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• 21. [Article] Distributed Modeling of Ablation (1996–2011) and Climate Sensitivity on the Glaciers of Taylor Valley, Antarctica

  The McMurdo Dry Valleys of Antarctica host the coldest and driest ecosystem on Earth, which is acutely sensitive to the availability of water coming from glacial runoff. We modeled the spatial variability ...

  Citation × Citation Citation Abstract Copy Title: Distributed Modeling of Ablation (1996–2011) and Climate Sensitivity on the Glaciers of Taylor Valley, Antarctica Author: Hoffman, Matthew J., Fountain, Andrew G., Liston, Glen E. Year: 2016 The McMurdo Dry Valleys of Antarctica host the coldest and driest ecosystem on Earth, which is acutely sensitive to the availability of water coming from glacial runoff. We modeled the spatial variability in ablation and assessed climate sensitivity of the glacier ablation zones using 16 years of meteorological and surface mass-balance observations collected in Taylor Valley. Sublimation was the primary form of mass loss over much of the ablation zones, except for near the termini where melt, primarily below the surface, dominated. Microclimates in ~10 m scale topographic basins generated melt rates up to ten times higher than over smooth glacier surfaces. In contrast, the vertical terminal cliffs on the glaciers can have higher or lower melt rates than the horizontal surfaces due to differences in incoming solar radiation. The model systematically underpredicted ablation for the final 5 years studied, possibly due to an increase of windblown sediment. Surface mass-balance sensitivity to temperature was ~−0.02 m w.e. K−1, which is among the smallest magnitudes observed globally. We also identified a high sensitivity to ice albedo, with a decrease of 0.02 having similar effects as a 1 K increase in temperature, and a complex sensitivity to wind speed. Title: Distributed Modeling of Ablation (1996–2011) and Climate Sensitivity on the Glaciers of Taylor Valley, Antarctica Author: Hoffman, Matthew J., Fountain, Andrew G., Liston, Glen E. Year: 2016 The McMurdo Dry Valleys of Antarctica host the coldest and driest ecosystem on Earth, which is acutely sensitive to the availability of water coming from glacial runoff. We modeled the spatial variability in ablation and assessed climate sensitivity of the glacier ablation zones using 16 years of meteorological and surface mass-balance observations collected in Taylor Valley. Sublimation was the primary form of mass loss over much of the ablation zones, except for near the termini where melt, primarily below the surface, dominated. Microclimates in ~10 m scale topographic basins generated melt rates up to ten times higher than over smooth glacier surfaces. In contrast, the vertical terminal cliffs on the glaciers can have higher or lower melt rates than the horizontal surfaces due to differences in incoming solar radiation. The model systematically underpredicted ablation for the final 5 years studied, possibly due to an increase of windblown sediment. Surface mass-balance sensitivity to temperature was ~−0.02 m w.e. K−1, which is among the smallest magnitudes observed globally. We also identified a high sensitivity to ice albedo, with a decrease of 0.02 having similar effects as a 1 K increase in temperature, and a complex sensitivity to wind speed. Close

• 22. [Article] A New Numerical Model of Coupled Inland Ice Sheet, Ice Stream, and Ice Shelf Flow and its Application to the West Antarctic Ice Sheet

  We have developed a dynamic/thermodynamic finite element numerical model that couples inland ice sheet, ice stream, and ice shelf dynamics. This new model stands apart from other whole ice sheet models ...

