchronized ice core data from the last ice age. Sensitivity experiments reveal that the amplitude of the response of atmospheric CO2 is sensitive to the model background climatic state and decreases in a colder climate owing to smaller changes in the overturning. Close

• 5. [Article] Physical-biological interactions in the Southern Ocean

  Physical-biological interactions in the Southern Ocean were investigated using remote sensing data from several different satellite sensors. Satellite sea surface temperature data were used to study the ...

  Citation × Citation Citation Abstract Copy Title: Physical-biological interactions in the Southern Ocean Author: Moore, Jefferson Keith Physical-biological interactions in the Southern Ocean were investigated using remote sensing data from several different satellite sensors. Satellite sea surface temperature data were used to study the dynamics of the Antarctic Polar Front (PF). Satellite ocean color data were used to estimate surface chlorophyll concentrations and their relation to various physical forcings within the Southern Ocean. A detailed study of phytoplankton blooms at the Antarctic Polar Front revealed that elevated chlorophyll concentrations (phytoplankton blooms) occur most often in areas where the PF interacts with large topographic features within the Southern Ocean. The physical dynamics of the PF are strongly influenced by the topography, and in turn strongly influence phytoplankton bloom dynamics. The analysis of satellite data from the modern Southern Ocean indicates that phytoplankton are limited by the availability of the micronutrient iron in most areas. This iron-limitation implies that the elevated iron inputs during glacial periods would have led to increased phytoplankton primary and export production and a stronger sink for atmospheric CO₂ in the Southern Ocean. Title: Physical-biological interactions in the Southern Ocean Author: Moore, Jefferson Keith Physical-biological interactions in the Southern Ocean were investigated using remote sensing data from several different satellite sensors. Satellite sea surface temperature data were used to study the dynamics of the Antarctic Polar Front (PF). Satellite ocean color data were used to estimate surface chlorophyll concentrations and their relation to various physical forcings within the Southern Ocean. A detailed study of phytoplankton blooms at the Antarctic Polar Front revealed that elevated chlorophyll concentrations (phytoplankton blooms) occur most often in areas where the PF interacts with large topographic features within the Southern Ocean. The physical dynamics of the PF are strongly influenced by the topography, and in turn strongly influence phytoplankton bloom dynamics. The analysis of satellite data from the modern Southern Ocean indicates that phytoplankton are limited by the availability of the micronutrient iron in most areas. This iron-limitation implies that the elevated iron inputs during glacial periods would have led to increased phytoplankton primary and export production and a stronger sink for atmospheric CO₂ in the Southern Ocean. Close

• 6. [Article] Atmospheric CO₂ and climate from 65 to 30 ka B.P.

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/.

  Citation × Citation Citation Abstract Copy Title: Atmospheric CO₂ and climate from 65 to 30 ka B.P. Author: Ahn, Jinho, Brook, Edward J. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Title: Atmospheric CO₂ and climate from 65 to 30 ka B.P. Author: Ahn, Jinho, Brook, Edward J. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Close

• 7. [Article] Terrigenous Fe input and biogenic sedimentation in the glacial and interglacial equatorial Pacific Ocean

  Many ocean regions important to the global carbon budget, including the equatorial Pacific Ocean, have low chlorophyll concentrations despite high levels of conventional nutrients. Iron may instead by ...

  Citation × Citation Citation Abstract Copy Title: Terrigenous Fe input and biogenic sedimentation in the glacial and interglacial equatorial Pacific Ocean Author: Murray, D. W., Leinen, M., Murray, R. W., Knowlton, C. W., Mix, Alan C. Many ocean regions important to the global carbon budget, including the equatorial Pacific Ocean, have low chlorophyll concentrations despite high levels of conventional nutrients. Iron may instead by the limiting nutrient, and elevated input of terrigenous Fe during windy glacial episodes has been hypothesized to stimulate oceanic productivity through time and thus regular the oceanic and atmospheric CO2 balance. To test whether particulate Fe input is related to the accumulation of biogenic matter in one important low chlorophyll-high nutrient area, that is, the equatorial Pacific Ocean, we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial-interglacial cycles (~600,000 years). Our data set includes new chemical data on total Fe, terrigenous, and biogenic components in three cores as well as previously published mineralogic records of eolian input to the region. Chemical, spectral, and stratigraphic analysis indicates that (1) terrigenous input to the region shows no consistent pattern of either glacial or interglacial maximz, (2) the accumulation of particulate Fe is closely related to the accumulation of terrigenous matter (linear r2=0.81-0.98), (3) there are no coherent spectral relationships between Fe input and glacial periodicity (i.e., δ18O) in any of the orbital frequency bands, (4) the linear and cross-spectral correlations between Fe or eolian input and CaCO3 concentration are most commonly the strongest observed relationships between Fe and any biogenic component, yet indicate a largely inverse pattern, with higher Fe being associated with low CaCO3, (5) there is no consistent linear r2 correlation or spectral coherence between the accumulation of Fe and that of CaCo3, Corg, or opal. Thus in total there is no relationship between terrigenous Fe input and sedimentary sequestering of carbon. Additionally, although we cannot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositional change, the Fe/Ti ratio (which monitors first-order mineralogic changes) records only slight variations that also are linearly and spectrally unrelated to glacial periodicity, the bulk Fe flux, and the accumulation of any biogenic component. Finally, we find that the paleoceanographic flux of Fe is several order-of-magnitudes larger than modern observations of eolian Fe input, suggesting that the long-term importance of Fe input by dust storms (which deliver Fe on the order of the sedimentary burial) may be underestimated. The removal of particulate terrigenous Fe from the recently discovered source within the Equatorial Undercurrent, however, remains unquantified and may also proved significant. Title: Terrigenous Fe input and biogenic sedimentation in the glacial and interglacial equatorial Pacific Ocean Author: Murray, D. W., Leinen, M., Murray, R. W., Knowlton, C. W., Mix, Alan C. Many ocean regions important to the global carbon budget, including the equatorial Pacific Ocean, have low chlorophyll concentrations despite high levels of conventional nutrients. Iron may instead by the limiting nutrient, and elevated input of terrigenous Fe during windy glacial episodes has been hypothesized to stimulate oceanic productivity through time and thus regular the oceanic and atmospheric CO2 balance. To test whether particulate Fe input is related to the accumulation of biogenic matter in one important low chlorophyll-high nutrient area, that is, the equatorial Pacific Ocean, we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial-interglacial cycles (~600,000 years). Our data set includes new chemical data on total Fe, terrigenous, and biogenic components in three cores as well as previously published mineralogic records of eolian input to the region. Chemical, spectral, and stratigraphic analysis indicates that (1) terrigenous input to the region shows no consistent pattern of either glacial or interglacial maximz, (2) the accumulation of particulate Fe is closely related to the accumulation of terrigenous matter (linear r2=0.81-0.98), (3) there are no coherent spectral relationships between Fe input and glacial periodicity (i.e., δ18O) in any of the orbital frequency bands, (4) the linear and cross-spectral correlations between Fe or eolian input and CaCO3 concentration are most commonly the strongest observed relationships between Fe and any biogenic component, yet indicate a largely inverse pattern, with higher Fe being associated with low CaCO3, (5) there is no consistent linear r2 correlation or spectral coherence between the accumulation of Fe and that of CaCo3, Corg, or opal. Thus in total there is no relationship between terrigenous Fe input and sedimentary sequestering of carbon. Additionally, although we cannot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositional change, the Fe/Ti ratio (which monitors first-order mineralogic changes) records only slight variations that also are linearly and spectrally unrelated to glacial periodicity, the bulk Fe flux, and the accumulation of any biogenic component. Finally, we find that the paleoceanographic flux of Fe is several order-of-magnitudes larger than modern observations of eolian Fe input, suggesting that the long-term importance of Fe input by dust storms (which deliver Fe on the order of the sedimentary burial) may be underestimated. The removal of particulate terrigenous Fe from the recently discovered source within the Equatorial Undercurrent, however, remains unquantified and may also proved significant. Close

• 8. [Article] Late Cenozoic Climate, Ice-sheet and Earth-surface Evolution Derived from Terrestrial and Marine Sedimentary Archives

  The goals of this dissertation are centered on understanding changes in Earth surface and climate systems through the use of geologic proxies as records of past changes in these systems. Specifically, ...

  Citation × Citation Citation Abstract Copy Title: Late Cenozoic Climate, Ice-sheet and Earth-surface Evolution Derived from Terrestrial and Marine Sedimentary Archives Author: Bill, Nicholas S. The goals of this dissertation are centered on understanding changes in Earth surface and climate systems through the use of geologic proxies as records of past changes in these systems. Specifically, this dissertation (1) establishes a new chronology for retreat of the Ross Sea sector of the West Antarctic Ice during the last deglaciation, (2) investigates the changes in the global climate system during the mid- Pleistocene transition, and (3) constrains the timing of surface uplift in Alaska, and the control that topography has on regional climate and the hydrologic cycle over the tectonic timescale. This dissertation establishes the timing of the last deglaciation of the Ross Sea Sector of the West Antarctic Ice Sheet (WAIS), addressing the question of whether grounded ice in the Ross Embayment deglaciated entirely in the Holocene or earlier. ¹⁰Be surface exposure dating of granitic glacial erratic boulders indicates that the onset of sustained retreat from the local Last Glacial Maximum started at 18.6 ± 1.1 ka, and that sustained retreat occurred into the middle Holocene. We attribute most of this retreat to temperature and radiative forcing of the ablation zone in McMurdo Sound with only the final stages of retreat possibly influenced by Holocene grounding line retreat. The mid-Pleistocene transition (MPT) represents a transition from predominantly 40-kyr climate cycles to predominantly 100-kyr cycles in the absence of any change in orbital forcing. Here I combine all existing records of SST (n=7) and δ¹³C (n=17) that span the entirety of the last 2 Ma and use principal component analysis to detect the shared global signal of these records across the MPT. I also develop stacks of ice volume, ocean basin-scale δ¹³C gradients and CO₂ reconstructions in an attempt to characterize the interaction between deep ocean circulation and climate change across the MPT. I find that the characteristic change in cyclicity of the MPT appears in SST, δ¹³C and ice-volume reconstructions. I interpret marine isotope stage (MIS) 23 (~900 ka) as a skipped interglacial that led to MIS 25- 21 as being the first 100-kyr period, potentially initiating the 100-kyr cycle during the rest of the Pleistocene. I also find that the largest global negative δ¹³C excursion in the Pleistocene occurred during the glacial periods MIS 24 and MIS 22. This excursion is likely related to a mean shift to a reduced glacial-period AMOC across the MPT that is observed in multiple AMOC strength reconstructions, and that I interpret as a key component of the MPT. The topography of southern Alaska has been shown to have likely experienced rapid exhumation during the early Pliocene stating ~5-6 Ma. Using δD measurements on OH- groups of clay minerals, I constrain the change in isotopic composition of paleo-meteoric water from the Miocene-Holocene in the interior of Alaska as a proxy for the surface uplift history of Alaskan topography via its control on the δD signal of surface water. My results suggest that there was rapid surface uplift of the several mountain ranges encompassing southern Alaska during the period from ~6.5-3 Ma. Title: Late Cenozoic Climate, Ice-sheet and Earth-surface Evolution Derived from Terrestrial and Marine Sedimentary Archives Author: Bill, Nicholas S. The goals of this dissertation are centered on understanding changes in Earth surface and climate systems through the use of geologic proxies as records of past changes in these systems. Specifically, this dissertation (1) establishes a new chronology for retreat of the Ross Sea sector of the West Antarctic Ice during the last deglaciation, (2) investigates the changes in the global climate system during the mid- Pleistocene transition, and (3) constrains the timing of surface uplift in Alaska, and the control that topography has on regional climate and the hydrologic cycle over the tectonic timescale. This dissertation establishes the timing of the last deglaciation of the Ross Sea Sector of the West Antarctic Ice Sheet (WAIS), addressing the question of whether grounded ice in the Ross Embayment deglaciated entirely in the Holocene or earlier. ¹⁰Be surface exposure dating of granitic glacial erratic boulders indicates that the onset of sustained retreat from the local Last Glacial Maximum started at 18.6 ± 1.1 ka, and that sustained retreat occurred into the middle Holocene. We attribute most of this retreat to temperature and radiative forcing of the ablation zone in McMurdo Sound with only the final stages of retreat possibly influenced by Holocene grounding line retreat. The mid-Pleistocene transition (MPT) represents a transition from predominantly 40-kyr climate cycles to predominantly 100-kyr cycles in the absence of any change in orbital forcing. Here I combine all existing records of SST (n=7) and δ¹³C (n=17) that span the entirety of the last 2 Ma and use principal component analysis to detect the shared global signal of these records across the MPT. I also develop stacks of ice volume, ocean basin-scale δ¹³C gradients and CO₂ reconstructions in an attempt to characterize the interaction between deep ocean circulation and climate change across the MPT. I find that the characteristic change in cyclicity of the MPT appears in SST, δ¹³C and ice-volume reconstructions. I interpret marine isotope stage (MIS) 23 (~900 ka) as a skipped interglacial that led to MIS 25- 21 as being the first 100-kyr period, potentially initiating the 100-kyr cycle during the rest of the Pleistocene. I also find that the largest global negative δ¹³C excursion in the Pleistocene occurred during the glacial periods MIS 24 and MIS 22. This excursion is likely related to a mean shift to a reduced glacial-period AMOC across the MPT that is observed in multiple AMOC strength reconstructions, and that I interpret as a key component of the MPT. The topography of southern Alaska has been shown to have likely experienced rapid exhumation during the early Pliocene stating ~5-6 Ma. Using δD measurements on OH- groups of clay minerals, I constrain the change in isotopic composition of paleo-meteoric water from the Miocene-Holocene in the interior of Alaska as a proxy for the surface uplift history of Alaskan topography via its control on the δD signal of surface water. My results suggest that there was rapid surface uplift of the several mountain ranges encompassing southern Alaska during the period from ~6.5-3 Ma. Close

• 9. [Article] Glacial greenhouse-gas fluctuations controlled by ocean circulation changes

  Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) varied strongly on millennial timescales during past glacial periods. Large and rapid ...

  Citation × Citation Citation Abstract Copy Title: Glacial greenhouse-gas fluctuations controlled by ocean circulation changes Author: Schmittner, Andreas, Galbraith, Eric D. Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N2O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO2. Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard–Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard–Oeschger temperature, as well as CO2 and N2O fluctuations. Despite significant changes in the land carbon inventory, CO2 variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N2O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO2 and N2O fluctuations on millennial timescales. Title: Glacial greenhouse-gas fluctuations controlled by ocean circulation changes Author: Schmittner, Andreas, Galbraith, Eric D. Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N2O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO2. Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard–Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard–Oeschger temperature, as well as CO2 and N2O fluctuations. Despite significant changes in the land carbon inventory, CO2 variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N2O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO2 and N2O fluctuations on millennial timescales. Close

• 10. [Article] Biogenic and terrigenous sedimetations at Ceara rise, western tropical Altantic, supports Pliocene - Pleistocene deep - water linkage between hemispheres

  Calcium carbonate percentages at five Ceara Rise sites were estimated at 1- to 2-k.y. intervals over the past 5 m.y., using reflectance spectroscopy and magnetic susceptibility proxies. From these estimates ...

  Citation × Citation Citation Abstract Copy Title: Biogenic and terrigenous sedimetations at Ceara rise, western tropical Altantic, supports Pliocene - Pleistocene deep - water linkage between hemispheres Author: Harris, Sara E., King, Terri, Mix, Alan C. Calcium carbonate percentages at five Ceara Rise sites were estimated at 1- to 2-k.y. intervals over the past 5 m.y., using reflectance spectroscopy and magnetic susceptibility proxies. From these estimates and detailed correlations between sites, gradients of calcite and terrigenous sediment accumulation rates in a depth transect of sites reveal variations in local climate and calcite dissolution related to deep-water masses. Relative to shallow sites on the southern Ceara Rise, accumulation rates of terrigenous sediments at deeper sites near the Amazon Fan were higher during glacial periods. Analogous variations in terrigenous sedimentation before the expansion of Northern Hemisphere ice sheets ~3 m.y. ago suggests that tropical climate cycles occurred independently of polar glaciation. Decreasing accumulation rates of calcite with increasing water depth reveal patterns of carbonate dissolution, which varied on orbital time-scales (10- 100 k.y. periods) throughout the Pliocene-Pleistocene. Maximum dissolution at deep relative to shallow sites occurred in the transition from interglacial to glacial conditions, and maximum preservation occurred during global warming, at all orbital periods. If the local dissolution gradient is linked to relative contributions of North Atlantic Deep Water and Antarctic Bottom Water, this phasing of events confirms a key prediction of SPECMAP that deep-water adjustments may translate climate changes between hemispheres. Dissolution and preservation events, however, may also reflect a transient response to a net flux of organic matter between the continents and the oceans during ice-age climate transitions. Title: Biogenic and terrigenous sedimetations at Ceara rise, western tropical Altantic, supports Pliocene - Pleistocene deep - water linkage between hemispheres Author: Harris, Sara E., King, Terri, Mix, Alan C. Calcium carbonate percentages at five Ceara Rise sites were estimated at 1- to 2-k.y. intervals over the past 5 m.y., using reflectance spectroscopy and magnetic susceptibility proxies. From these estimates and detailed correlations between sites, gradients of calcite and terrigenous sediment accumulation rates in a depth transect of sites reveal variations in local climate and calcite dissolution related to deep-water masses. Relative to shallow sites on the southern Ceara Rise, accumulation rates of terrigenous sediments at deeper sites near the Amazon Fan were higher during glacial periods. Analogous variations in terrigenous sedimentation before the expansion of Northern Hemisphere ice sheets ~3 m.y. ago suggests that tropical climate cycles occurred independently of polar glaciation. Decreasing accumulation rates of calcite with increasing water depth reveal patterns of carbonate dissolution, which varied on orbital time-scales (10- 100 k.y. periods) throughout the Pliocene-Pleistocene. Maximum dissolution at deep relative to shallow sites occurred in the transition from interglacial to glacial conditions, and maximum preservation occurred during global warming, at all orbital periods. If the local dissolution gradient is linked to relative contributions of North Atlantic Deep Water and Antarctic Bottom Water, this phasing of events confirms a key prediction of SPECMAP that deep-water adjustments may translate climate changes between hemispheres. Dissolution and preservation events, however, may also reflect a transient response to a net flux of organic matter between the continents and the oceans during ice-age climate transitions. Close

• 11. [Article] Southern Ocean control of glacial AMOC stability and Dansgaard-Oeschger interstadial duration

  Access to this item has been restricted by repository administrators at the request of the publisher until June 30, 2016.

