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• 41. [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

• 42. [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

• 43. [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

• 44. [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

• 45. [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

• 46. [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

• 47. [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

• 48. [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

• 49. [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

• 50. [Article] Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard-Oeschger oscillations caused by variations of North Atlantic Deep Water subduction

  Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature ...

  Citation × Citation Citation Abstract Copy Title: Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard-Oeschger oscillations caused by variations of North Atlantic Deep Water subduction Author: Hostetler, Steven W., Pedersen, Thomas F., Schmittner, Andreas, Galbraith, Eric D., Zhang, Rong Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature oscillations. Yet the mechanism of this teleconnection between the remote ocean basins remains elusive. Here we present model simulations of the oxygen and nitrogen cycles that explain how changes in deepwater subduction in the North Atlantic can cause large and synchronous variations of oxygen minimum zones throughout the Northern Hemisphere of the Indian and Pacific oceans, consistent with the paleoclimate records. Cold periods in the North Atlantic are associated with reduced nutrient delivery to the upper Indo-Pacific oceans, thereby decreasing productivity. Reduced export production diminishes subsurface respiration of organic matter leading to higher oxygen concentrations and less denitrification. This effect of reduced oxygen consumption dominates at low latitudes. At high latitudes in the Southern Ocean and North Pacific, increased mixed layer depths and steepening of isopycnals improve ocean ventilation and oxygen supply to the subsurface. Atmospheric teleconnections through changes in wind-driven ocean circulation modify this basin-scale pattern regionally. These results suggest that changes in the Atlantic Ocean circulation, similar to those projected by climate models to possibly occur in the centuries to come because of anthropogenic climate warming, can have large effects on marine ecosystems and biogeochemical cycles even in remote areas. Title: Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard-Oeschger oscillations caused by variations of North Atlantic Deep Water subduction Author: Hostetler, Steven W., Pedersen, Thomas F., Schmittner, Andreas, Galbraith, Eric D., Zhang, Rong Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature oscillations. Yet the mechanism of this teleconnection between the remote ocean basins remains elusive. Here we present model simulations of the oxygen and nitrogen cycles that explain how changes in deepwater subduction in the North Atlantic can cause large and synchronous variations of oxygen minimum zones throughout the Northern Hemisphere of the Indian and Pacific oceans, consistent with the paleoclimate records. Cold periods in the North Atlantic are associated with reduced nutrient delivery to the upper Indo-Pacific oceans, thereby decreasing productivity. Reduced export production diminishes subsurface respiration of organic matter leading to higher oxygen concentrations and less denitrification. This effect of reduced oxygen consumption dominates at low latitudes. At high latitudes in the Southern Ocean and North Pacific, increased mixed layer depths and steepening of isopycnals improve ocean ventilation and oxygen supply to the subsurface. Atmospheric teleconnections through changes in wind-driven ocean circulation modify this basin-scale pattern regionally. These results suggest that changes in the Atlantic Ocean circulation, similar to those projected by climate models to possibly occur in the centuries to come because of anthropogenic climate warming, can have large effects on marine ecosystems and biogeochemical cycles even in remote areas. Close