  Citation × Citation Citation Abstract Copy Title: A New Numerical Model of Coupled Inland Ice Sheet, Ice Stream, and Ice Shelf Flow and its Application to the West Antarctic Ice Sheet Author: Hulbe, Christina L., MacAyeal, D. R. Year: 1999 We have developed a dynamic/thermodynamic finite element numerical model that couples inland ice sheet, ice stream, and ice shelf dynamics. This new model stands apart from other whole ice sheet models in its explicit treatment of ice stream flow. Additionally, the model accounts for both horizontal and vertical advection and diffusion of temperature in the flowing ice. In present day simulations of the West Antarctic Ice Sheet (WAIS), modeled ice velocity agrees well with observed ice flow. In particular, the model reproduces the pattern of speed variation across ice streams although the continuous downstream speed up of ice flow cannot be reproduced without concurrent downstream variation in basal friction. Model thermodynamics, evaluated qualitatively by model prediction of the spatial distribution of basal melting and quantitatively by comparison with ice temperature measured in boreholes at several locations, are sound. In particular, the model reproduces the broad pattern of frozen-bed inter-ice stream ridges and melted-bed ice streams. Model initialization for long-time simulations is somewhat limited by computation time and by a thermodynamic feedback at sites of large viscous heating that can be a problem in heat balance only model initializations. Methods for averting those initialization problems are discussed. The new model can accommodate a variety of boundary conditions (such as various bed rheologies) and is well-suited to investigate the origin and evolution of WAIS ice streams within the context of the whole ice sheet system. Title: A New Numerical Model of Coupled Inland Ice Sheet, Ice Stream, and Ice Shelf Flow and its Application to the West Antarctic Ice Sheet Author: Hulbe, Christina L., MacAyeal, D. R. Year: 1999 We have developed a dynamic/thermodynamic finite element numerical model that couples inland ice sheet, ice stream, and ice shelf dynamics. This new model stands apart from other whole ice sheet models in its explicit treatment of ice stream flow. Additionally, the model accounts for both horizontal and vertical advection and diffusion of temperature in the flowing ice. In present day simulations of the West Antarctic Ice Sheet (WAIS), modeled ice velocity agrees well with observed ice flow. In particular, the model reproduces the pattern of speed variation across ice streams although the continuous downstream speed up of ice flow cannot be reproduced without concurrent downstream variation in basal friction. Model thermodynamics, evaluated qualitatively by model prediction of the spatial distribution of basal melting and quantitatively by comparison with ice temperature measured in boreholes at several locations, are sound. In particular, the model reproduces the broad pattern of frozen-bed inter-ice stream ridges and melted-bed ice streams. Model initialization for long-time simulations is somewhat limited by computation time and by a thermodynamic feedback at sites of large viscous heating that can be a problem in heat balance only model initializations. Methods for averting those initialization problems are discussed. The new model can accommodate a variety of boundary conditions (such as various bed rheologies) and is well-suited to investigate the origin and evolution of WAIS ice streams within the context of the whole ice sheet system. Close

• 23. [Article] The Differing Biogeochemical and Microbial Signatures of Glaciers and Rock Glaciers

  Glaciers and rock glaciers supply water and bioavailable nutrients to headwater mountain lakes and streams across all regions of the American West. Here we present a comparative study of the metal, nutrient, ...

  Citation × Citation Citation Abstract Copy Title: The Differing Biogeochemical and Microbial Signatures of Glaciers and Rock Glaciers Author: Fegel, Timothy S., Baron, Jill S., Fountain, Andrew G., Johnson, Gunnar F., Hall, Ed K. Year: 2016 Glaciers and rock glaciers supply water and bioavailable nutrients to headwater mountain lakes and streams across all regions of the American West. Here we present a comparative study of the metal, nutrient, and microbial characteristics of glacial and rock glacial influence on headwater ecosystems in three mountain ranges of the contiguous U.S.: the Cascade Mountains, Rocky Mountains, and Sierra Nevada. Several meltwater characteristics (water temperature, conductivity, pH, metals, nutrients, complexity of dissolved organic matter (DOM), and bacterial richness and diversity) differed significantly between glacier and rock glacier meltwaters, while other characteristics (Ca2+, Fe3+, SiO2 concentrations, reactive nitrogen, and microbial processing of DOM) showed distinct trends between mountain ranges regardless of meltwater source. Some characteristics were affected both by glacier type and mountain range (e.g., temperature, ammonium (NH4 +) and nitrate (NO3-) concentrations, and bacterial diversity). Due to the ubiquity of rock glaciers and the accelerating loss of the low-latitude glaciers, our results point to the important and changing influence that these frozen features place on headwater ecosystems. Title: The Differing Biogeochemical and Microbial Signatures of Glaciers and Rock Glaciers Author: Fegel, Timothy S., Baron, Jill S., Fountain, Andrew G., Johnson, Gunnar F., Hall, Ed K. Year: 2016 Glaciers and rock glaciers supply water and bioavailable nutrients to headwater mountain lakes and streams across all regions of the American West. Here we present a comparative study of the metal, nutrient, and microbial characteristics of glacial and rock glacial influence on headwater ecosystems in three mountain ranges of the contiguous U.S.: the Cascade Mountains, Rocky Mountains, and Sierra Nevada. Several meltwater characteristics (water temperature, conductivity, pH, metals, nutrients, complexity of dissolved organic matter (DOM), and bacterial richness and diversity) differed significantly between glacier and rock glacier meltwaters, while other characteristics (Ca2+, Fe3+, SiO2 concentrations, reactive nitrogen, and microbial processing of DOM) showed distinct trends between mountain ranges regardless of meltwater source. Some characteristics were affected both by glacier type and mountain range (e.g., temperature, ammonium (NH4 +) and nitrate (NO3-) concentrations, and bacterial diversity). Due to the ubiquity of rock glaciers and the accelerating loss of the low-latitude glaciers, our results point to the important and changing influence that these frozen features place on headwater ecosystems. Close