  Citation × Citation Citation Abstract Copy Title: Southern Ocean control of glacial AMOC stability and Dansgaard-Oeschger interstadial duration Author: Buizert, Christo, Schmittner, Andreas Access to this item has been restricted by repository administrators at the request of the publisher until June 30, 2016. Title: Southern Ocean control of glacial AMOC stability and Dansgaard-Oeschger interstadial duration Author: Buizert, Christo, Schmittner, Andreas Access to this item has been restricted by repository administrators at the request of the publisher until June 30, 2016. Close

• 12. [Article] On the origin and timing of rapid changes in atmospheric methane during the Last Glacial Period

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gb/index.shtml.

  Citation × Citation Citation Abstract Copy Title: On the origin and timing of rapid changes in atmospheric methane during the Last Glacial Period Author: Steig, Eric J., Harder, Susan, Brook, Edward J., Severinghaus, Jeff, Sucher, Cara M. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gb/index.shtml. Title: On the origin and timing of rapid changes in atmospheric methane during the Last Glacial Period Author: Steig, Eric J., Harder, Susan, Brook, Edward J., Severinghaus, Jeff, Sucher, Cara M. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gb/index.shtml. Close

• 13. [Article] Model of late Pleistocene-Holocene variations in rate of sediment accumulation : Panama Basin, eastern equatorial Pacific

  The assumption of constant quartz accumulation for the deep-sea sediment core Y69-106P, taken in the Panama Basin, has been used to date the core and construct a sedimentation rate versus time curve for ...

  Citation × Citation Citation Abstract Copy Title: Model of late Pleistocene-Holocene variations in rate of sediment accumulation : Panama Basin, eastern equatorial Pacific Author: Pisias, Nicklas G. The assumption of constant quartz accumulation for the deep-sea sediment core Y69-106P, taken in the Panama Basin, has been used to date the core and construct a sedimentation rate versus time curve for it. Stratigraphic control for the calculated time scale includes three carbon-14 measurements, the extinction of the radiolarian Stylatractus universus, and correlation with oxygen isotope curves from other dated cores. The model sedimentation rates and sediment composition data allow the determination of sediment accumulation rates for calcium carbonate, opaline silica, and remaining "detritus". Fluctuations in calcium carbonate accumulation rates correlate closely with variations in oxygen isotope ratios in biogenous carbonate from two other equatorial Pacific sediment cores. High oxygen isotope ratios correlate with high calcium carbonate accumulation rates. Opaline silica accumulation rates reflect changes in the dominance of radiolarian fossil groups which can be related to surface circulation in the Panama Basin. The successive maxima in opal and calcium accumulation rates and the oxygen isotope ratios in Y69-106P suggest that at the end of the last glacial period, the rate of calcium carbonate dissolution increased in the Panama Basin first, to be followed by a decrease in the intensity of the eastern equatorial Pacific upwelling, and finally the volume of continental glaciers decreased. Spectral analysis of the rate of accumulation of calcium carbonate in Y69-106P and of the oxygen isotope record of core V28-238 indicate the presence of a 23,000 year periodicity. Analysis of opal accumulation rate suggest a 100,000 year periodicity. These two periodicities are found in fluctuations in the earth's orbital parameters. The eccentricity of the orbit fluctuates with an average period of 98,000 years and the precession of the equinoxes changes with a 22,000 year period. Title: Model of late Pleistocene-Holocene variations in rate of sediment accumulation : Panama Basin, eastern equatorial Pacific Author: Pisias, Nicklas G. The assumption of constant quartz accumulation for the deep-sea sediment core Y69-106P, taken in the Panama Basin, has been used to date the core and construct a sedimentation rate versus time curve for it. Stratigraphic control for the calculated time scale includes three carbon-14 measurements, the extinction of the radiolarian Stylatractus universus, and correlation with oxygen isotope curves from other dated cores. The model sedimentation rates and sediment composition data allow the determination of sediment accumulation rates for calcium carbonate, opaline silica, and remaining "detritus". Fluctuations in calcium carbonate accumulation rates correlate closely with variations in oxygen isotope ratios in biogenous carbonate from two other equatorial Pacific sediment cores. High oxygen isotope ratios correlate with high calcium carbonate accumulation rates. Opaline silica accumulation rates reflect changes in the dominance of radiolarian fossil groups which can be related to surface circulation in the Panama Basin. The successive maxima in opal and calcium accumulation rates and the oxygen isotope ratios in Y69-106P suggest that at the end of the last glacial period, the rate of calcium carbonate dissolution increased in the Panama Basin first, to be followed by a decrease in the intensity of the eastern equatorial Pacific upwelling, and finally the volume of continental glaciers decreased. Spectral analysis of the rate of accumulation of calcium carbonate in Y69-106P and of the oxygen isotope record of core V28-238 indicate the presence of a 23,000 year periodicity. Analysis of opal accumulation rate suggest a 100,000 year periodicity. These two periodicities are found in fluctuations in the earth's orbital parameters. The eccentricity of the orbit fluctuates with an average period of 98,000 years and the precession of the equinoxes changes with a 22,000 year period. Close

• 14. [Article] The use of foraminiferal uranium/calcium ratios as an indicator of changes in seawater uranium content

  We examine the utility of the uranium (U) content of planktonic foraminifera tests as an indicator of past changes in seawater U content. The U/Ca ratio in foraminifera from Atlantic and Caribbean cores ...

  Citation × Citation Citation Abstract Copy Title: The use of foraminiferal uranium/calcium ratios as an indicator of changes in seawater uranium content Author: Emerson, Steven, Peterson, Larry C., Russell, Ann D., Mix, Alan C. We examine the utility of the uranium (U) content of planktonic foraminifera tests as an indicator of past changes in seawater U content. The U/Ca ratio in foraminifera from Atlantic and Caribbean cores in constant in the Holocene and decreases by ~25% during the last glacial period. Magnesium/calcium (Mg/Ca) ratios of the same samples show similar trends. While the timing of the U/Ca changes appears to be associated with glacial-interglacial changes, the magnitude of the change is too large to be caused by variations in the extent of anoxic or suboxic sediments or by changes in riverine input. We assume that the same process produced changes in both U/Ca and Mg/Ca ratios because of a strong correlation between the two ratios. Partial dissolution of the calcite is ruled out, because we observe the same changes in well-preserved cores from basins with opposite dissolution histories. We also reject exchange between foraminiferal and pore water U because of the oxic depositional environment of both cores and because of the consistency in the U/Ca trends from cores in different parts of the ocean. We suggest that the observed foraminiferal U/Ca and Mg/Ca trends may be the result of a temperature effect on the incorporation of these metals. If this is true, it introduces the possibility of a new paleotemperature indicator but complicates the use of U/Ca ratios in planktonic foraminifera tests as an indicator of past seawater U changes. Title: The use of foraminiferal uranium/calcium ratios as an indicator of changes in seawater uranium content Author: Emerson, Steven, Peterson, Larry C., Russell, Ann D., Mix, Alan C. We examine the utility of the uranium (U) content of planktonic foraminifera tests as an indicator of past changes in seawater U content. The U/Ca ratio in foraminifera from Atlantic and Caribbean cores in constant in the Holocene and decreases by ~25% during the last glacial period. Magnesium/calcium (Mg/Ca) ratios of the same samples show similar trends. While the timing of the U/Ca changes appears to be associated with glacial-interglacial changes, the magnitude of the change is too large to be caused by variations in the extent of anoxic or suboxic sediments or by changes in riverine input. We assume that the same process produced changes in both U/Ca and Mg/Ca ratios because of a strong correlation between the two ratios. Partial dissolution of the calcite is ruled out, because we observe the same changes in well-preserved cores from basins with opposite dissolution histories. We also reject exchange between foraminiferal and pore water U because of the oxic depositional environment of both cores and because of the consistency in the U/Ca trends from cores in different parts of the ocean. We suggest that the observed foraminiferal U/Ca and Mg/Ca trends may be the result of a temperature effect on the incorporation of these metals. If this is true, it introduces the possibility of a new paleotemperature indicator but complicates the use of U/Ca ratios in planktonic foraminifera tests as an indicator of past seawater U changes. Close

• 15. [Article] Augmenting and interpreting ice core greenhouse gas records

  The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different ...

  Citation × Citation Citation Abstract Copy Title: Augmenting and interpreting ice core greenhouse gas records Author: Rosen, Julia L The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different gases and span the interval of time between the Last Glacial Maximum and the Industrial Revolution, but are united by their nontraditional use of greenhouse gases and their attempt to realize the potential for greenhouse gases to reveal important information about Earth’s climate. Ever since their discovery, the abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (D-O) events have proved challenging to explain. The dominant hypothesis involves periodic freshwater discharges into the North Atlantic, which may regulate the strength of the Meridional Overturning Circulation (MOC) and its role in transporting heat to high latitudes. These events were not restricted to the North Atlantic, and can also be recognized in paleoclimate archives around the world. However, numerous uncertainties surrounding the mechanism behind D-O events remain, including how they are communicated to low latitudes and whether other hypotheses can be definitively ruled out. To constrain the mechanism behind abrupt climate changes, we investigate the phasing of climate changes in high- and low-latitude regions at the Bølling Transition, the penultimate abrupt warming event of the last glacial period. We use methane and the ¹⁵N/¹⁴N ratio of N₂ from the North Greenland Eemian (NEEM) ice core, which serve as proxies for tropical climate and Greenland temperature, respectively. We find that these gases change synchronously in the ice core record, and use a firn air model together with a Monte Carlo approach to constrain the phase lag to within several decades. Our results indicate that the mechanism behind the Bølling Transition was capable of rapidly transmitting the climate signal across the planet in a matter of years, and must therefore involve components of the climate system that are suitably reactive. The glacial-interglacial change in atmospheric methane concentrations revealed in ice core records has spurred a decade of debate about its cause. The most likely explanations involve dramatic changes in methane emissions, which originate from both high- and low-latitude wetlands. One method of investigating the changing latitudinal distribution of methane sources is to quantify the difference in methane concentrations between Greenland and Antarctica, which changes in proportion to the fraction of methane produced at high northern latitudes. Previous attempts to determine the methane interpolar difference (IPD) abound, but many have been hampered by complications in synchronizing bipolar ice core records and analytical uncertainties. We present the first continuous estimate of the methane IPD across the termination using high-resolution methane data from the NEEM and West Antarctic Ice Sheet (WAIS) Divide ice cores. Our results reveal the dominant role of tropical sources in driving abrupt changes in atmospheric methane concentrations, and show that boreal methane sources were surprisingly insensitive to dramatic climate changes. We hypothesize that changes in Northern Hemisphere snow and ice cover exerted strong control over tropical methane emissions, while gradually increasing solar insolation and land area allowed boreal sources to grow during the termination. We also investigate the IPD across the major climate transitions of the termination, and during four centennial-scale methane variations, and find opposing trends in boreal and tropical source strengths during these transient events. We propose that temporary decoupling of the locus of interhemispheric mixing, the position of the Intertropical Convergence Zone, and tropical precipitation may explain these results. Atmospheric concentrations of nitrous oxide (N₂O) have risen by ~20% from preindustrial to modern times, but the cause of this increase is not fully understood. The change has been previously attributed to various agricultural activities which perturb microbial processes in soils, but exactly how remains an outstanding question with important implications for future mitigation of N₂O emissions. We present the first measurements of the isotopomers of tropospheric N₂O over the interval from 1450 to 1920 CE. Our results confirm that the preindustrial atmosphere was enriched in all isotopes relative to the modern atmosphere. Furthermore, we estimate that the net anthropogenic source of nitrous oxide must be depleted in all heavy isotopes and have a strong site preference, consistent with a strong role for agricultural emissions and characteristic of N₂O derived from nitrification. We also find a large oscillation in the site preference of the ¹⁵N in N₂O during the Little Ice Age between 1500 and 1700 CE. We hypothesize that this excursion may be due to changing climate conditions that led to an increase in the amount of N₂O produced by nitrification vs. denitrification. Title: Augmenting and interpreting ice core greenhouse gas records Author: Rosen, Julia L The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different gases and span the interval of time between the Last Glacial Maximum and the Industrial Revolution, but are united by their nontraditional use of greenhouse gases and their attempt to realize the potential for greenhouse gases to reveal important information about Earth’s climate. Ever since their discovery, the abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (D-O) events have proved challenging to explain. The dominant hypothesis involves periodic freshwater discharges into the North Atlantic, which may regulate the strength of the Meridional Overturning Circulation (MOC) and its role in transporting heat to high latitudes. These events were not restricted to the North Atlantic, and can also be recognized in paleoclimate archives around the world. However, numerous uncertainties surrounding the mechanism behind D-O events remain, including how they are communicated to low latitudes and whether other hypotheses can be definitively ruled out. To constrain the mechanism behind abrupt climate changes, we investigate the phasing of climate changes in high- and low-latitude regions at the Bølling Transition, the penultimate abrupt warming event of the last glacial period. We use methane and the ¹⁵N/¹⁴N ratio of N₂ from the North Greenland Eemian (NEEM) ice core, which serve as proxies for tropical climate and Greenland temperature, respectively. We find that these gases change synchronously in the ice core record, and use a firn air model together with a Monte Carlo approach to constrain the phase lag to within several decades. Our results indicate that the mechanism behind the Bølling Transition was capable of rapidly transmitting the climate signal across the planet in a matter of years, and must therefore involve components of the climate system that are suitably reactive. The glacial-interglacial change in atmospheric methane concentrations revealed in ice core records has spurred a decade of debate about its cause. The most likely explanations involve dramatic changes in methane emissions, which originate from both high- and low-latitude wetlands. One method of investigating the changing latitudinal distribution of methane sources is to quantify the difference in methane concentrations between Greenland and Antarctica, which changes in proportion to the fraction of methane produced at high northern latitudes. Previous attempts to determine the methane interpolar difference (IPD) abound, but many have been hampered by complications in synchronizing bipolar ice core records and analytical uncertainties. We present the first continuous estimate of the methane IPD across the termination using high-resolution methane data from the NEEM and West Antarctic Ice Sheet (WAIS) Divide ice cores. Our results reveal the dominant role of tropical sources in driving abrupt changes in atmospheric methane concentrations, and show that boreal methane sources were surprisingly insensitive to dramatic climate changes. We hypothesize that changes in Northern Hemisphere snow and ice cover exerted strong control over tropical methane emissions, while gradually increasing solar insolation and land area allowed boreal sources to grow during the termination. We also investigate the IPD across the major climate transitions of the termination, and during four centennial-scale methane variations, and find opposing trends in boreal and tropical source strengths during these transient events. We propose that temporary decoupling of the locus of interhemispheric mixing, the position of the Intertropical Convergence Zone, and tropical precipitation may explain these results. Atmospheric concentrations of nitrous oxide (N₂O) have risen by ~20% from preindustrial to modern times, but the cause of this increase is not fully understood. The change has been previously attributed to various agricultural activities which perturb microbial processes in soils, but exactly how remains an outstanding question with important implications for future mitigation of N₂O emissions. We present the first measurements of the isotopomers of tropospheric N₂O over the interval from 1450 to 1920 CE. Our results confirm that the preindustrial atmosphere was enriched in all isotopes relative to the modern atmosphere. Furthermore, we estimate that the net anthropogenic source of nitrous oxide must be depleted in all heavy isotopes and have a strong site preference, consistent with a strong role for agricultural emissions and characteristic of N₂O derived from nitrification. We also find a large oscillation in the site preference of the ¹⁵N in N₂O during the Little Ice Age between 1500 and 1700 CE. We hypothesize that this excursion may be due to changing climate conditions that led to an increase in the amount of N₂O produced by nitrification vs. denitrification. Close

• 16. [Article] Chronology reconstruction for the disturbed bottom section of the GISP2 and the GRIP ice cores: Implications for Termination II in Greenland

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/.

  Citation × Citation Citation Abstract Copy Title: Chronology reconstruction for the disturbed bottom section of the GISP2 and the GRIP ice cores: Implications for Termination II in Greenland Author: Brook, Edward J., Bender, Michael L., Landais, Amaelle, von Fischer, Joseph C., Suwa, Makoto This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. Title: Chronology reconstruction for the disturbed bottom section of the GISP2 and the GRIP ice cores: Implications for Termination II in Greenland Author: Brook, Edward J., Bender, Michael L., Landais, Amaelle, von Fischer, Joseph C., Suwa, Makoto This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. Close

• 17. [Article] A new mechanism for Dansgaard-Oeschger cycles

  This is the publisher’s final pdf. The published article is copyrighted by American Geophysical UnionAmerican Geophysical Union and can be found at: http://publications.agu.org/journals/.