• 24. [Article] NWA 8614: The Least Heated Winonaite

  Northwest Africa 8614 is classified as a winonaite on the basis of oxygen isotope ratios, mineralogy, and highly reduced chemistry. Unlike other winonaites, it contains numerous and readily apparent chondrules. ...

  Citation × Citation Citation Abstract Copy Title: NWA 8614: The Least Heated Winonaite Author: Farley, Karla, Ruzicka, Alexander M., Armstrong, Katherine Year: 2015 Northwest Africa 8614 is classified as a winonaite on the basis of oxygen isotope ratios, mineralogy, and highly reduced chemistry. Unlike other winonaites, it contains numerous and readily apparent chondrules. Here we discuss various features of NWA 8614 and the possible significance of the meteorite. Petrological and chemical analyses were performed using optical microscopy with a DM2500 Leica petrographic microscope and a Zeiss Sigma VP-FEG scanning electron microscope (SEM) with a high-efficiency energy dispersive spectrometer (EDS). Oxygen isotopes were analyzed by Karen Ziegler at the University of New Mexico on acid-washed samples to remove terrestrial weathering products. Owing to the abundance of chondrules, NWA 8641 may be one of the least heated winonaites, and therefore may provide clues to the chondritic protolith of the winonaite parent body. Overall textures are similar to those found in type 6 chondrites that escaped significant melting. Despite similar geothermometer temperatures for various mineral pairs, NWA 8614 apparently did not attain Fe-Mg equilibrium between olivine and pyroxene. Like other winonaites, NWA 8614 has olivine compositions that are too magnesian for equilibrium relative to low-Ca pyroxene. Among winonaites as a whole, there is no evidence for a curved trend between Fa and Fs compositions as would be expected for FeO-reduction during metamorphism [Benedix, et al 1998], nor for mineral compositions that correlate with geothermometry temperatures. This argues against a single metamorphic FeO-reduction trend from a common chondritic precursor. Instead, protoliths for different winonaites may have varied slightly in composition. Title: NWA 8614: The Least Heated Winonaite Author: Farley, Karla, Ruzicka, Alexander M., Armstrong, Katherine Year: 2015 Northwest Africa 8614 is classified as a winonaite on the basis of oxygen isotope ratios, mineralogy, and highly reduced chemistry. Unlike other winonaites, it contains numerous and readily apparent chondrules. Here we discuss various features of NWA 8614 and the possible significance of the meteorite. Petrological and chemical analyses were performed using optical microscopy with a DM2500 Leica petrographic microscope and a Zeiss Sigma VP-FEG scanning electron microscope (SEM) with a high-efficiency energy dispersive spectrometer (EDS). Oxygen isotopes were analyzed by Karen Ziegler at the University of New Mexico on acid-washed samples to remove terrestrial weathering products. Owing to the abundance of chondrules, NWA 8641 may be one of the least heated winonaites, and therefore may provide clues to the chondritic protolith of the winonaite parent body. Overall textures are similar to those found in type 6 chondrites that escaped significant melting. Despite similar geothermometer temperatures for various mineral pairs, NWA 8614 apparently did not attain Fe-Mg equilibrium between olivine and pyroxene. Like other winonaites, NWA 8614 has olivine compositions that are too magnesian for equilibrium relative to low-Ca pyroxene. Among winonaites as a whole, there is no evidence for a curved trend between Fa and Fs compositions as would be expected for FeO-reduction during metamorphism [Benedix, et al 1998], nor for mineral compositions that correlate with geothermometry temperatures. This argues against a single metamorphic FeO-reduction trend from a common chondritic precursor. Instead, protoliths for different winonaites may have varied slightly in composition. Close

• 25. [Article] Quantification of the temperature, pressure and compositional dependence of trace element partitioning : an experimental and theoretical study

  The thermodynamic history of the Earth is preserved in the trace element record created through igneous processes. The ability to interpret that record depends on the accuracy and precision of numerical ...

  Citation × Citation Citation Abstract Copy Title: Quantification of the temperature, pressure and compositional dependence of trace element partitioning : an experimental and theoretical study Author: Cunningham, Jennifer Lynn The thermodynamic history of the Earth is preserved in the trace element record created through igneous processes. The ability to interpret that record depends on the accuracy and precision of numerical models that connect igneous processes with their geochemical consequences. This project answers three major questions concerning the relationship between trace element partitioning and the processes that influence it. One: using a common igneous mineral, clinopyroxene, as a base, how complete is the dataset on which our understanding of this relationship relies? Two: what are the dangers involved with basing models on experiments that contain higher than natural concentrations of trace elements? Three: how accurate and precise is the current numerical model that describes this relationship, and can it be improved? This project determined that the data contain gaps at high pressures and temperatures, are limited for felsic rock compositions, and are lacking for hydrous conditions. A set of experiments conducted on plagioclase feldspar crystallization from a base MORB composition containing various levels of dopants at below wt% levels reveals the presence of non-Henry's Law partitioning behavior through the disruption of the phase equilibria of the system. Lastly, the current clinopyroxene/melt rare earth element partitioning model (Wood and Blundy, 2003) is shown to reasonably, though less than ideally, describe the relationship between igneous processes and their trace-element partitioning results using the thermodynamics of the system. The accuracy was improved through adding a regression, which is based on the major element concentrations of the clinopyroxene and melt to the original numerical expressions. Title: Quantification of the temperature, pressure and compositional dependence of trace element partitioning : an experimental and theoretical study Author: Cunningham, Jennifer Lynn The thermodynamic history of the Earth is preserved in the trace element record created through igneous processes. The ability to interpret that record depends on the accuracy and precision of numerical models that connect igneous processes with their geochemical consequences. This project answers three major questions concerning the relationship between trace element partitioning and the processes that influence it. One: using a common igneous mineral, clinopyroxene, as a base, how complete is the dataset on which our understanding of this relationship relies? Two: what are the dangers involved with basing models on experiments that contain higher than natural concentrations of trace elements? Three: how accurate and precise is the current numerical model that describes this relationship, and can it be improved? This project determined that the data contain gaps at high pressures and temperatures, are limited for felsic rock compositions, and are lacking for hydrous conditions. A set of experiments conducted on plagioclase feldspar crystallization from a base MORB composition containing various levels of dopants at below wt% levels reveals the presence of non-Henry's Law partitioning behavior through the disruption of the phase equilibria of the system. Lastly, the current clinopyroxene/melt rare earth element partitioning model (Wood and Blundy, 2003) is shown to reasonably, though less than ideally, describe the relationship between igneous processes and their trace-element partitioning results using the thermodynamics of the system. The accuracy was improved through adding a regression, which is based on the major element concentrations of the clinopyroxene and melt to the original numerical expressions. Close

• 26. [Article] Quantifying 20th Century Glacier Change in the Sierra Nevada, California

  Numerous small alpine glaciers occupy the high elevation regions of the central and southern Sierra Nevada, California. An inventory based on 1:24,000 topographic maps revealed 1719 glaciers and perennial ...