  Citation × Citation Citation Abstract Copy Title: A new mechanism for Dansgaard-Oeschger cycles Author: Clark, P. U., Schrag, D. P., Petersen, S. V. This is the publisher’s final pdf. The published article is copyrighted by American Geophysical UnionAmerican Geophysical Union and can be found at: http://publications.agu.org/journals/. Title: A new mechanism for Dansgaard-Oeschger cycles Author: Clark, P. U., Schrag, D. P., Petersen, S. V. This is the publisher’s final pdf. The published article is copyrighted by American Geophysical UnionAmerican Geophysical Union and can be found at: http://publications.agu.org/journals/. Close

• 18. [Article] Silicic acid biogeochemistry in the Gulf of California: Insights from sedimentary Si isotopes

  This is the publisher’s final pdf. The published article is copyrighted by American Geophysical Union and can be found at: [link to journal].

  Citation × Citation Citation Abstract Copy Title: Silicic acid biogeochemistry in the Gulf of California: Insights from sedimentary Si isotopes Author: McClymont, Erin L., Ganeshram, Raja S., Thunell, Robert, Prahl, Fredrick, Pedersen, Thomas F., Pichevin, Laetitia, Reynolds, Ben C. This is the publisher’s final pdf. The published article is copyrighted by American Geophysical Union and can be found at: [link to journal]. Title: Silicic acid biogeochemistry in the Gulf of California: Insights from sedimentary Si isotopes Author: McClymont, Erin L., Ganeshram, Raja S., Thunell, Robert, Prahl, Fredrick, Pedersen, Thomas F., Pichevin, Laetitia, Reynolds, Ben C. This is the publisher’s final pdf. The published article is copyrighted by American Geophysical Union and can be found at: [link to journal]. Close

• 19. [Article] Glacial to holocene watermass and continental weathering reconstructions from the Southeast Pacific

  Sediments of the central Chile margin record changes in ocean circulation and continental erosion associated with large–scale climate change. Here Antarctic– influenced Southern Ocean currents flow equatorward, ...

  Citation × Citation Citation Abstract Copy Title: Glacial to holocene watermass and continental weathering reconstructions from the Southeast Pacific Author: Muratli, Jesse M. Sediments of the central Chile margin record changes in ocean circulation and continental erosion associated with large–scale climate change. Here Antarctic– influenced Southern Ocean currents flow equatorward, forming a link between the high– and low–latitude oceans. Part of this link, Antarctic Intermediate Water, is an important conduit that ventilates South Pacific subsurface and mid–depth waters. Differential weathering of the two parallel mountain ranges of Chile has been attributed to latitudinal shifts in the position of the southern westerly wind belt, with an equatorward shift increasing Coast Range rainfall and weathering rates. An increase in Coast Range weathering relative to Andean weathering has been proposed to reduce the delivery of iron to the marginal ocean, with implications for productivity in the Fe– limited Southern Ocean–derived waters. Sediments from three drill sites along the Chile margin (36°S–41°S, water depths ~500–1000 m) monitor changes in the extent and distribution of surface and subsurface ocean currents, as well as provenance of continental weathering products. Concentrations of the redox–sensitive metals Mn and Re in the sediments are controlled by bottom water oxygen. Decreasing concentrations of Mn and increased levels of Re relative to glacial–age concentrations suggest a deglacial poleward retreat of Antarctic Intermediate Water and subsequent expansion of low–oxygen water masses sourced from low latitudes. A suite of elements defines lithogenic contributions to the sediments, and a river sediment dataset provides a link to possible source regions on the continent. Rivers draining the Chilean Coast Range have similar Al concentrations to Andean rivers, but are poorer (relative to Al) in Ca, Mg, and Sr. Although Andean rocks have been hypothesized to be relatively iron–rich, levels of Fe/Al and Ti/Al are indistinguishable among river types. Marine sediments show reduced values of Mg/Al relative to glacial levels after deglaciation, suggesting a switch to a Coast Range source of material. This analysis implies that at latitudes south of 36°S ice sheet retreat after the glacial period caused an overall decrease in the rate of Andean weathering, which overwhelmed any signal of decreased Coast Range weathering driven by the poleward retreat of the westerly winds. In southern Chile (41°S) increased Holocene Ti/Al is interpreted as a switch after deglaciation to a Coast Range source rich in titanium. While weathering patterns, driven mainly by ice sheet changes, are not likely to change in a warming planet, recent observational trends in ocean circulation and intermediate water oxygen content suggest a future expansion of oxygen–minimum zones. Title: Glacial to holocene watermass and continental weathering reconstructions from the Southeast Pacific Author: Muratli, Jesse M. Sediments of the central Chile margin record changes in ocean circulation and continental erosion associated with large–scale climate change. Here Antarctic– influenced Southern Ocean currents flow equatorward, forming a link between the high– and low–latitude oceans. Part of this link, Antarctic Intermediate Water, is an important conduit that ventilates South Pacific subsurface and mid–depth waters. Differential weathering of the two parallel mountain ranges of Chile has been attributed to latitudinal shifts in the position of the southern westerly wind belt, with an equatorward shift increasing Coast Range rainfall and weathering rates. An increase in Coast Range weathering relative to Andean weathering has been proposed to reduce the delivery of iron to the marginal ocean, with implications for productivity in the Fe– limited Southern Ocean–derived waters. Sediments from three drill sites along the Chile margin (36°S–41°S, water depths ~500–1000 m) monitor changes in the extent and distribution of surface and subsurface ocean currents, as well as provenance of continental weathering products. Concentrations of the redox–sensitive metals Mn and Re in the sediments are controlled by bottom water oxygen. Decreasing concentrations of Mn and increased levels of Re relative to glacial–age concentrations suggest a deglacial poleward retreat of Antarctic Intermediate Water and subsequent expansion of low–oxygen water masses sourced from low latitudes. A suite of elements defines lithogenic contributions to the sediments, and a river sediment dataset provides a link to possible source regions on the continent. Rivers draining the Chilean Coast Range have similar Al concentrations to Andean rivers, but are poorer (relative to Al) in Ca, Mg, and Sr. Although Andean rocks have been hypothesized to be relatively iron–rich, levels of Fe/Al and Ti/Al are indistinguishable among river types. Marine sediments show reduced values of Mg/Al relative to glacial levels after deglaciation, suggesting a switch to a Coast Range source of material. This analysis implies that at latitudes south of 36°S ice sheet retreat after the glacial period caused an overall decrease in the rate of Andean weathering, which overwhelmed any signal of decreased Coast Range weathering driven by the poleward retreat of the westerly winds. In southern Chile (41°S) increased Holocene Ti/Al is interpreted as a switch after deglaciation to a Coast Range source rich in titanium. While weathering patterns, driven mainly by ice sheet changes, are not likely to change in a warming planet, recent observational trends in ocean circulation and intermediate water oxygen content suggest a future expansion of oxygen–minimum zones. Close

• 20. [Article] Cosmogenic ¹°Be chronology for the last deglaciation of the southern Scandinavian Ice Sheet

  The goal of this dissertation is to develop a chronology of the retreat of the southern margin of the Scandinavian Ice Sheet (SIS) during the late Pleistocene using surface exposure dating with cosmogenic ...

  Citation × Citation Citation Abstract Copy Title: Cosmogenic ¹°Be chronology for the last deglaciation of the southern Scandinavian Ice Sheet Author: Rinterknecht, Vincent R. The goal of this dissertation is to develop a chronology of the retreat of the southern margin of the Scandinavian Ice Sheet (SIS) during the late Pleistocene using surface exposure dating with cosmogenic 10Be. A sequence of seven prominent moraines in northeastern Europe (the Leszno Moraine, the Pomeranian Moraine, the Middle Lithuanian Moraine, the North Lithuanian Moraine, the P andivere Moraine, the Palivere Moraine, and the Salpausselka I Moraine) indicates a potential millennialscale record of climate variability. However, there are no direct dating constraints on the timing of this ice sheet retreat. Surface exposure dating using cosmogenic nuclide elements produced by secondary high-energy particles in the upper part of the lithosphere allows for direct dating of moraines deposited by the SIS. Cosmogenic 10Be concentrations were measured in quartz sampled from erratic boulders deposited on top of the moraines. The SIS margin withdrew from its maximum extent at 17,9 ± 2,4 10Be ka, which is correlative to the end of the Last Glacial Maximum period (23,0 to 19,0 ka). Following a recessional period, the ice readvanced to the Pomeranian Moraine. Deglaciation from this moraine is dated at 14,1 ± 1,8 10Be ka, and subsequent deglaciation is marked by the Middle Lithuanian Moraine (13,1 ± 1,7 "Be ka), the North Lithuanian Moraine (13,1 ± 1,7 10Be ka), the Pandivere Moraine (13,0 ± 1,1 10Be ka), the Palivere Moraine (10.0 ± 1,3 10Be ka), and the Salpausselka I Moraine (12,5 ± 1,5 10Be ka). This new chronology is compared to abrupt climate variability recorded in the North Atlantic region during the late Pleistocene. Paleo air temperatures recorded from the GISP2 ice core and paleo sea surface temperatures recorded from the North Atlantic region display warmings at the end of the Last Glacial Maximum period, during the Balling-Allerod interstadial, and at the end of the Younger Dryas stadial. These records also display abrupt coolings during the Oldest Dryas and the Younger Dryas stadials. Based on the 10Be chronology, the margin of the SIS responded to climate changes that occurred in the North Atlantic region. This new chronology contributes the first direct evidence of climate forcing on the southern margin of the SIS. Title: Cosmogenic ¹°Be chronology for the last deglaciation of the southern Scandinavian Ice Sheet Author: Rinterknecht, Vincent R. The goal of this dissertation is to develop a chronology of the retreat of the southern margin of the Scandinavian Ice Sheet (SIS) during the late Pleistocene using surface exposure dating with cosmogenic 10Be. A sequence of seven prominent moraines in northeastern Europe (the Leszno Moraine, the Pomeranian Moraine, the Middle Lithuanian Moraine, the North Lithuanian Moraine, the P andivere Moraine, the Palivere Moraine, and the Salpausselka I Moraine) indicates a potential millennialscale record of climate variability. However, there are no direct dating constraints on the timing of this ice sheet retreat. Surface exposure dating using cosmogenic nuclide elements produced by secondary high-energy particles in the upper part of the lithosphere allows for direct dating of moraines deposited by the SIS. Cosmogenic 10Be concentrations were measured in quartz sampled from erratic boulders deposited on top of the moraines. The SIS margin withdrew from its maximum extent at 17,9 ± 2,4 10Be ka, which is correlative to the end of the Last Glacial Maximum period (23,0 to 19,0 ka). Following a recessional period, the ice readvanced to the Pomeranian Moraine. Deglaciation from this moraine is dated at 14,1 ± 1,8 10Be ka, and subsequent deglaciation is marked by the Middle Lithuanian Moraine (13,1 ± 1,7 "Be ka), the North Lithuanian Moraine (13,1 ± 1,7 10Be ka), the Pandivere Moraine (13,0 ± 1,1 10Be ka), the Palivere Moraine (10.0 ± 1,3 10Be ka), and the Salpausselka I Moraine (12,5 ± 1,5 10Be ka). This new chronology is compared to abrupt climate variability recorded in the North Atlantic region during the late Pleistocene. Paleo air temperatures recorded from the GISP2 ice core and paleo sea surface temperatures recorded from the North Atlantic region display warmings at the end of the Last Glacial Maximum period, during the Balling-Allerod interstadial, and at the end of the Younger Dryas stadial. These records also display abrupt coolings during the Oldest Dryas and the Younger Dryas stadials. Based on the 10Be chronology, the margin of the SIS responded to climate changes that occurred in the North Atlantic region. This new chronology contributes the first direct evidence of climate forcing on the southern margin of the SIS. Close

• 21. [Article] Paleo-oceanography of the Gulf of California based on silicoflagellates from marine varved sediments

  Plankton and surface sediment samples from the Gulf of California were analyzed to determine the present geographic distribution of silicoflagellate species in this area. Variations in the composition ...

  Citation × Citation Citation Abstract Copy Title: Paleo-oceanography of the Gulf of California based on silicoflagellates from marine varved sediments Author: Murray, David W. Plankton and surface sediment samples from the Gulf of California were analyzed to determine the present geographic distribution of silicoflagellate species in this area. Variations in the composition of the silicoflagellate assemblage are related to water mass distributions. Seven species and three forms were identified in these samples. Octactis pulchra is associated with high levels of primary productivity in the surface waters and is found in greatest abundance in the central Gulf of California. Dictyocha messanensis dominates the silicoflagellate assemblage in stations outside the Gulf of California and increases in relative abundance with decreasing amounts of 0. pulchra. D. calida and D. spec. 1 forms are associated with equatorial waters and have the highest relative abundance near the mouth of the Gulf. D. epiodon and Distephanus speculum are associated with cold California Current Water and Dictyocha epiodon is present in minor abundance in Gulf samples. D. spec. 2 has a patchy distribution with low relative abundance in these samples. Downcore sediment samples were analyzed from six locations in the southern Gulf of California. The results suggest that major variations in the relative composition of the silicoflagellate assemblage have not occurred over the past 1000 years. Sediment material obtained from the basin slopes in the central Gulf of California exhibit alternating light and dark laminations. A laminae couplet equals one year of deposition. The composition of the silicoflagellate assemblage was determined in one hundred twenty individual laminae samples from the top section of a box core from the central Gulf. There is no indication of a characteristic assemblage composition associated with either light or dark laminations in these samples. A high relative abundance of 0. pulchra is present in the well laminated sections of the core. D. spec. 1, D. epiodon, D. calida, and D. spec. 2 are periodically in great abundance spanning more than one laminae sample. Variations in the relative abundance of silicoflagellate species in the central Gulf of California during the last 38,000 years were determined from DSDP Leg 64 Site 480 samples. The results indicate that 0. pulchra was in lower relative abundance and Distephanus speculum, Dictyocha epiodon, and D. spec. 1 forms were in greater abundance during the glacial period compared to the present. This suggests that there was a decrease in primary production, an increase in Pacific water influence, and a decrease in surface water temperatures in the central Gulf of California during the last major glacial interval compared to the present conditions. Title: Paleo-oceanography of the Gulf of California based on silicoflagellates from marine varved sediments Author: Murray, David W. Plankton and surface sediment samples from the Gulf of California were analyzed to determine the present geographic distribution of silicoflagellate species in this area. Variations in the composition of the silicoflagellate assemblage are related to water mass distributions. Seven species and three forms were identified in these samples. Octactis pulchra is associated with high levels of primary productivity in the surface waters and is found in greatest abundance in the central Gulf of California. Dictyocha messanensis dominates the silicoflagellate assemblage in stations outside the Gulf of California and increases in relative abundance with decreasing amounts of 0. pulchra. D. calida and D. spec. 1 forms are associated with equatorial waters and have the highest relative abundance near the mouth of the Gulf. D. epiodon and Distephanus speculum are associated with cold California Current Water and Dictyocha epiodon is present in minor abundance in Gulf samples. D. spec. 2 has a patchy distribution with low relative abundance in these samples. Downcore sediment samples were analyzed from six locations in the southern Gulf of California. The results suggest that major variations in the relative composition of the silicoflagellate assemblage have not occurred over the past 1000 years. Sediment material obtained from the basin slopes in the central Gulf of California exhibit alternating light and dark laminations. A laminae couplet equals one year of deposition. The composition of the silicoflagellate assemblage was determined in one hundred twenty individual laminae samples from the top section of a box core from the central Gulf. There is no indication of a characteristic assemblage composition associated with either light or dark laminations in these samples. A high relative abundance of 0. pulchra is present in the well laminated sections of the core. D. spec. 1, D. epiodon, D. calida, and D. spec. 2 are periodically in great abundance spanning more than one laminae sample. Variations in the relative abundance of silicoflagellate species in the central Gulf of California during the last 38,000 years were determined from DSDP Leg 64 Site 480 samples. The results indicate that 0. pulchra was in lower relative abundance and Distephanus speculum, Dictyocha epiodon, and D. spec. 1 forms were in greater abundance during the glacial period compared to the present. This suggests that there was a decrease in primary production, an increase in Pacific water influence, and a decrease in surface water temperatures in the central Gulf of California during the last major glacial interval compared to the present conditions. Close

• 22. [Article] Past climate variability in southwestern Oregon and relationships with regional and hemispheric climate

  This dissertation presents the results of three studies that assessed climate variability on short and long timescales in western United States. The growth of carbonate formations in caves (speleothems) ...

  Citation × Citation Citation Abstract Copy Title: Past climate variability in southwestern Oregon and relationships with regional and hemispheric climate Author: Ersek, Vasile This dissertation presents the results of three studies that assessed climate variability on short and long timescales in western United States. The growth of carbonate formations in caves (speleothems) is used to infer the timing and amplitude of past climate variability. We first assess the controls on speleothem growth for the past 380 000 years by combining high-density U-Th dating with a regional climate model and an energy balance model. The majority of speleothem growth occurred overwhelmingly during interglacial periods and glacial periods were characterized by little or no growth. We assess the mechanisms responsible for growth cessation during the peak of the last glaciation (LGM), 21 000 years ago, with a regional climate model and determine that a combination of drier LGM conditions with a change in the seasonal cycle of the surface water balance provides a feedback mechanism that limited recharge to the deeper soil and reduced or eliminated drip water in the cave. The energy balance model supports this mechanism by indicating that cave temperatures did not drop below the freezing point of water at any time during the last glaciation. We then evaluate the climatic significance of stable isotopes of oxygen in rainwater collected in southwestern Oregon in order to accurately interpret the isotopic record of speleothems. We establish that temperature plays an important role in controlling the distribution of oxygen isotopes in rainwater and therefore speleothems in southwestern Oregon can preserve a record of temperature changes through time. Finally, we present a high-resolution paleoclimate record using speleothems from a cave in Oregon that grew during the last 9000 years and during the middle of the last interglaciation. We find the winter temperatures were sensitive to winter solar insolation and varied in a quasi-cyclical pattern on millennial timescales. This pattern was characteristic of both regional and hemispheric variability as indicated by similarities of our record with other regional and hemispheric climate reconstructions. It appears that higher climate variability in the past was associated with warming trends, with the implication that global warming may make the climate more unstable in the future. Climate variability during the last interglacial period was characterized by different scales of millennial and centennial climate variability compared with the Holocene. Title: Past climate variability in southwestern Oregon and relationships with regional and hemispheric climate Author: Ersek, Vasile This dissertation presents the results of three studies that assessed climate variability on short and long timescales in western United States. The growth of carbonate formations in caves (speleothems) is used to infer the timing and amplitude of past climate variability. We first assess the controls on speleothem growth for the past 380 000 years by combining high-density U-Th dating with a regional climate model and an energy balance model. The majority of speleothem growth occurred overwhelmingly during interglacial periods and glacial periods were characterized by little or no growth. We assess the mechanisms responsible for growth cessation during the peak of the last glaciation (LGM), 21 000 years ago, with a regional climate model and determine that a combination of drier LGM conditions with a change in the seasonal cycle of the surface water balance provides a feedback mechanism that limited recharge to the deeper soil and reduced or eliminated drip water in the cave. The energy balance model supports this mechanism by indicating that cave temperatures did not drop below the freezing point of water at any time during the last glaciation. We then evaluate the climatic significance of stable isotopes of oxygen in rainwater collected in southwestern Oregon in order to accurately interpret the isotopic record of speleothems. We establish that temperature plays an important role in controlling the distribution of oxygen isotopes in rainwater and therefore speleothems in southwestern Oregon can preserve a record of temperature changes through time. Finally, we present a high-resolution paleoclimate record using speleothems from a cave in Oregon that grew during the last 9000 years and during the middle of the last interglaciation. We find the winter temperatures were sensitive to winter solar insolation and varied in a quasi-cyclical pattern on millennial timescales. This pattern was characteristic of both regional and hemispheric variability as indicated by similarities of our record with other regional and hemispheric climate reconstructions. It appears that higher climate variability in the past was associated with warming trends, with the implication that global warming may make the climate more unstable in the future. Climate variability during the last interglacial period was characterized by different scales of millennial and centennial climate variability compared with the Holocene. Close

• 23. [Article] Onset of deglacial warming in West Antarctica driven by local orbital forcing

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Macmillan ...

  Citation × Citation Citation Abstract Copy Title: Onset of deglacial warming in West Antarctica driven by local orbital forcing Author: Mortensen, Nicolai, Edwards, R. Lawrence, Popp, Trevor J., Brook, Edward J., Neff, Peter, Edwards, Ross, Sowers, Todd, Cole-Dai, Jihong, Markle, Bradley R., Johnson, Jay, Hargreaves, Geoffrey, Schauer, Andrew J., Cuffey, Kurt M., Fegyveresi, John M., White, James W. C., Alley, Richard B., Clow, Gary D., McGwire, Kenneth C., Ding, Qinghua, Mitchell, Logan E., Fitzpatrick, Joan J., Schoenemann, Spruce W., Steig, Eric J., Fudge, T. J., Maselli, Olivia J., Mason, William, Ferris, David, Orsi, Anais J., Edwards, Jon S., Taylor, Kendrick C., McConnell, Joseph R., Conway, Howard, Lee, James E., Cheng, Hai To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Macmillan Publishers Limited and can be found at: http://www.macmillan.com/. Title: Onset of deglacial warming in West Antarctica driven by local orbital forcing Author: Mortensen, Nicolai, Edwards, R. Lawrence, Popp, Trevor J., Brook, Edward J., Neff, Peter, Edwards, Ross, Sowers, Todd, Cole-Dai, Jihong, Markle, Bradley R., Johnson, Jay, Hargreaves, Geoffrey, Schauer, Andrew J., Cuffey, Kurt M., Fegyveresi, John M., White, James W. C., Alley, Richard B., Clow, Gary D., McGwire, Kenneth C., Ding, Qinghua, Mitchell, Logan E., Fitzpatrick, Joan J., Schoenemann, Spruce W., Steig, Eric J., Fudge, T. J., Maselli, Olivia J., Mason, William, Ferris, David, Orsi, Anais J., Edwards, Jon S., Taylor, Kendrick C., McConnell, Joseph R., Conway, Howard, Lee, James E., Cheng, Hai To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Macmillan Publishers Limited and can be found at: http://www.macmillan.com/. Close

• 24. [Article] Relative timing and variability of atmospheric methane and GISP2 oxygen isotopes between 68 and 86 ka

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gb/index.shtml.

  Citation × Citation Citation Abstract Copy Title: Relative timing and variability of atmospheric methane and GISP2 oxygen isotopes between 68 and 86 ka Author: Brook, Edward J., Severinghaus, Jeffrey P., Grachev, Alexi M., Pisias, Nicklas G. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gb/index.shtml. Title: Relative timing and variability of atmospheric methane and GISP2 oxygen isotopes between 68 and 86 ka Author: Brook, Edward J., Severinghaus, Jeffrey P., Grachev, Alexi M., Pisias, Nicklas G. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gb/index.shtml. Close

• 25. [Article] Precise interpolar phasing of abrupt climate change during the last ice age

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Nature ...

  Citation × Citation Citation Abstract Copy Title: Precise interpolar phasing of abrupt climate change during the last ice age Author: Rhodes, Rachael H., Rosen, Julia L., Kalk, Michael L., Buizert, Christo, Edwards, Jon S., Adrian, Betty, Bauska, Thomas K., Marcott, Shaun A., et al., Mitchell, Logan E., Lee, James E., Brook, Edward J., Ahn, Jinho To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Nature Publishing Group and can be found at: http://www.nature.com/nature/index.html. Supporting Information can be found at: http://www.nature.com/nature/journal/v520/n7549/full/nature14401.html#/supplementary-information Title: Precise interpolar phasing of abrupt climate change during the last ice age Author: Rhodes, Rachael H., Rosen, Julia L., Kalk, Michael L., Buizert, Christo, Edwards, Jon S., Adrian, Betty, Bauska, Thomas K., Marcott, Shaun A., et al., Mitchell, Logan E., Lee, James E., Brook, Edward J., Ahn, Jinho To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Nature Publishing Group and can be found at: http://www.nature.com/nature/index.html. Supporting Information can be found at: http://www.nature.com/nature/journal/v520/n7549/full/nature14401.html#/supplementary-information Close

• 26. [Article] The WAIS Divide deep ice core WD2014 chronology - Part 2: Annual-layer counting (0-31 ka BP)

  This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can ...

  Citation × Citation Citation Abstract Copy Title: The WAIS Divide deep ice core WD2014 chronology - Part 2: Annual-layer counting (0-31 ka BP) Author: Layman, Lawrence, Brook, Edward J., Caffee, Marc W., Edwards, Ross, Ferris, David, Buizert, Christo, Cole-Dai, Jihong, Fudge, Tyler J., Woodruff, Thomas E., Taylor, Ken C., McConnell, Joseph R., Nishiizumi, Kunihiko, McGwire, Kenneth, Sigl, Michael, Muscheler, Raimund, Koffman, Bess, Iverson, Nels, Welten, Kees C., Sowers, Todd A, Rhodes, Rachael H., Maselli, Olivia J., Geng, Lei, Pasteris, Daniel R., Dunbar, Nelia W., Bisiaux, Marion, Winstrup, Mai, Adolphi, Florian This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.climate-of-the-past.net/ Title: The WAIS Divide deep ice core WD2014 chronology - Part 2: Annual-layer counting (0-31 ka BP) Author: Layman, Lawrence, Brook, Edward J., Caffee, Marc W., Edwards, Ross, Ferris, David, Buizert, Christo, Cole-Dai, Jihong, Fudge, Tyler J., Woodruff, Thomas E., Taylor, Ken C., McConnell, Joseph R., Nishiizumi, Kunihiko, McGwire, Kenneth, Sigl, Michael, Muscheler, Raimund, Koffman, Bess, Iverson, Nels, Welten, Kees C., Sowers, Todd A, Rhodes, Rachael H., Maselli, Olivia J., Geng, Lei, Pasteris, Daniel R., Dunbar, Nelia W., Bisiaux, Marion, Winstrup, Mai, Adolphi, Florian This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.climate-of-the-past.net/ Close

• 27. [Article] Geology, geomorphology, and dynamics of mass movement in parts of the Middle Santiam River drainage basin, western Cascades, Oregon

  Landforms sculpted by mass movements comprise much of the landscape in the Middle Santiam study area. Bedrock in the area is mostly basalt and andesite flows and varied volcaniclastic rocks of the Little ...

  Citation × Citation Citation Abstract Copy Title: Geology, geomorphology, and dynamics of mass movement in parts of the Middle Santiam River drainage basin, western Cascades, Oregon Author: Hicks, Bryan A. Landforms sculpted by mass movements comprise much of the landscape in the Middle Santiam study area. Bedrock in the area is mostly basalt and andesite flows and varied volcaniclastic rocks of the Little Butte Volcanic Series of Oligocene and early Miocene age, unconforniably overlain by andesite flows and tuffs of the Sardine Formation of middle and late Miocene age. Some mass movements in the study area may have originally occurred during glacial or interglacial periods of the late Pleistocene, although this is largely speculative. Active slump-earthflows, debris avalanches, and debris torrents impact streams, timber resources and man-made structures. Earthflows are associated with intercalated lava flows and volcaniclastics, especially stratified volcaniclastics which have low strength, high plasticity, and contain montmorillonite, an expandable clay mineral. Debris avalanches are associated with non-cohesive soils on steep slopes. Slump-earthflows show distinctive morphological and vegetative characteristics which reflect recency and rates of movement. Areas with different levels of activity can be mapped and the data used for certain land-planning applications. Surface movement rates can be measured on active earthflows by conventional surveying and the use of stake arrays. Results indicate that rapid surface movement exceeding 20 ft/yr is occurring on at least two earthflows, and that intraannual and annual periods of accelerated movement coincide with periods of greater water input from precipitation and snowmelt Movement of the Jude Creek earthflow also appears to be related to erosion of the toe by Jude Creek Movement on the Middle Santiam earthflow has greatly accelerated in the last three years (since 1978), compared with average rates for the previous 13 years Road construction in 1965 preceded the most recent pulse of movement at this site Inventory of debris avalanches in the study area indicate a link between road construction, storm history and debris avalanche occurrence Rates of soil transfer for road-related events is much greater than those for either forested or clearcut events. Title: Geology, geomorphology, and dynamics of mass movement in parts of the Middle Santiam River drainage basin, western Cascades, Oregon Author: Hicks, Bryan A. Landforms sculpted by mass movements comprise much of the landscape in the Middle Santiam study area. Bedrock in the area is mostly basalt and andesite flows and varied volcaniclastic rocks of the Little Butte Volcanic Series of Oligocene and early Miocene age, unconforniably overlain by andesite flows and tuffs of the Sardine Formation of middle and late Miocene age. Some mass movements in the study area may have originally occurred during glacial or interglacial periods of the late Pleistocene, although this is largely speculative. Active slump-earthflows, debris avalanches, and debris torrents impact streams, timber resources and man-made structures. Earthflows are associated with intercalated lava flows and volcaniclastics, especially stratified volcaniclastics which have low strength, high plasticity, and contain montmorillonite, an expandable clay mineral. Debris avalanches are associated with non-cohesive soils on steep slopes. Slump-earthflows show distinctive morphological and vegetative characteristics which reflect recency and rates of movement. Areas with different levels of activity can be mapped and the data used for certain land-planning applications. Surface movement rates can be measured on active earthflows by conventional surveying and the use of stake arrays. Results indicate that rapid surface movement exceeding 20 ft/yr is occurring on at least two earthflows, and that intraannual and annual periods of accelerated movement coincide with periods of greater water input from precipitation and snowmelt Movement of the Jude Creek earthflow also appears to be related to erosion of the toe by Jude Creek Movement on the Middle Santiam earthflow has greatly accelerated in the last three years (since 1978), compared with average rates for the previous 13 years Road construction in 1965 preceded the most recent pulse of movement at this site Inventory of debris avalanches in the study area indicate a link between road construction, storm history and debris avalanche occurrence Rates of soil transfer for road-related events is much greater than those for either forested or clearcut events. Close

• 28. [Article] Abrupt deglacial climate changes in the North Pacific and implications for climate tipping points

  Paleoclimate archives have revealed abrupt climate events that are superimposed on more gradual climate changes throughout the last glacial and deglacial periods. The underlying causes of such rapid climate ...