  Citation × Citation Citation Abstract Copy Title: Quantifying 20th Century Glacier Change in the Sierra Nevada, California Author: Fountain, Andrew G., Basagic, Hassan J. Year: 2011 Numerous small alpine glaciers occupy the high elevation regions of the central and southern Sierra Nevada, California. An inventory based on 1:24,000 topographic maps revealed 1719 glaciers and perennial snowfields for a total area of 39.15 +/- 0.13 km(2). The number of 'true' glaciers, versus non-moving ice, is estimated to be 122 covering 14.89 +/- 0.08 km(2) or 38% of the ice-covered area. Historic photographs, geologic evidence, and field mapping were used to determine the magnitude of area change over the past century at 14 glaciers. The area change between 1903 and 2004 ranged from -31% to -78%, averaging -55%. Based on these values rough estimates of volume change suggest an ice volume loss from 1903 (1.09 km(3)) to 2004 (0.43 km(3)) of 0.66 km(3) (0.59 km(3) water). Rapid retreat occurred over the first half of the 20th century beginning in the 1920s and continued through the 1960s after which recession ceased by the early 1980s and some glaciers advanced. Since the late 1980s glaciers resumed retreat with a rapid acceleration starting in the early 2000s. The relatively uniform timing of area changes in the study glaciers is a response to regional climate whereas the magnitude of change is influenced by local topographic effects. Area changes correlate significantly with changes in summer and winter air temperatures. Warmer winter temperatures warm the snowpack lengthening the summer melt season. Spring air temperatures and precipitation may also play an important role. The occurrence of spring snowfall can delay the onset of melt due to the increased surface albedo. Examining the influence of topographic variables we only found headwall height at the top of the glacier to show an influence on glacier change. Higher headwalls shadow the glacier from solar radiation reducing melt and enhancing snow accumulation via avalanching. If the glaciers continue to shrink at current (1972-2004) rates, most will disappear in 50-250 years. Title: Quantifying 20th Century Glacier Change in the Sierra Nevada, California Author: Fountain, Andrew G., Basagic, Hassan J. Year: 2011 Numerous small alpine glaciers occupy the high elevation regions of the central and southern Sierra Nevada, California. An inventory based on 1:24,000 topographic maps revealed 1719 glaciers and perennial snowfields for a total area of 39.15 +/- 0.13 km(2). The number of 'true' glaciers, versus non-moving ice, is estimated to be 122 covering 14.89 +/- 0.08 km(2) or 38% of the ice-covered area. Historic photographs, geologic evidence, and field mapping were used to determine the magnitude of area change over the past century at 14 glaciers. The area change between 1903 and 2004 ranged from -31% to -78%, averaging -55%. Based on these values rough estimates of volume change suggest an ice volume loss from 1903 (1.09 km(3)) to 2004 (0.43 km(3)) of 0.66 km(3) (0.59 km(3) water). Rapid retreat occurred over the first half of the 20th century beginning in the 1920s and continued through the 1960s after which recession ceased by the early 1980s and some glaciers advanced. Since the late 1980s glaciers resumed retreat with a rapid acceleration starting in the early 2000s. The relatively uniform timing of area changes in the study glaciers is a response to regional climate whereas the magnitude of change is influenced by local topographic effects. Area changes correlate significantly with changes in summer and winter air temperatures. Warmer winter temperatures warm the snowpack lengthening the summer melt season. Spring air temperatures and precipitation may also play an important role. The occurrence of spring snowfall can delay the onset of melt due to the increased surface albedo. Examining the influence of topographic variables we only found headwall height at the top of the glacier to show an influence on glacier change. Higher headwalls shadow the glacier from solar radiation reducing melt and enhancing snow accumulation via avalanching. If the glaciers continue to shrink at current (1972-2004) rates, most will disappear in 50-250 years. Close

• 27. [Article] Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust

  xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.