  Citation × Citation Citation Abstract Copy Title: Abrupt deglacial climate changes in the North Pacific and implications for climate tipping points Author: Praetorius, Summer Kate Paleoclimate archives have revealed abrupt climate events that are superimposed on more gradual climate changes throughout the last glacial and deglacial periods. The underlying causes of such rapid climate changes are still poorly understood, but the strong expression of these events in northern hemisphere records likely points to climatic mechanisms of a northern origin. A leading hypothesis for the trigger of these climate fluctuations has been changes in the strength of the Atlantic meridional overturning circulation (AMOC). However, the very rapid nature of some of the observed climate transitions (3-50 years) suggests a potential role for abrupt shifts in atmospheric circulation or nonlinear feedbacks within the climate system. Understanding the relative timing and magnitude of these events in different regions of the globe will help to identify the sources and possible amplifying mechanisms that have led to abrupt climate changes in the past, which will provide insight and constraints on the potential for abrupt climate changes in the future. This dissertation seeks to characterize climate changes occurring in the Northeast Pacific during the last deglaciation, a time period that encompasses the dynamic transition between the last ice age and the modern day interglacial period. So far, high-resolution records with precise chronologies from the North Pacific have been sparse, and paleoclimate models and proxy reconstructions disagree about the deglacial climate changes that are both predicted and observed to have occurred in this region. Marine sediment records from the Gulf of Alaska (GOA) have exceptionally high resolution (~1 cm/yr), making it possible to reconstruct climate changes in unprecedented detail for the North Pacific region. We establish new multi-decadal scale records of surface ocean variability using planktonic oxygen isotopes and sea-surface temperature (SST) estimates based on the alkenone U₃₇[superscript K'] unsaturation index, as well as regional records of ice-rafting and deglacial volcanic activity sourced from the Mt. Edgecumbe volcanic field (MEVF). The age models for these records are constrained by high-precision radiocarbon dating, tephra correlation, and "tuning" to the decadal-scale North Greenland Ice Core Project (NGRIP) oxygen isotope record. We combine new and previously published data from a depth transect of marine sites in the GOA and Northeast Pacific to place surface ocean changes in context of oceanic variability throughout the water column. These reconstructions are then used to evaluate three fundamental questions: 1) what are the timing and patterns of deglacial climate changes in the North Pacific relative to other regions, 2) what are the potential forcing mechanisms for deglacial climate variability in this region, and 3) how does the subsurface ocean respond to and influence abrupt climate change. In chapter two, we compare the timing and patterns of climate changes occurring between the North Pacific and North Atlantic regions. A major debate in the paleoclimate literature has been whether these regions operate in a synchronized or seesaw like mode. We compare the high resolution GOA and NGRIP oxygen isotope records as proxies for local temperature, and find that both synchronous and asynchronous climate patterns occur between regions throughout the past 18,000 years. The most abrupt climate transitions are preceded/accompanied by synchronous behavior, whereas times of relative climate stability exhibit asynchronous or anticorrelated (seesaw) patterns. This implies that coupling of North Pacific and North Atlantic heat transport could act as an amplifying mechanism in abrupt northern hemisphere climate change, whereas opposing oceanic regimes could act to balance northern hemisphere heat transport, and thus promote climate stability. In chapter three, we examine the timing between regional deglaciation and volcanism to evaluate potential feedbacks between climate and volcanic activity. Although volcanic eruptions have been observed to contribute to abrupt climate fluctuations with global effects in historical times, the role of volcanic forcing in climate variability of the more distant past (prior to the Holocene) has been neglected due to the very short-time scales in which volcanic events occur, and the difficulty of obtaining records with high enough resolution to capture these events and their associated climate effects. We evaluate the source and timing of a sequence of 23 tephra layers preserved in high-accumulation rate sediment cores proximal to the MEVF, and examine the regional climate response to this volcanic activity through comparison with reconstructions of sea surface temperatures, oxygen isotopes, and the δ¹⁸O of seawater. We find that the onset of enhanced volcanic activity coincides with abrupt warming at the onset of the Bølling Allerød, regional retreat of glaciers, and a period of rapid vertical land motion predicted from a model of regional isostatic rebound. These finding support the hypothesis that deglaciation may promote volcanism by removing crustal loading. The records of sea surface variability show large fluctuations during the episode of intense volcanic activity, suggesting that deglacial volcanic activity may not only respond to climate, but may also contribute to climate variance during the deglacial interval. In Chapter four, we examine the oceanographic changes that lead to two episodes of hypoxia in the GOA that lasted for millennia during the deglaciation. Similar hypoxic events have been documented across the North Pacific, indicating a widespread expansion of the oxygen minimum zone (OMZ) during the Bølling Allerød and early Holocene warm periods. These episodes have been linked to enhanced export productivity in many sites, however, the driving mechanisms for enhanced productivity and ocean deoxygenation remain elusive. Our alkenone temperature reconstructions reveal two abrupt warmings of 4-5°C that precisely coincide with the onset of increased export productivity and a sudden shift to hypoxic conditions, suggesting a strong link between ocean warming, marine productivity, and deoxygenation. Oxygen isotopes throughout the water column indicate that a transient subsurface warming of ~2°C might have accompanied the first hypoxic event during the BA. We propose that abrupt ocean warming lead to an expansion of the North Pacific OMZ through a reduction in oxygen solubility, enhanced thermal stratification, and a stimulation of marine productivity through the stabilization of the euphotic zone (related to stratification), combined with enhanced nutrient input from remobilization of iron in hypoxic shelf sediments. These studies indicate that large surface and subsurface ocean changes occurred in the North Pacific during the last deglaciation, with the potential for important feedbacks on global climate. Title: Abrupt deglacial climate changes in the North Pacific and implications for climate tipping points Author: Praetorius, Summer Kate Paleoclimate archives have revealed abrupt climate events that are superimposed on more gradual climate changes throughout the last glacial and deglacial periods. The underlying causes of such rapid climate changes are still poorly understood, but the strong expression of these events in northern hemisphere records likely points to climatic mechanisms of a northern origin. A leading hypothesis for the trigger of these climate fluctuations has been changes in the strength of the Atlantic meridional overturning circulation (AMOC). However, the very rapid nature of some of the observed climate transitions (3-50 years) suggests a potential role for abrupt shifts in atmospheric circulation or nonlinear feedbacks within the climate system. Understanding the relative timing and magnitude of these events in different regions of the globe will help to identify the sources and possible amplifying mechanisms that have led to abrupt climate changes in the past, which will provide insight and constraints on the potential for abrupt climate changes in the future. This dissertation seeks to characterize climate changes occurring in the Northeast Pacific during the last deglaciation, a time period that encompasses the dynamic transition between the last ice age and the modern day interglacial period. So far, high-resolution records with precise chronologies from the North Pacific have been sparse, and paleoclimate models and proxy reconstructions disagree about the deglacial climate changes that are both predicted and observed to have occurred in this region. Marine sediment records from the Gulf of Alaska (GOA) have exceptionally high resolution (~1 cm/yr), making it possible to reconstruct climate changes in unprecedented detail for the North Pacific region. We establish new multi-decadal scale records of surface ocean variability using planktonic oxygen isotopes and sea-surface temperature (SST) estimates based on the alkenone U₃₇[superscript K'] unsaturation index, as well as regional records of ice-rafting and deglacial volcanic activity sourced from the Mt. Edgecumbe volcanic field (MEVF). The age models for these records are constrained by high-precision radiocarbon dating, tephra correlation, and "tuning" to the decadal-scale North Greenland Ice Core Project (NGRIP) oxygen isotope record. We combine new and previously published data from a depth transect of marine sites in the GOA and Northeast Pacific to place surface ocean changes in context of oceanic variability throughout the water column. These reconstructions are then used to evaluate three fundamental questions: 1) what are the timing and patterns of deglacial climate changes in the North Pacific relative to other regions, 2) what are the potential forcing mechanisms for deglacial climate variability in this region, and 3) how does the subsurface ocean respond to and influence abrupt climate change. In chapter two, we compare the timing and patterns of climate changes occurring between the North Pacific and North Atlantic regions. A major debate in the paleoclimate literature has been whether these regions operate in a synchronized or seesaw like mode. We compare the high resolution GOA and NGRIP oxygen isotope records as proxies for local temperature, and find that both synchronous and asynchronous climate patterns occur between regions throughout the past 18,000 years. The most abrupt climate transitions are preceded/accompanied by synchronous behavior, whereas times of relative climate stability exhibit asynchronous or anticorrelated (seesaw) patterns. This implies that coupling of North Pacific and North Atlantic heat transport could act as an amplifying mechanism in abrupt northern hemisphere climate change, whereas opposing oceanic regimes could act to balance northern hemisphere heat transport, and thus promote climate stability. In chapter three, we examine the timing between regional deglaciation and volcanism to evaluate potential feedbacks between climate and volcanic activity. Although volcanic eruptions have been observed to contribute to abrupt climate fluctuations with global effects in historical times, the role of volcanic forcing in climate variability of the more distant past (prior to the Holocene) has been neglected due to the very short-time scales in which volcanic events occur, and the difficulty of obtaining records with high enough resolution to capture these events and their associated climate effects. We evaluate the source and timing of a sequence of 23 tephra layers preserved in high-accumulation rate sediment cores proximal to the MEVF, and examine the regional climate response to this volcanic activity through comparison with reconstructions of sea surface temperatures, oxygen isotopes, and the δ¹⁸O of seawater. We find that the onset of enhanced volcanic activity coincides with abrupt warming at the onset of the Bølling Allerød, regional retreat of glaciers, and a period of rapid vertical land motion predicted from a model of regional isostatic rebound. These finding support the hypothesis that deglaciation may promote volcanism by removing crustal loading. The records of sea surface variability show large fluctuations during the episode of intense volcanic activity, suggesting that deglacial volcanic activity may not only respond to climate, but may also contribute to climate variance during the deglacial interval. In Chapter four, we examine the oceanographic changes that lead to two episodes of hypoxia in the GOA that lasted for millennia during the deglaciation. Similar hypoxic events have been documented across the North Pacific, indicating a widespread expansion of the oxygen minimum zone (OMZ) during the Bølling Allerød and early Holocene warm periods. These episodes have been linked to enhanced export productivity in many sites, however, the driving mechanisms for enhanced productivity and ocean deoxygenation remain elusive. Our alkenone temperature reconstructions reveal two abrupt warmings of 4-5°C that precisely coincide with the onset of increased export productivity and a sudden shift to hypoxic conditions, suggesting a strong link between ocean warming, marine productivity, and deoxygenation. Oxygen isotopes throughout the water column indicate that a transient subsurface warming of ~2°C might have accompanied the first hypoxic event during the BA. We propose that abrupt ocean warming lead to an expansion of the North Pacific OMZ through a reduction in oxygen solubility, enhanced thermal stratification, and a stimulation of marine productivity through the stabilization of the euphotic zone (related to stratification), combined with enhanced nutrient input from remobilization of iron in hypoxic shelf sediments. These studies indicate that large surface and subsurface ocean changes occurred in the North Pacific during the last deglaciation, with the potential for important feedbacks on global climate. Close

• 29. [Article] Basal temperature evolution of North American ice sheets and implications for the 100-kyr cycle

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/.

  Citation × Citation Citation Abstract Copy Title: Basal temperature evolution of North American ice sheets and implications for the 100-kyr cycle Author: Marshall, Shawn J., Clark, Peter U. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Title: Basal temperature evolution of North American ice sheets and implications for the 100-kyr cycle Author: Marshall, Shawn J., Clark, Peter U. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gl/. Close

• 30. [Article] Cenozoic biogenic silica sedimentation in the Antarctic Ocean, based on two deep sea drilling project sites

  The Antarctic Ocean during the Cenozoic experienced four periods of increased surface productivity: the Middle Eocene; the beginning of the Miocene; the Middle Miocene; and near the Miocene-Pliocene boundary. ...

  Citation × Citation Citation Abstract Copy Title: Cenozoic biogenic silica sedimentation in the Antarctic Ocean, based on two deep sea drilling project sites Author: Brewster, Nancy Ann The Antarctic Ocean during the Cenozoic experienced four periods of increased surface productivity: the Middle Eocene; the beginning of the Miocene; the Middle Miocene; and near the Miocene-Pliocene boundary. The fourth increase in productivity began five million years ago and has since progressively increased to the present level of intense surface productivity. The major control of Antarctic surface productivity is climate. Opal production in the Neogene increased during glacial times, due to the intensification of upwelling south of the Polar Front, caused from accelerated atmospheric circulation and an increased volume production of Antarctic Bottom Water. Cenozoic variations in surface productivity are also related to the tectonic changes in the Antarctic Ocean basin, which altered the patterns of surface and thermohaline circulation. Antarctic Surface Waters became more conducive to biological productivity with the progressive latitudinal and thermal isolation of Antarctica, The efficiency of surface productivity has progressed to such an extent that much of the global silica supply has been transferred to the Antarctic at the expense of other productive oceanic regions such as the Central Equatorial Pacific. In the Neogene, the preservation or dissolution of calcium carbonate is influenced by the rate of upwelling south of the Polar Front. During glacial times, the upwelling of COB_rich Circumpolar Deep Water accelerates and effectively raises the calcite compensation depth. Title: Cenozoic biogenic silica sedimentation in the Antarctic Ocean, based on two deep sea drilling project sites Author: Brewster, Nancy Ann The Antarctic Ocean during the Cenozoic experienced four periods of increased surface productivity: the Middle Eocene; the beginning of the Miocene; the Middle Miocene; and near the Miocene-Pliocene boundary. The fourth increase in productivity began five million years ago and has since progressively increased to the present level of intense surface productivity. The major control of Antarctic surface productivity is climate. Opal production in the Neogene increased during glacial times, due to the intensification of upwelling south of the Polar Front, caused from accelerated atmospheric circulation and an increased volume production of Antarctic Bottom Water. Cenozoic variations in surface productivity are also related to the tectonic changes in the Antarctic Ocean basin, which altered the patterns of surface and thermohaline circulation. Antarctic Surface Waters became more conducive to biological productivity with the progressive latitudinal and thermal isolation of Antarctica, The efficiency of surface productivity has progressed to such an extent that much of the global silica supply has been transferred to the Antarctic at the expense of other productive oceanic regions such as the Central Equatorial Pacific. In the Neogene, the preservation or dissolution of calcium carbonate is influenced by the rate of upwelling south of the Polar Front. During glacial times, the upwelling of COB_rich Circumpolar Deep Water accelerates and effectively raises the calcite compensation depth. Close

• 31. [Article] Origin of the Tucannon phase in Lower Snake River prehistory

  Approximately 5,500 years ago a discreet period of wetter and cooler environmental conditions prevailed across the southern Columbia Plateau. This period was marked by the first prominent episodes of erosion ...

  Citation × Citation Citation Abstract Copy Title: Origin of the Tucannon phase in Lower Snake River prehistory Author: Lucas, Steven W. Approximately 5,500 years ago a discreet period of wetter and cooler environmental conditions prevailed across the southern Columbia Plateau. This period was marked by the first prominent episodes of erosion to occur along the lower Snake River following the height of the Altithermal and eruption of Mt. Mazama during the mid post-glacial. In addition to the reactivation of small stream courses choked with debris and sediment, large stream channels began downcutting and scouring older terrace faces incorporated with large accumulations of Mazama ash. The resulting degradation of aquatic habitats forced concurrent changes within human economies adapted to the local riverine-environments. These adjustments reported for the Tucannon phase time period along the lower Snake River are notable and demonstrate the degree to which Cascade phase culture was unsuccessful in coping with environmental instability at the end of the Altithermal time period. This successionary event has demonstratively become the most significant post-glacial, qualitative change to occur in the lifeways of lower Snake River people prior to Euro-American influence. Title: Origin of the Tucannon phase in Lower Snake River prehistory Author: Lucas, Steven W. Approximately 5,500 years ago a discreet period of wetter and cooler environmental conditions prevailed across the southern Columbia Plateau. This period was marked by the first prominent episodes of erosion to occur along the lower Snake River following the height of the Altithermal and eruption of Mt. Mazama during the mid post-glacial. In addition to the reactivation of small stream courses choked with debris and sediment, large stream channels began downcutting and scouring older terrace faces incorporated with large accumulations of Mazama ash. The resulting degradation of aquatic habitats forced concurrent changes within human economies adapted to the local riverine-environments. These adjustments reported for the Tucannon phase time period along the lower Snake River are notable and demonstrate the degree to which Cascade phase culture was unsuccessful in coping with environmental instability at the end of the Altithermal time period. This successionary event has demonstratively become the most significant post-glacial, qualitative change to occur in the lifeways of lower Snake River people prior to Euro-American influence. Close

• 32. [Article] The changing glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington : implications for periglacial debris flows

  Mountain glaciers are receding worldwide with numerous consequences including changing hydrology and geomorphology. This study focuses on changes in glacier area on Mt. Hood, Oregon and Mt. Rainier, Washington ...

  Citation × Citation Citation Abstract Copy Title: The changing glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington : implications for periglacial debris flows Author: Ellinger, Jonathan R. Mountain glaciers are receding worldwide with numerous consequences including changing hydrology and geomorphology. This study focuses on changes in glacier area on Mt. Hood, Oregon and Mt. Rainier, Washington where damaging debris flows have occurred in glaciated basins. Landsat imagery is used to map debris-free ice on a decadal time scale from 1987 to 2005. Debris-free glacier ice is clearly delineated using a ratio of Landsat spectral bands in the near-infrared part of the spectrum (bands 4 & 5). Landsat scenes were chosen during the months of September and October to minimize snow cover left over from the accumulation season and maximize exposure of debris-free glacial ice. SNOTEL data were also used to find the lowest snow year for each decade to minimize the potential of misclassifying remnant snow as glacial ice. Changes in debris-free ice are mapped to produce the most up-to-date rates of glacier retreat. Average glacial slopes, derived from airborne LiDAR data are used to compute slope corrected debris-free ice areas for all glaciers. A threshold value for the Landsat NDGI scenes was selected based on threshold testing on the Eliot and Reid glaciers on Mt. Hood. Contradicting earlier studies that say the glaciers on Mt. Hood are receding faster than the glaciers on Mt. Rainier, results show that from 1987 to 2005 Mt. Rainier and Mt. Hood lost similar amounts of debris-free ice extent at 14.0% and 13.9%, respectively. For both Mt. Hood and Mt. Rainier the change in slope corrected debris-free ice area was greater than that of the projected area change due to the steep slopes of both mountains. For Mt. Rainier an increase in recession rate was shown from 1992-2005 compared to 1987-1992 while on Mt. Hood the opposite is seen. On Mt. Rainier it was found that highly fragmented glaciers at lower elevations such as the Inter, Pyramid, and the Van Trump Glaciers lost the highest percent of their original 1987 ice extent and were also shown to be associated with new debris flows in 2006. On Mt. Hood none of the 2006 debris flows initiated within zones of recent glacial recession, however, all debris flows from 2006 originated from streams with a direct connection to glaciers. The Newton Clark Glacier, having lost the most coverage of debris-free ice from 1987 to 2005, is also associated with the highest number of debris-flows in its drainage since 1980. Precipitation data for both mountains show no trend but there was a statistically significant increase in summer air temperature at Mt. Hood over the period 1984-2009. This study suggests that glaciers may play a role in the location of initiation sites, of debris flows, but there is not enough evidence to argue that glacier recession is responsible for producing debris flows. Title: The changing glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington : implications for periglacial debris flows Author: Ellinger, Jonathan R. Mountain glaciers are receding worldwide with numerous consequences including changing hydrology and geomorphology. This study focuses on changes in glacier area on Mt. Hood, Oregon and Mt. Rainier, Washington where damaging debris flows have occurred in glaciated basins. Landsat imagery is used to map debris-free ice on a decadal time scale from 1987 to 2005. Debris-free glacier ice is clearly delineated using a ratio of Landsat spectral bands in the near-infrared part of the spectrum (bands 4 & 5). Landsat scenes were chosen during the months of September and October to minimize snow cover left over from the accumulation season and maximize exposure of debris-free glacial ice. SNOTEL data were also used to find the lowest snow year for each decade to minimize the potential of misclassifying remnant snow as glacial ice. Changes in debris-free ice are mapped to produce the most up-to-date rates of glacier retreat. Average glacial slopes, derived from airborne LiDAR data are used to compute slope corrected debris-free ice areas for all glaciers. A threshold value for the Landsat NDGI scenes was selected based on threshold testing on the Eliot and Reid glaciers on Mt. Hood. Contradicting earlier studies that say the glaciers on Mt. Hood are receding faster than the glaciers on Mt. Rainier, results show that from 1987 to 2005 Mt. Rainier and Mt. Hood lost similar amounts of debris-free ice extent at 14.0% and 13.9%, respectively. For both Mt. Hood and Mt. Rainier the change in slope corrected debris-free ice area was greater than that of the projected area change due to the steep slopes of both mountains. For Mt. Rainier an increase in recession rate was shown from 1992-2005 compared to 1987-1992 while on Mt. Hood the opposite is seen. On Mt. Rainier it was found that highly fragmented glaciers at lower elevations such as the Inter, Pyramid, and the Van Trump Glaciers lost the highest percent of their original 1987 ice extent and were also shown to be associated with new debris flows in 2006. On Mt. Hood none of the 2006 debris flows initiated within zones of recent glacial recession, however, all debris flows from 2006 originated from streams with a direct connection to glaciers. The Newton Clark Glacier, having lost the most coverage of debris-free ice from 1987 to 2005, is also associated with the highest number of debris-flows in its drainage since 1980. Precipitation data for both mountains show no trend but there was a statistically significant increase in summer air temperature at Mt. Hood over the period 1984-2009. This study suggests that glaciers may play a role in the location of initiation sites, of debris flows, but there is not enough evidence to argue that glacier recession is responsible for producing debris flows. Close

• 33. [Article] Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846

  High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time ...

  Citation × Citation Citation Abstract Copy Title: Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846 Author: Shackleton, N.J., Le, J., Mix, Alan C. High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic δ¹⁸0 record to the SPECMAP and ODP Site 677 δ¹⁸0 time scales using the mapping function technique of Martinson et al. (1981). Our observations show that variations in the foraminiferal assemblages, although influenced by dissolution, are interpretable in terms of changing characteristics of upper ocean waters. Carbonate dissolution as indicated by fragmentation of planktonic foraminifers shows concentrated variance that is coherent with δ¹⁸0 at the 100 and 41 k.y. orbital periods. At these periods, maximum dissolution occurs during interglacial extremes. This finding differs from previous studies that have indicated that in this region percent carbonate minimum lags global ice volume minimum. N. dutertrei and dextral N. pachyderma dominate the assemblages, but do not show consistent relationships relative to glacial-interglacial cycles. However, less abundant species G. ruber, G. menardii, G. glutinata and G. sacculifer show positive and G. bulloides negative correlation with the δ¹⁸0 record. Q-mode factor analysis of the Site 846 assemblages and comparison with modern assemblages suggest the following. Prior to and during interglacials, the area was considerably warmer and more subtropical than at present; during glacials, the area was colder than at present with greater upwelling and advection off the eastern boundary, and possibly a stronger Peru Current; the equatorial “cool tongue” was also possibly stronger. Title: Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846 Author: Shackleton, N.J., Le, J., Mix, Alan C. High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic δ¹⁸0 record to the SPECMAP and ODP Site 677 δ¹⁸0 time scales using the mapping function technique of Martinson et al. (1981). Our observations show that variations in the foraminiferal assemblages, although influenced by dissolution, are interpretable in terms of changing characteristics of upper ocean waters. Carbonate dissolution as indicated by fragmentation of planktonic foraminifers shows concentrated variance that is coherent with δ¹⁸0 at the 100 and 41 k.y. orbital periods. At these periods, maximum dissolution occurs during interglacial extremes. This finding differs from previous studies that have indicated that in this region percent carbonate minimum lags global ice volume minimum. N. dutertrei and dextral N. pachyderma dominate the assemblages, but do not show consistent relationships relative to glacial-interglacial cycles. However, less abundant species G. ruber, G. menardii, G. glutinata and G. sacculifer show positive and G. bulloides negative correlation with the δ¹⁸0 record. Q-mode factor analysis of the Site 846 assemblages and comparison with modern assemblages suggest the following. Prior to and during interglacials, the area was considerably warmer and more subtropical than at present; during glacials, the area was colder than at present with greater upwelling and advection off the eastern boundary, and possibly a stronger Peru Current; the equatorial “cool tongue” was also possibly stronger. Close

• 34. [Article] Increased dissolved terrestrial input to the coastal ocean during the last deglaciation

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Increased dissolved terrestrial input to the coastal ocean during the last deglaciation Author: Haley, B. A., Klinkhammer, Gary P., Mix, Alan C. Copyrighted by American Geophysical Union. Title: Increased dissolved terrestrial input to the coastal ocean during the last deglaciation Author: Haley, B. A., Klinkhammer, Gary P., Mix, Alan C. Copyrighted by American Geophysical Union. Close

• 35. [Article] Sediment storage and delivery on Holocene glacial timescales, Granite Creek, southern Alaska

  Sediment storage in and release from the Granite Creek catchment over Holocene timescales is modulated by the fluctuations of Tana Glacier, which periodically blocks the outlet of Granite Creek. Little ...

  Citation × Citation Citation Abstract Copy Title: Sediment storage and delivery on Holocene glacial timescales, Granite Creek, southern Alaska Author: Blair, Mehgan O'Hearn Sediment storage in and release from the Granite Creek catchment over Holocene timescales is modulated by the fluctuations of Tana Glacier, which periodically blocks the outlet of Granite Creek. Little Ice Age expansion from 1500-1900 AD is suggested by lichenometric ages of alpine glacial moraines within Granite Creek valley. Trimlines above the Tana Glacier terminus indicate that, during this period, ice was at least 120 m thicker in the Tana Valley. According to the elevation of shorelines within the valley, the resultant ice-dammed lake occupied 50 km2 in the lower -10 km of Granite Creek valley, contained 5.9 km3 of water, and was at least 90 m deep at its maximum. Removal of the ice dam occurred during twentieth century thinning of Tana Glacier and caused a 100-m drop in the base level of Granite Creek, driving evacuation of lacustrine valley fill. The reestablishment of the fluvial system was characterized by lateral migration of Granite Creek and formation of a series of paired terraces, indicating a on-catastrophic and possibly seasonal drainage of the lake. Roughly 1.3 x 10" ms of stored sediment has been removed from the basin since drainage of the lake. Radiocarbon ages within the valley fill reveal an unconformity between overlying sediment deposited during the Little Ice Age and underlying, older sediment dating to --900 yrs B.P. Two episodes of impoundment and lacustrine deposition in the basin occurred during the mid-late Holocene and may have been separated by a period of incomplete evacuation of the valley fill. These observations reveal that sediment production within, and sediment delivery gut of this catchment are out of phase, which is characteristic of paraglacial landscape response following deglaciation. In southern Alaska, paraglacial landscape adjustment may explain the discrepancy between erosion rates estimated from short-term sediment yields and those from long-term exhumation rates. It is clear that the interpretation of sediment yields requires consideration of all sources of eroded sediment, including stored material, on a variety of timescales. Title: Sediment storage and delivery on Holocene glacial timescales, Granite Creek, southern Alaska Author: Blair, Mehgan O'Hearn Sediment storage in and release from the Granite Creek catchment over Holocene timescales is modulated by the fluctuations of Tana Glacier, which periodically blocks the outlet of Granite Creek. Little Ice Age expansion from 1500-1900 AD is suggested by lichenometric ages of alpine glacial moraines within Granite Creek valley. Trimlines above the Tana Glacier terminus indicate that, during this period, ice was at least 120 m thicker in the Tana Valley. According to the elevation of shorelines within the valley, the resultant ice-dammed lake occupied 50 km2 in the lower -10 km of Granite Creek valley, contained 5.9 km3 of water, and was at least 90 m deep at its maximum. Removal of the ice dam occurred during twentieth century thinning of Tana Glacier and caused a 100-m drop in the base level of Granite Creek, driving evacuation of lacustrine valley fill. The reestablishment of the fluvial system was characterized by lateral migration of Granite Creek and formation of a series of paired terraces, indicating a on-catastrophic and possibly seasonal drainage of the lake. Roughly 1.3 x 10" ms of stored sediment has been removed from the basin since drainage of the lake. Radiocarbon ages within the valley fill reveal an unconformity between overlying sediment deposited during the Little Ice Age and underlying, older sediment dating to --900 yrs B.P. Two episodes of impoundment and lacustrine deposition in the basin occurred during the mid-late Holocene and may have been separated by a period of incomplete evacuation of the valley fill. These observations reveal that sediment production within, and sediment delivery gut of this catchment are out of phase, which is characteristic of paraglacial landscape response following deglaciation. In southern Alaska, paraglacial landscape adjustment may explain the discrepancy between erosion rates estimated from short-term sediment yields and those from long-term exhumation rates. It is clear that the interpretation of sediment yields requires consideration of all sources of eroded sediment, including stored material, on a variety of timescales. Close

• 36. [Article] The Holocene History of Nares Strait: Transition from Glacial Bay to Arctic-Atlantic Throughflow

  This is the publisher's version of record. The original submission is copyrighted by Oceanography Society and can be found here: http://www.tos.org/

  Citation × Citation Citation Abstract Copy Title: The Holocene History of Nares Strait: Transition from Glacial Bay to Arctic-Atlantic Throughflow Author: Francus, Pierre, Sheldon, Christina, Andrews, John, Stoner, Joseph, Cronin, Thomas M., Jennings, Anne E. This is the publisher's version of record. The original submission is copyrighted by Oceanography Society and can be found here: http://www.tos.org/ Title: The Holocene History of Nares Strait: Transition from Glacial Bay to Arctic-Atlantic Throughflow Author: Francus, Pierre, Sheldon, Christina, Andrews, John, Stoner, Joseph, Cronin, Thomas M., Jennings, Anne E. This is the publisher's version of record. The original submission is copyrighted by Oceanography Society and can be found here: http://www.tos.org/ Close

• 37. [Article] Thorium-230 normalized particle flux and sediment focusing in the Panama Basin region during the last 30,000 years

  Copyright 2007 by the American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Thorium-230 normalized particle flux and sediment focusing in the Panama Basin region during the last 30,000 years Author: Francois, R., Kienast, M., Calvert, S. E., Kienast, S. S., Mix, Alan C. Copyright 2007 by the American Geophysical Union Title: Thorium-230 normalized particle flux and sediment focusing in the Panama Basin region during the last 30,000 years Author: Francois, R., Kienast, M., Calvert, S. E., Kienast, S. S., Mix, Alan C. Copyright 2007 by the American Geophysical Union Close

• 38. [Article] Eastern Pacific Warm Pool paleosalinity and climate variability: 0–30 kyr

  Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, ...

  Citation × Citation Citation Abstract Copy Title: Eastern Pacific Warm Pool paleosalinity and climate variability: 0–30 kyr Author: Haley, Brian A., Benway, Heather M., Mix, Alan C., Klinkhammer, Gary P. Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 kyr. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 practical salinity units occur with a dominant period of ~3–5 ky during the glacial/deglacial interval and ~1.0–1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively. Title: Eastern Pacific Warm Pool paleosalinity and climate variability: 0–30 kyr Author: Haley, Brian A., Benway, Heather M., Mix, Alan C., Klinkhammer, Gary P. Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 kyr. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 practical salinity units occur with a dominant period of ~3–5 ky during the glacial/deglacial interval and ~1.0–1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively. Close

• 39. [Article] Geology of the Whetstone anticline area, Teton County Wyoming

  Over 10,000 feet of marine and nonmarine Late Cretaceous sedimentary rocks are exposed within a 110 square mile area in northeastern Teton County, Wyoming. An additional 1400 feet of nonmarine Paleocene ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Whetstone anticline area, Teton County Wyoming Author: Hill, David Ray Over 10,000 feet of marine and nonmarine Late Cretaceous sedimentary rocks are exposed within a 110 square mile area in northeastern Teton County, Wyoming. An additional 1400 feet of nonmarine Paleocene and Miocene rocks overlie these. Landslide deposits and Pleistocene glacial moraine cover over one-half of the area. The Late Cretaceous Cody Shale and Bacon Ridge Sandstone, which are the oldest rocks exposed, represent the last marine invasion of the region. The overlying Late Cretaceous nonmarine rocks consist of the Coaly Sequence, Lenticular Sandstone and Shale Sequence, Mesaverde Formation, and Harebell Formation. These formations are composed largely of poorly sorted quartz arenites with intercalated mudstones, claystones, shales, and coals. A few quartzite conglomerate lenses are present near the top of the sequence. These rocks, which contain numerous quartz, chert, and metaquartzite grains, were derived from Precambrian metamorphic and Paleozoic sedimentary rocks exposed to the west and northwest. The sediments were carried into the area by streams and were deposited on a broad coastal plain similar to the modern Texas Gulf Coast. Many of the fine-grained sediments were deposited in swamps and small freshwater lakes. Near the end of Cretaceous time, a large area of Precambrian Beltian quartzite was exposed in central Montana. Powerful streams carried large volumes of coarse sediments into the area mapped forming the Paleocene Pinyon Conglomerate. Basalt and andesite were extruded locally during the Miocene. Morainal deposits from two Pleistocene glacial stages are recognized. Two periods of Laramide deformation are represented by broad asymmetric folds. The Spread Creek anticline, a large doubly plunging fold, was formed near the end of Cretaceous time. Three adjacent folds to the northeast are post-Paleocene in age. Several high-angle faults are present. Structural and stratigraphic conditions appear to be favorable for the formation and accumulation of oil and gas. However, five dry oil and gas test holes have been drilled. The possibilities of finding commercial production are not encouraging. The area has also been prospected for coal and alluvial gold. Title: Geology of the Whetstone anticline area, Teton County Wyoming Author: Hill, David Ray Over 10,000 feet of marine and nonmarine Late Cretaceous sedimentary rocks are exposed within a 110 square mile area in northeastern Teton County, Wyoming. An additional 1400 feet of nonmarine Paleocene and Miocene rocks overlie these. Landslide deposits and Pleistocene glacial moraine cover over one-half of the area. The Late Cretaceous Cody Shale and Bacon Ridge Sandstone, which are the oldest rocks exposed, represent the last marine invasion of the region. The overlying Late Cretaceous nonmarine rocks consist of the Coaly Sequence, Lenticular Sandstone and Shale Sequence, Mesaverde Formation, and Harebell Formation. These formations are composed largely of poorly sorted quartz arenites with intercalated mudstones, claystones, shales, and coals. A few quartzite conglomerate lenses are present near the top of the sequence. These rocks, which contain numerous quartz, chert, and metaquartzite grains, were derived from Precambrian metamorphic and Paleozoic sedimentary rocks exposed to the west and northwest. The sediments were carried into the area by streams and were deposited on a broad coastal plain similar to the modern Texas Gulf Coast. Many of the fine-grained sediments were deposited in swamps and small freshwater lakes. Near the end of Cretaceous time, a large area of Precambrian Beltian quartzite was exposed in central Montana. Powerful streams carried large volumes of coarse sediments into the area mapped forming the Paleocene Pinyon Conglomerate. Basalt and andesite were extruded locally during the Miocene. Morainal deposits from two Pleistocene glacial stages are recognized. Two periods of Laramide deformation are represented by broad asymmetric folds. The Spread Creek anticline, a large doubly plunging fold, was formed near the end of Cretaceous time. Three adjacent folds to the northeast are post-Paleocene in age. Several high-angle faults are present. Structural and stratigraphic conditions appear to be favorable for the formation and accumulation of oil and gas. However, five dry oil and gas test holes have been drilled. The possibilities of finding commercial production are not encouraging. The area has also been prospected for coal and alluvial gold. Close

• 40. [Article] Palynological Perspectives on Younger Dryas to Early Holocene Human Ecology at Paisley Caves, Oregon

  The Younger Dryas climatic event is a global phenomenon associated with a 1,000 year return to glacial conditions during the late Pleistocene period between 12,800 and 11,500 cal BP. Because of its significant ...

  Citation × Citation Citation Abstract Copy Title: Palynological Perspectives on Younger Dryas to Early Holocene Human Ecology at Paisley Caves, Oregon Author: Saban, Chantel V. The Younger Dryas climatic event is a global phenomenon associated with a 1,000 year return to glacial conditions during the late Pleistocene period between 12,800 and 11,500 cal BP. Because of its significant effects on paleoenvironmental conditions in some parts of the world, archaeologists commonly seek to assess whether the Younger Dryas climatic event had any measureable influence on prehistoric human societies. The early, well preserved archaeological and paleoenvironmental records held in the Paisley Caves site of Oregon's Northern Great Basin provide an opportunity to examine questions human-environmental interaction at the end of the Pleistocene Epoch. Based on a study of pollen records and artifact frequency in the site's Cave 2 deposits, this thesis reports a positive relationship between artifact deposition and marsh expansion in the Summer Lake sub-basin during the Younger Dryas chronozone. While not indicative of a major change in early forager cultural patterns in the Northern Great Basin, these results provide an important perspective on early settlement patterns and human ecology in the far western region of North America. Title: Palynological Perspectives on Younger Dryas to Early Holocene Human Ecology at Paisley Caves, Oregon Author: Saban, Chantel V. The Younger Dryas climatic event is a global phenomenon associated with a 1,000 year return to glacial conditions during the late Pleistocene period between 12,800 and 11,500 cal BP. Because of its significant effects on paleoenvironmental conditions in some parts of the world, archaeologists commonly seek to assess whether the Younger Dryas climatic event had any measureable influence on prehistoric human societies. The early, well preserved archaeological and paleoenvironmental records held in the Paisley Caves site of Oregon's Northern Great Basin provide an opportunity to examine questions human-environmental interaction at the end of the Pleistocene Epoch. Based on a study of pollen records and artifact frequency in the site's Cave 2 deposits, this thesis reports a positive relationship between artifact deposition and marsh expansion in the Summer Lake sub-basin during the Younger Dryas chronozone. While not indicative of a major change in early forager cultural patterns in the Northern Great Basin, these results provide an important perspective on early settlement patterns and human ecology in the far western region of North America. Close

• 41. [Article] Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho

  The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been ...