  Citation × Citation Citation Abstract Copy Title: Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust Author: Mercer, Celestine Nicole, 1979- Year: 2010, 2009 xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. Title: Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust Author: Mercer, Celestine Nicole, 1979- Year: 2010, 2009 xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. Close

• 28. [Article] Biostratigraphy of the Type Yamhill Formation, Polk County, Oregon

  One hundred and seventy-four species and varieties of fossil Foraminifera are recorded from thirty-eight localities in the Siletz River Volcanics, Yamhill and Nestucca Formations exposed along Mill and ...

  Citation × Citation Citation Abstract Copy Title: Biostratigraphy of the Type Yamhill Formation, Polk County, Oregon Author: Gaston, Larry R. Year: 1974 One hundred and seventy-four species and varieties of fossil Foraminifera are recorded from thirty-eight localities in the Siletz River Volcanics, Yamhill and Nestucca Formations exposed along Mill and Gooseneck Creeks, in the Northern Coast Range of Oregon. Marginulina holmesi is described as new. The Foraminifera indicate that this sequence was deposited during late Ulatisian and Narizian time, in marine waters at bathyal or lower neritic depths, with cool surface temperatures. The Yamhill Formation can be correlated with Moody Shale member of the Toledo Formation and the Coaledo Formation of Oregon; the McIntosh and Aldwell Formations of Washington; and the upper part of the Canoas siltstone member of the Kreyenhagen Formation and the Alhambra Formation of California. It is proposed to modify, in part, the type section of the Yamhill Formation. Approximately 2.2 miles of the section, south of the Yamhill River Fault, are excluded from the original type area. Biostratigraphic studies of foraminiferal faunae from adjacent sides of the Yamhill River Fault suggest only minor vertical displacement. Title: Biostratigraphy of the Type Yamhill Formation, Polk County, Oregon Author: Gaston, Larry R. Year: 1974 One hundred and seventy-four species and varieties of fossil Foraminifera are recorded from thirty-eight localities in the Siletz River Volcanics, Yamhill and Nestucca Formations exposed along Mill and Gooseneck Creeks, in the Northern Coast Range of Oregon. Marginulina holmesi is described as new. The Foraminifera indicate that this sequence was deposited during late Ulatisian and Narizian time, in marine waters at bathyal or lower neritic depths, with cool surface temperatures. The Yamhill Formation can be correlated with Moody Shale member of the Toledo Formation and the Coaledo Formation of Oregon; the McIntosh and Aldwell Formations of Washington; and the upper part of the Canoas siltstone member of the Kreyenhagen Formation and the Alhambra Formation of California. It is proposed to modify, in part, the type section of the Yamhill Formation. Approximately 2.2 miles of the section, south of the Yamhill River Fault, are excluded from the original type area. Biostratigraphic studies of foraminiferal faunae from adjacent sides of the Yamhill River Fault suggest only minor vertical displacement. Close

• 29. [Article] The Impact of a Large-Scale Climate Event on Antarctic Ecosystem Processes

  Extreme climate and weather events, such as a drought, hurricanes, or ice storms, can strongly imprint ecosystem processing and may alter ecosystem structure. Ecosystems in extreme environments are particularly ...