  Citation × Citation Citation Abstract Copy Title: Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho Author: Moran, John Lee The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been divided into 23 mapped units. Pre-Belt metamorphic basement rocks are overlain unconformably by 3,433 feet of Paleozoic strata included in eleven formations. These formations represent all of the periods of the Paleozoic except the Ordovician and Silurian. Nine formations represent all the periods of the Mesozoic and total approximately 3,127 feet in thickness. Cenozoic units present in the area are basalts and rhyolites, landslide debris, glacial deposits, and alluvium. The major structure of the thesis area is a fault block that is the result of uplifting and tilting of the east-west trending Centennial Range during the downwarp of the Snake River Plain in late Pliocene and Pleistocene time. No stratigraphic or structural conditions in the thesis area are favorable for the accumulation and entrapment of oil and gas. Phosphorite has been mined from the Phosphoria Formation in the area. Title: Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho Author: Moran, John Lee The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been divided into 23 mapped units. Pre-Belt metamorphic basement rocks are overlain unconformably by 3,433 feet of Paleozoic strata included in eleven formations. These formations represent all of the periods of the Paleozoic except the Ordovician and Silurian. Nine formations represent all the periods of the Mesozoic and total approximately 3,127 feet in thickness. Cenozoic units present in the area are basalts and rhyolites, landslide debris, glacial deposits, and alluvium. The major structure of the thesis area is a fault block that is the result of uplifting and tilting of the east-west trending Centennial Range during the downwarp of the Snake River Plain in late Pliocene and Pleistocene time. No stratigraphic or structural conditions in the thesis area are favorable for the accumulation and entrapment of oil and gas. Phosphorite has been mined from the Phosphoria Formation in the area. Close

• 42. [Article] Late Quaternary sedimentation and geologic history of the North Willamette Valley, Oregon

  Late Quaternary sediments in the Willamette Valley, Oregon, include a unit of chiefly silt and fine sand, the Willamette Silt Formation. Previous workers have (1) Assigned the Willamette Silt different ...

  Citation × Citation Citation Abstract Copy Title: Late Quaternary sedimentation and geologic history of the North Willamette Valley, Oregon Author: Glenn, Jerry L. Late Quaternary sediments in the Willamette Valley, Oregon, include a unit of chiefly silt and fine sand, the Willamette Silt Formation. Previous workers have (1) Assigned the Willamette Silt different ages which range from Sangamon interglacial to late Wisconsin glacial, (2) Proposed that the Willamette Silt was deposited in a ponded body of water which was produced by (a) a tectonic rise in sea level, (b) icejam dams, (c) a eustatic rise in sea level, or (d) a "hydraulic dam", (3) Attributed the Willamette Silt to (a) one catastrophic flood- -the Spokane Flood- -in the Columbia River Valley, (b) "normal" Columbia River floods supplemented by locally derived sediments, or (c) multiple large Columbia River floods. The petrography and stratigraphy of the Willamette Silt and the geomorphology of the Willamette Silt surface have been investigated in the north Willamette Valley. The results of these investigations and the results of a radiocarbon dating program provide data for a new interpretation of the nature and sequence of late Quaternary geologic events in the Willamette and Columbia Valleys. Petrography establishes: (1) that the Willamette Silt was not derived from the local Willamette Valley provenance, (2) that sediments mineralogically similar to the Willamette Silt are present in the Columbia Valley and in the Yakima and Walla Walla Valleys of southeastern Washington, and (3) that the Willamette Silt contains no more locally derived heavy minerals than Columbia River sediment contains. Stratigraphy indicates: (1) that the Willamette Silt unconformably overlies weathered Tertiary bedrock and older Quaternary glacial outwash on the valley margins, (2) that the silt conformably overlies locally derived fluvial-lacustrine sediments in deep central parts of the valley and conformably overlies young glacio-fluvial fan gravels, (3) that deposition of the silt was accomplished during at least 40 large Columbia River floods into the Willamette Valley, (4) that these floods carried heavy loads of chiefly silt and fine sand, (5) that the silt, at least at lower altitudes, was emplaced in a continuously ponded water during a geologically short time span, and (6) that ponded water was not stable at any altitude for long periods of time and that it drained rapidly from the Willamette Valley. Geomorphology of the Willamette Silt surface shows:(1) that deposition of the Willamette Silt was followed by rapid stream entrenchment, (2) that a climactic Columbia River flood, larger than previous floods, entered the Willamette Valley after subaerial weathering and erosion of the Willamette Silt. Stratigraphy, geomorphology, and radiocarbon dates show: (1) that the last Cascade Mountains glaciation that resulted in a significant aggradation by Willamette River tributaries began more than 34,410 ± 3,450 years before present (B.P.), (2) that the last climactic flood occurred about 19,000 years (B. P.), and (3) that the age of the Willamette Silt is between 19,000 years (B.P.) and 34, 410 ± 3,450 years (B.P.). The writer proposes: (1) that flooding was caused by repeated failures of the Lake Missoula glacial ice darn northeast of the channeled scablands, (2) that floods, which sequentially eroded scabland tracts, scoured the Palouse Formation sediments from the scabland tracts, and redeposited part of the sediments in the Columbia River Valley and in major tributary valleys, and (3) that ponded water was maintained in the Willamette Valley by more rapid aggradation in the Columbia Valley than in the Willamette Valley. Title: Late Quaternary sedimentation and geologic history of the North Willamette Valley, Oregon Author: Glenn, Jerry L. Late Quaternary sediments in the Willamette Valley, Oregon, include a unit of chiefly silt and fine sand, the Willamette Silt Formation. Previous workers have (1) Assigned the Willamette Silt different ages which range from Sangamon interglacial to late Wisconsin glacial, (2) Proposed that the Willamette Silt was deposited in a ponded body of water which was produced by (a) a tectonic rise in sea level, (b) icejam dams, (c) a eustatic rise in sea level, or (d) a "hydraulic dam", (3) Attributed the Willamette Silt to (a) one catastrophic flood- -the Spokane Flood- -in the Columbia River Valley, (b) "normal" Columbia River floods supplemented by locally derived sediments, or (c) multiple large Columbia River floods. The petrography and stratigraphy of the Willamette Silt and the geomorphology of the Willamette Silt surface have been investigated in the north Willamette Valley. The results of these investigations and the results of a radiocarbon dating program provide data for a new interpretation of the nature and sequence of late Quaternary geologic events in the Willamette and Columbia Valleys. Petrography establishes: (1) that the Willamette Silt was not derived from the local Willamette Valley provenance, (2) that sediments mineralogically similar to the Willamette Silt are present in the Columbia Valley and in the Yakima and Walla Walla Valleys of southeastern Washington, and (3) that the Willamette Silt contains no more locally derived heavy minerals than Columbia River sediment contains. Stratigraphy indicates: (1) that the Willamette Silt unconformably overlies weathered Tertiary bedrock and older Quaternary glacial outwash on the valley margins, (2) that the silt conformably overlies locally derived fluvial-lacustrine sediments in deep central parts of the valley and conformably overlies young glacio-fluvial fan gravels, (3) that deposition of the silt was accomplished during at least 40 large Columbia River floods into the Willamette Valley, (4) that these floods carried heavy loads of chiefly silt and fine sand, (5) that the silt, at least at lower altitudes, was emplaced in a continuously ponded water during a geologically short time span, and (6) that ponded water was not stable at any altitude for long periods of time and that it drained rapidly from the Willamette Valley. Geomorphology of the Willamette Silt surface shows:(1) that deposition of the Willamette Silt was followed by rapid stream entrenchment, (2) that a climactic Columbia River flood, larger than previous floods, entered the Willamette Valley after subaerial weathering and erosion of the Willamette Silt. Stratigraphy, geomorphology, and radiocarbon dates show: (1) that the last Cascade Mountains glaciation that resulted in a significant aggradation by Willamette River tributaries began more than 34,410 ± 3,450 years before present (B.P.), (2) that the last climactic flood occurred about 19,000 years (B. P.), and (3) that the age of the Willamette Silt is between 19,000 years (B.P.) and 34, 410 ± 3,450 years (B.P.). The writer proposes: (1) that flooding was caused by repeated failures of the Lake Missoula glacial ice darn northeast of the channeled scablands, (2) that floods, which sequentially eroded scabland tracts, scoured the Palouse Formation sediments from the scabland tracts, and redeposited part of the sediments in the Columbia River Valley and in major tributary valleys, and (3) that ponded water was maintained in the Willamette Valley by more rapid aggradation in the Columbia Valley than in the Willamette Valley. Close

• 43. [Article] Lacustrine micro-fossil assemblage in core NP04-KH3, a Kullenberg piston core from the Moba-Kalya Horst region of Lake Tanganyika, East Africa, as a biogeochemical proxy for Late Pleistocene and Early Holocene climate and lake level changes

  The objective of this research is to determine the correlation of lacustrine micro-fossils in Lake Tanganyika to changes in climate and lake levels during the Late Pleistocene and Early Holocene. Lake ...

  Citation × Citation Citation Abstract Copy Title: Lacustrine micro-fossil assemblage in core NP04-KH3, a Kullenberg piston core from the Moba-Kalya Horst region of Lake Tanganyika, East Africa, as a biogeochemical proxy for Late Pleistocene and Early Holocene climate and lake level changes Author: Steinkamp, Matthew J. The objective of this research is to determine the correlation of lacustrine micro-fossils in Lake Tanganyika to changes in climate and lake levels during the Late Pleistocene and Early Holocene. Lake Tanganyika is the second deepest and one of the oldest lakes in the world. The horst and graben geometry of the lake has created subaqueous structural platforms that accumulate pelagic sediments that contain and archive changes in micro-fossil assemblages controlled by changes in climate and lake levels. One such structural platform is the Moba-Kalya Horst. Micro-fossil analysis of lacustrine sediments from a single Kullenberg piston core from the Moba-Kalya Horst indicate dramatic Late Pleistocene and Early Holocene climate and lake level changes that appear to be synchronized with regional, as well as hemispherical climate shifts. During the Late Pleistocene at the Last Glacial Maximum which ended approximately 15 ky B.P., Lake Tanganyika experienced low-lake stands of 250-350 meters or more below the present lake level. From 17,537 to 15,000 calendar years BP, periphytic diatoms such as Rhopalodia gibberula and Surirella fuellebornii were abundant, as were grass phytoliths and sponge spicules, indicative of a dry climate regime. The dominant planktonic diatom was Stephanodiscus astraea, which thrived in low Si:P supply ratio, stratified lake environments in Na-HCO3 rich waters, indicative of a cool, arid climate regime. Periphytic diatoms were also abundant in Lake Malawi to the south and significantly negative δ180 values were recorded in Greenland ice cores for this period. Following the low-lake stands of the Late Glacial Maximum, lake levels generally rose as East Africa experienced the AHP (African Humid Period) (14.4-5.5 cal ky BP). An increase in planktonic diatoms and decrease in periphytic diatoms were recorded in the lacustrine sediments at this time which indicate a positive water balance and rising lake levels. The accumulation of dark-bundled, laminated sediments indicate that the climate was wet and the coring site was below the annual thermocline. A decrease in S. astraea and increase in Cyclostephanos damasii signal conditions of increased moisture to the lake, and decreased evaporation. Around 13 ky B.P. conditions at Lake Tanganyika reverted to Late Glacial Maximum conditions which lasted until approximately 11.5 ky B.P.. Periphytic diatoms once again became abundant, and sponge spicule and grass phytolith counts rose. S.astraea dominance again rose as lake conditions were calm and stratified and the climate was cool and arid. Periphytic diatoms became abundant in Lake Malawi during this period, and increased negative δ180 values were recorded in the Greenland ice cores correlating with increased periphytic diatoms in both Lake Tanganyika and Lake Malawi. Following the Late Pleistocene cold period, lake levels once again began rising as the climate became wetter and windier. Fluctuations from wet and windy to wet and calm occurred at the terminus of the Late Pleistocene as diatom dominance alternated from Aulacoseira granulata, which indicates wet and windy with increase upwelling, to C.damasii, which indicate wet and stratified. Around 9800 B.P. lake conditions stabilized and remained wet and windy with increase turbulence and upwelling which optimized conditions for the dominance of A.granulata. These conditions prevailed through the Early Holocene to at least 6500 B.P. From the Middle Holocene to the present, the general climate of East Africa was and is more arid than the early Holocene, with dry windy conditions and continued upwelling. Title: Lacustrine micro-fossil assemblage in core NP04-KH3, a Kullenberg piston core from the Moba-Kalya Horst region of Lake Tanganyika, East Africa, as a biogeochemical proxy for Late Pleistocene and Early Holocene climate and lake level changes Author: Steinkamp, Matthew J. The objective of this research is to determine the correlation of lacustrine micro-fossils in Lake Tanganyika to changes in climate and lake levels during the Late Pleistocene and Early Holocene. Lake Tanganyika is the second deepest and one of the oldest lakes in the world. The horst and graben geometry of the lake has created subaqueous structural platforms that accumulate pelagic sediments that contain and archive changes in micro-fossil assemblages controlled by changes in climate and lake levels. One such structural platform is the Moba-Kalya Horst. Micro-fossil analysis of lacustrine sediments from a single Kullenberg piston core from the Moba-Kalya Horst indicate dramatic Late Pleistocene and Early Holocene climate and lake level changes that appear to be synchronized with regional, as well as hemispherical climate shifts. During the Late Pleistocene at the Last Glacial Maximum which ended approximately 15 ky B.P., Lake Tanganyika experienced low-lake stands of 250-350 meters or more below the present lake level. From 17,537 to 15,000 calendar years BP, periphytic diatoms such as Rhopalodia gibberula and Surirella fuellebornii were abundant, as were grass phytoliths and sponge spicules, indicative of a dry climate regime. The dominant planktonic diatom was Stephanodiscus astraea, which thrived in low Si:P supply ratio, stratified lake environments in Na-HCO3 rich waters, indicative of a cool, arid climate regime. Periphytic diatoms were also abundant in Lake Malawi to the south and significantly negative δ180 values were recorded in Greenland ice cores for this period. Following the low-lake stands of the Late Glacial Maximum, lake levels generally rose as East Africa experienced the AHP (African Humid Period) (14.4-5.5 cal ky BP). An increase in planktonic diatoms and decrease in periphytic diatoms were recorded in the lacustrine sediments at this time which indicate a positive water balance and rising lake levels. The accumulation of dark-bundled, laminated sediments indicate that the climate was wet and the coring site was below the annual thermocline. A decrease in S. astraea and increase in Cyclostephanos damasii signal conditions of increased moisture to the lake, and decreased evaporation. Around 13 ky B.P. conditions at Lake Tanganyika reverted to Late Glacial Maximum conditions which lasted until approximately 11.5 ky B.P.. Periphytic diatoms once again became abundant, and sponge spicule and grass phytolith counts rose. S.astraea dominance again rose as lake conditions were calm and stratified and the climate was cool and arid. Periphytic diatoms became abundant in Lake Malawi during this period, and increased negative δ180 values were recorded in the Greenland ice cores correlating with increased periphytic diatoms in both Lake Tanganyika and Lake Malawi. Following the Late Pleistocene cold period, lake levels once again began rising as the climate became wetter and windier. Fluctuations from wet and windy to wet and calm occurred at the terminus of the Late Pleistocene as diatom dominance alternated from Aulacoseira granulata, which indicates wet and windy with increase upwelling, to C.damasii, which indicate wet and stratified. Around 9800 B.P. lake conditions stabilized and remained wet and windy with increase turbulence and upwelling which optimized conditions for the dominance of A.granulata. These conditions prevailed through the Early Holocene to at least 6500 B.P. From the Middle Holocene to the present, the general climate of East Africa was and is more arid than the early Holocene, with dry windy conditions and continued upwelling. Close

• 44. [Article] Late-quaternary stratigraphy, pedology and paleoclimatic reconstruction of the Cremer Site (24SW264), south-central Montana : a geographical case study

  This study utilizes a multidisciplinary research approach integrating the sciences of archaeology, geology, pedology and paleoclimatology. Deeply stratified and radiocarbon dated sedimentary sequences ...

  Citation × Citation Citation Abstract Copy Title: Late-quaternary stratigraphy, pedology and paleoclimatic reconstruction of the Cremer Site (24SW264), south-central Montana : a geographical case study Author: White, Dustin This study utilizes a multidisciplinary research approach integrating the sciences of archaeology, geology, pedology and paleoclimatology. Deeply stratified and radiocarbon dated sedimentary sequences spanning the last 10,000 yr B.P. are reported for the Cremer site (24SW264), south-central Montana. Previous investigations at the site revealed an archaeological assemblage with Early Plains Archaic through Late Prehistoric period affiliations. Expanded testing of the site integrates the existing cultural record with new data pertaining to Holocene environmental changes at this northwestern Great Plains locality. Detailed pedological descriptions were made along three trenches excavated at the site. The combined soil-stratigraphic record indicates that distinct intervals of relative landscape stability and soil development occurred at the site at ca. 10,000 yr B.P., 7,500 yr B.P. and intermittently throughout the last ca. 6,000 yr B.P. Periods of significant landscape instability (upland erosion and valley deposition) occurred immediately following each of the early Holocene soil forming intervals identified above, and episodically throughout the middle to late Holocene. The impetus for early Holocene environmental instability is attributed to generally increased aridity on the northwestern Great Plains. Comparative analyses of site data with both regional environmental proxy records and numerical models of past climates (General Circulation and Archaeoclimatic models) are made to test the findings from the Cremer site. The collective paleoenvironmental evidence indicates that the period of maximum post-glacial warming and aridity occurred at the Cremer site during the early Holocene period (prior to ca. 6,000 yr B.P.). These data also indicate that the existing archaeological assemblage from the site is younger than ca. 6,000 yr B.P., although future excavations may reveal cultural sequences associated with the earliest dated soils at the site. This geoarchaeological study of the Cremer site should contribute to a much needed research base in this sparsely studied region. Title: Late-quaternary stratigraphy, pedology and paleoclimatic reconstruction of the Cremer Site (24SW264), south-central Montana : a geographical case study Author: White, Dustin This study utilizes a multidisciplinary research approach integrating the sciences of archaeology, geology, pedology and paleoclimatology. Deeply stratified and radiocarbon dated sedimentary sequences spanning the last 10,000 yr B.P. are reported for the Cremer site (24SW264), south-central Montana. Previous investigations at the site revealed an archaeological assemblage with Early Plains Archaic through Late Prehistoric period affiliations. Expanded testing of the site integrates the existing cultural record with new data pertaining to Holocene environmental changes at this northwestern Great Plains locality. Detailed pedological descriptions were made along three trenches excavated at the site. The combined soil-stratigraphic record indicates that distinct intervals of relative landscape stability and soil development occurred at the site at ca. 10,000 yr B.P., 7,500 yr B.P. and intermittently throughout the last ca. 6,000 yr B.P. Periods of significant landscape instability (upland erosion and valley deposition) occurred immediately following each of the early Holocene soil forming intervals identified above, and episodically throughout the middle to late Holocene. The impetus for early Holocene environmental instability is attributed to generally increased aridity on the northwestern Great Plains. Comparative analyses of site data with both regional environmental proxy records and numerical models of past climates (General Circulation and Archaeoclimatic models) are made to test the findings from the Cremer site. The collective paleoenvironmental evidence indicates that the period of maximum post-glacial warming and aridity occurred at the Cremer site during the early Holocene period (prior to ca. 6,000 yr B.P.). These data also indicate that the existing archaeological assemblage from the site is younger than ca. 6,000 yr B.P., although future excavations may reveal cultural sequences associated with the earliest dated soils at the site. This geoarchaeological study of the Cremer site should contribute to a much needed research base in this sparsely studied region. Close

• 45. [Article] Geology of the Whetstone Ridge area, Meagher County, Montana

  The thesis area consists of 65 square miles located in the southeastern part of Meagher County, Montana. Ranging in age from Precambrian to Quaternary, the strata exposed in the area have a total thickness ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Whetstone Ridge area, Meagher County, Montana Author: Glasheen, Richard Michael The thesis area consists of 65 square miles located in the southeastern part of Meagher County, Montana. Ranging in age from Precambrian to Quaternary, the strata exposed in the area have a total thickness of about 11,100 feet. Low grade metamorphic rocks, mainly slates, and limestones represent the estimated 2,000 foot thick Precambrian unit. Paleozoic rocks, about 2,600 feet in thickness, consist mainly of carbonates but include marine sandstones, some of which were metamorphosed into quartzites. Ordovician, Silurian, and Permian strata are absent. The Mesozoic rocks are dominantly marine, continental, and lacustrjne sandstones, siltstones, and shales. Rocks of Triassic age are not present in this 6, 500 foot thick sequence of sedimentary rocks. Intrusive and extrusive igneous rocks, glacial deposits, and unconsolidated alluvium represent the Cenozoic Period. The major structures in the thesis area are the result of the Lararnide Revolution and date from Late Cretaceous to Early Tertiary. Title: Geology of the Whetstone Ridge area, Meagher County, Montana Author: Glasheen, Richard Michael The thesis area consists of 65 square miles located in the southeastern part of Meagher County, Montana. Ranging in age from Precambrian to Quaternary, the strata exposed in the area have a total thickness of about 11,100 feet. Low grade metamorphic rocks, mainly slates, and limestones represent the estimated 2,000 foot thick Precambrian unit. Paleozoic rocks, about 2,600 feet in thickness, consist mainly of carbonates but include marine sandstones, some of which were metamorphosed into quartzites. Ordovician, Silurian, and Permian strata are absent. The Mesozoic rocks are dominantly marine, continental, and lacustrjne sandstones, siltstones, and shales. Rocks of Triassic age are not present in this 6, 500 foot thick sequence of sedimentary rocks. Intrusive and extrusive igneous rocks, glacial deposits, and unconsolidated alluvium represent the Cenozoic Period. The major structures in the thesis area are the result of the Lararnide Revolution and date from Late Cretaceous to Early Tertiary. Close

• 46. [Article] Stratigraphy and structure of part of the southern Madison Range, Madison and Gallatin Counties, Montana

  The thesis area consists of 42 square miles located in Madison and Gallatin counties, Montana, in the southern part of the Madison Range. The strata exposed in the area range in age from Precambrian to ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy and structure of part of the southern Madison Range, Madison and Gallatin Counties, Montana Author: Rosé, Robert Rowland The thesis area consists of 42 square miles located in Madison and Gallatin counties, Montana, in the southern part of the Madison Range. The strata exposed in the area range in age from Precambrian to Quaternary and have an aggregate thickness of more than 7,600 feet. The Paleozoic rocks, about 3,900 feet thick, are mainly carbonates but include sandstones, shales, and cherts of marine origin. Ordovician and Silurian formations are absent. The Mesozoic rocks consist mainly of sandstones, shales, calcareous claystones, and argillaceous limestones of marine and continental origin. All Mesozoic periods are represented in this 3700 foot thick sequence of sedimentary rocks. The Cenozoic rocks and sediments include welded tuff, glacial deposits, and alluvium. Quaternary landslides cover about one-quarter of the thesis area. The structures are Late Cretaceous to Early Tertiary (Laramide) and Late Cenozoic in age. The Laramide structures are northwest- trending, asymmetrical (steeper to the northeast) folds and high angle reverse faults. The Late Cenozoic structures are normal faults that displace Upper Cretaceous strata. Title: Stratigraphy and structure of part of the southern Madison Range, Madison and Gallatin Counties, Montana Author: Rosé, Robert Rowland The thesis area consists of 42 square miles located in Madison and Gallatin counties, Montana, in the southern part of the Madison Range. The strata exposed in the area range in age from Precambrian to Quaternary and have an aggregate thickness of more than 7,600 feet. The Paleozoic rocks, about 3,900 feet thick, are mainly carbonates but include sandstones, shales, and cherts of marine origin. Ordovician and Silurian formations are absent. The Mesozoic rocks consist mainly of sandstones, shales, calcareous claystones, and argillaceous limestones of marine and continental origin. All Mesozoic periods are represented in this 3700 foot thick sequence of sedimentary rocks. The Cenozoic rocks and sediments include welded tuff, glacial deposits, and alluvium. Quaternary landslides cover about one-quarter of the thesis area. The structures are Late Cretaceous to Early Tertiary (Laramide) and Late Cenozoic in age. The Laramide structures are northwest- trending, asymmetrical (steeper to the northeast) folds and high angle reverse faults. The Late Cenozoic structures are normal faults that displace Upper Cretaceous strata. Close

• 47. [Article] Calcium carbonate, organic carbon, and quartz in hemipelagic sediments off Oregon : a preliminary investigation

  An analysis of the amounts of calcium carbonate, organic carbon, quartz, and the rates of sediment accumulation in hemipelagic sediments off Oregon has revealed that the accumulation rates of the total sediment, ...

  Citation × Citation Citation Abstract Copy Title: Calcium carbonate, organic carbon, and quartz in hemipelagic sediments off Oregon : a preliminary investigation Author: Peterson, Robert E. An analysis of the amounts of calcium carbonate, organic carbon, quartz, and the rates of sediment accumulation in hemipelagic sediments off Oregon has revealed that the accumulation rates of the total sediment, organic carbon, and quartz were at least twice as high in the late Pleistocene as they were during the Holocene. The accumulation rate of calcium carbonate was at least 8 times as high. There may have been a short transition period at the end of the last glacial stage from about 14,000 to 12,500 years B.P. when the sedimentation rate was very high up to 75 cm/l000 years. There is evidence that the amount of organic carbon in deep-sea sediments is a function of terrigenous influx, of preservation, and possibly of depth of burial in the sediment. Turbidite sequences in the deep-sea environment off Oregon contain much higher amounts of organic carbon in the upper fine-grained portion of the sequence than in the coarser basal sediment of the sequence, indicating that organic carbon is concentrated in the finer and slower settling parts of the flow. In lower continental slope sediments, the greatest amounts of organic carbon are found in the <4 micron size fraction. Title: Calcium carbonate, organic carbon, and quartz in hemipelagic sediments off Oregon : a preliminary investigation Author: Peterson, Robert E. An analysis of the amounts of calcium carbonate, organic carbon, quartz, and the rates of sediment accumulation in hemipelagic sediments off Oregon has revealed that the accumulation rates of the total sediment, organic carbon, and quartz were at least twice as high in the late Pleistocene as they were during the Holocene. The accumulation rate of calcium carbonate was at least 8 times as high. There may have been a short transition period at the end of the last glacial stage from about 14,000 to 12,500 years B.P. when the sedimentation rate was very high up to 75 cm/l000 years. There is evidence that the amount of organic carbon in deep-sea sediments is a function of terrigenous influx, of preservation, and possibly of depth of burial in the sediment. Turbidite sequences in the deep-sea environment off Oregon contain much higher amounts of organic carbon in the upper fine-grained portion of the sequence than in the coarser basal sediment of the sequence, indicating that organic carbon is concentrated in the finer and slower settling parts of the flow. In lower continental slope sediments, the greatest amounts of organic carbon are found in the <4 micron size fraction. Close

• 48. [Article] Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years

  Access to this item has been restricted by repository administrators at the request of the publisher until October 28, 2016.

  Citation × Citation Citation Abstract Copy Title: Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years Author: Steig, Eric J., Fudge, T. J., Buizert, Christo, Markle, Bradley R., Taylor, Kendrick C., Cuffey, Kurt M., Waddington, Edwin D., Koutnik, Michelle, Conway, Howard Access to this item has been restricted by repository administrators at the request of the publisher until October 28, 2016. Title: Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years Author: Steig, Eric J., Fudge, T. J., Buizert, Christo, Markle, Bradley R., Taylor, Kendrick C., Cuffey, Kurt M., Waddington, Edwin D., Koutnik, Michelle, Conway, Howard Access to this item has been restricted by repository administrators at the request of the publisher until October 28, 2016. Close

• 49. [Article] Simulating past, present, and future changes in ENSO : a model evaluation and data-model comparison

  This thesis presents the results of a formal evaluation of a new AOGCM, GENMOM, demonstrating its ability to simulate present-day climate and ENSO dynamics. The model is applied to simulate climate for ...

  Citation × Citation Citation Abstract Copy Title: Simulating past, present, and future changes in ENSO : a model evaluation and data-model comparison Author: Alder, Jay R. This thesis presents the results of a formal evaluation of a new AOGCM, GENMOM, demonstrating its ability to simulate present-day climate and ENSO dynamics. The model is applied to simulate climate for the Last Glacial Maximum, deglacial, and Holocene time periods. The model output is evaluated against the best available proxy reconstructions in a detailed data-model comparison. ENSO strength is analyzed in seven paleo simulations and compared to coral and laminated lake sediment proxy records to provide an understanding of how ENSO related mechanisms varied in the past and how they vary under increased atmospheric CO₂ forced global warming. The GENMOM simulated present-day is found to be on par with three models used in the IPCC AR4 assessment and is comparable with reanalysis products (e.g, NCEP2). Atmospheric features such as the jet stream structure and major semipermanent sea level pressure centers are well simulated as is the mean planetary-scale wind structure that is needed to produce the correct position of stormtracks. Most ocean surface currents are reproduced except where they are not resolvable at T31 resolution. Overall, GENMOM captures the observed gradients and spatial distributions of annual surface temperature and precipitation and the simulations are on par with other AOGCMs. Deficiencies in the GENMOM present-day simulation include a warm bias in the surface temperature over the southern oceans, a split in the ITCZ and weaker-thanobserved overturning circulation. GENMOM produces a global temperature bias of 0.6 °C. GENMOM is demonstrated to capture ENSO dynamics similar to eight AOGCMs that were evaluated in the IPCC AR4. The Niño 3 - 4 indices have a standard deviation within 0.3 °C of the observations, indicating GENMOM is producing variability in the tropical Pacifc that is comparable to observations. GENMOM produces present-day ENSO events with an average period of 5.6 years, which is within the 2 – 7 range exhibited in the observed historical record. The mid-Holocene (6ka) and Last Glacial Maximum (LGM, 21ka) simulations are compared to the best available proxy reconstructions for sea surface temperature, precipitation and net moisture to ensure the simulations are plausible. This thesis finds that the model is in good agreement over broad spatial scales, with regional discrepancies between the model and proxy data. Coral and laminated lake sediment proxy records indicate mid-Holocene ENSO strength was reduced by 15 - 60%, offering a scenario in which ENSO-related components can be tested in climates different than present-day, thereby providing context for future changes in ENSO. The mid-Holocene simulations exhibit a 20% reduction of ENSO strength, caused by a precession forced enhancement of the Indian summer monsoon, which strengthened ENSO-related Bjerknes feedbacks. ENSO strength in the LGM is weakened by ~25%, which is not found to be caused by changes in equatorial Pacific dynamics but rather mean state cooling that weakens the tropical thermocline. The 2x and 4x simulations have strongly enhanced and more frequent ENSO events caused by disproportionate warming of the eastern Pacific relative to the western Pacific, which weakens the east-west Pacific surface temperature gradient, allowing larger anomalies, and hence ENSO events, to develop. Title: Simulating past, present, and future changes in ENSO : a model evaluation and data-model comparison Author: Alder, Jay R. This thesis presents the results of a formal evaluation of a new AOGCM, GENMOM, demonstrating its ability to simulate present-day climate and ENSO dynamics. The model is applied to simulate climate for the Last Glacial Maximum, deglacial, and Holocene time periods. The model output is evaluated against the best available proxy reconstructions in a detailed data-model comparison. ENSO strength is analyzed in seven paleo simulations and compared to coral and laminated lake sediment proxy records to provide an understanding of how ENSO related mechanisms varied in the past and how they vary under increased atmospheric CO₂ forced global warming. The GENMOM simulated present-day is found to be on par with three models used in the IPCC AR4 assessment and is comparable with reanalysis products (e.g, NCEP2). Atmospheric features such as the jet stream structure and major semipermanent sea level pressure centers are well simulated as is the mean planetary-scale wind structure that is needed to produce the correct position of stormtracks. Most ocean surface currents are reproduced except where they are not resolvable at T31 resolution. Overall, GENMOM captures the observed gradients and spatial distributions of annual surface temperature and precipitation and the simulations are on par with other AOGCMs. Deficiencies in the GENMOM present-day simulation include a warm bias in the surface temperature over the southern oceans, a split in the ITCZ and weaker-thanobserved overturning circulation. GENMOM produces a global temperature bias of 0.6 °C. GENMOM is demonstrated to capture ENSO dynamics similar to eight AOGCMs that were evaluated in the IPCC AR4. The Niño 3 - 4 indices have a standard deviation within 0.3 °C of the observations, indicating GENMOM is producing variability in the tropical Pacifc that is comparable to observations. GENMOM produces present-day ENSO events with an average period of 5.6 years, which is within the 2 – 7 range exhibited in the observed historical record. The mid-Holocene (6ka) and Last Glacial Maximum (LGM, 21ka) simulations are compared to the best available proxy reconstructions for sea surface temperature, precipitation and net moisture to ensure the simulations are plausible. This thesis finds that the model is in good agreement over broad spatial scales, with regional discrepancies between the model and proxy data. Coral and laminated lake sediment proxy records indicate mid-Holocene ENSO strength was reduced by 15 - 60%, offering a scenario in which ENSO-related components can be tested in climates different than present-day, thereby providing context for future changes in ENSO. The mid-Holocene simulations exhibit a 20% reduction of ENSO strength, caused by a precession forced enhancement of the Indian summer monsoon, which strengthened ENSO-related Bjerknes feedbacks. ENSO strength in the LGM is weakened by ~25%, which is not found to be caused by changes in equatorial Pacific dynamics but rather mean state cooling that weakens the tropical thermocline. The 2x and 4x simulations have strongly enhanced and more frequent ENSO events caused by disproportionate warming of the eastern Pacific relative to the western Pacific, which weakens the east-west Pacific surface temperature gradient, allowing larger anomalies, and hence ENSO events, to develop. Close

• 50. [Article] Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives

  This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Elsevier. The published article can be found at: http://www.journals.elsevier.com/quaternary-sc...

  Citation × Citation Citation Abstract Copy Title: Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives Author: Masson-Delmotte, V., Waelbroeck, C., Blunier, T., Capron, E., Tzedakis, P. C., Hillaire-Marcel, C., Seidenkrantz, M.-S., Zahn, R., Ghaleb, B., Veres, D., Bazin, L., Bassinot, F., Jimenez-Amat, P., Landais, A., Govin, A., St-Onge, G., Martrat, B., Parrenin, F., Genty, D., Verheyden, S., Stoner, J. S., Gersonde, R., Combourieu-Nebout, N., El Ouahabi, A. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Elsevier. The published article can be found at: http://www.journals.elsevier.com/quaternary-science-reviews/ Title: Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives Author: Masson-Delmotte, V., Waelbroeck, C., Blunier, T., Capron, E., Tzedakis, P. C., Hillaire-Marcel, C., Seidenkrantz, M.-S., Zahn, R., Ghaleb, B., Veres, D., Bazin, L., Bassinot, F., Jimenez-Amat, P., Landais, A., Govin, A., St-Onge, G., Martrat, B., Parrenin, F., Genty, D., Verheyden, S., Stoner, J. S., Gersonde, R., Combourieu-Nebout, N., El Ouahabi, A. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Elsevier. The published article can be found at: http://www.journals.elsevier.com/quaternary-science-reviews/ Close