  Citation × Citation Citation Abstract Copy Title: The Impact of a Large-Scale Climate Event on Antarctic Ecosystem Processes Author: Fountain, Andrew G., Saba, Grace, Adams, Byron, Doran, Peter, Fraser, William, Gooseff, Michael N., Obryk, Maciej K., Priscu, John Charles, Stammerjohn, Sharon, Virginia, Ross A. Year: 2016 Extreme climate and weather events, such as a drought, hurricanes, or ice storms, can strongly imprint ecosystem processing and may alter ecosystem structure. Ecosystems in extreme environments are particularly vulnerable because of their adaptation to severe limitations in energy, water, or nutrients. The vulnerability can be expressed as a relatively long-lasting ecosystem response to a small or brief change in environmental conditions. Such an event occurred in Antarctica and affected two vastly different ecosystems: a marine-dominated coastal system and a terrestrial polar desert. Both sites experienced winds that warmed air temperatures above the 0°C threshold, resulting in extensive snow and ice melt and triggering a series of cascading effects through the ecosystems that are continuing to play out more than a decade later. This highlights the sensitivity of Antarctic ecosystems to warming events, which should occur more frequently in the future with global climate warming. Title: The Impact of a Large-Scale Climate Event on Antarctic Ecosystem Processes Author: Fountain, Andrew G., Saba, Grace, Adams, Byron, Doran, Peter, Fraser, William, Gooseff, Michael N., Obryk, Maciej K., Priscu, John Charles, Stammerjohn, Sharon, Virginia, Ross A. Year: 2016 Extreme climate and weather events, such as a drought, hurricanes, or ice storms, can strongly imprint ecosystem processing and may alter ecosystem structure. Ecosystems in extreme environments are particularly vulnerable because of their adaptation to severe limitations in energy, water, or nutrients. The vulnerability can be expressed as a relatively long-lasting ecosystem response to a small or brief change in environmental conditions. Such an event occurred in Antarctica and affected two vastly different ecosystems: a marine-dominated coastal system and a terrestrial polar desert. Both sites experienced winds that warmed air temperatures above the 0°C threshold, resulting in extensive snow and ice melt and triggering a series of cascading effects through the ecosystems that are continuing to play out more than a decade later. This highlights the sensitivity of Antarctic ecosystems to warming events, which should occur more frequently in the future with global climate warming. Close

• 30. [Article] Mineral Evidence for Generating Compositionally Zoned Rhyolites of the Devine Canyon Tuff, High Lava Plains, Oregon

  Large-volume silicic eruptions are often evacuated from magma reservoirs which display gradients in composition, temperature, crystallinity, and volatile content. The 9.7 Ma Devine Canyon Tuff (DCT) of ...

  Citation × Citation Citation Abstract Copy Title: Mineral Evidence for Generating Compositionally Zoned Rhyolites of the Devine Canyon Tuff, High Lava Plains, Oregon Author: Shafer, Erik Paul Year: 2017 Large-volume silicic eruptions are often evacuated from magma reservoirs which display gradients in composition, temperature, crystallinity, and volatile content. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon represents such an eruption, with >300 km3 of compositionally zoned pyroclastic material deposited as a variably-welded ignimbrite. The ignimbrite displays homogenous bulk tuff major element compositions with a wide range of trace element compositions, allowing for the investigation of how these magmas were generated, stored, and modified in the magma reservoir by studying pumices which represent the primary magmas composing the DCT. Five pumices ranging from dacite to rhyolite bulk compositions were selected across the range of trace element compositions and were crushed and sieved to measure how crystallinity and mineral abundances change within each pumice at different particle size fractions. Single alkali feldspar and clinopyroxene crystals were analyzed using EMP and LA ICP-MS from each pumice. Physical results yielded a systematic decrease in crystallinity from 22% to 3% going from the dacite to the most evolved rhyolite composition, with the highest crystallinity occurring between Title: Mineral Evidence for Generating Compositionally Zoned Rhyolites of the Devine Canyon Tuff, High Lava Plains, Oregon Author: Shafer, Erik Paul Year: 2017 Large-volume silicic eruptions are often evacuated from magma reservoirs which display gradients in composition, temperature, crystallinity, and volatile content. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon represents such an eruption, with >300 km3 of compositionally zoned pyroclastic material deposited as a variably-welded ignimbrite. The ignimbrite displays homogenous bulk tuff major element compositions with a wide range of trace element compositions, allowing for the investigation of how these magmas were generated, stored, and modified in the magma reservoir by studying pumices which represent the primary magmas composing the DCT. Five pumices ranging from dacite to rhyolite bulk compositions were selected across the range of trace element compositions and were crushed and sieved to measure how crystallinity and mineral abundances change within each pumice at different particle size fractions. Single alkali feldspar and clinopyroxene crystals were analyzed using EMP and LA ICP-MS from each pumice. Physical results yielded a systematic decrease in crystallinity from 22% to 3% going from the dacite to the most evolved rhyolite composition, with the highest crystallinity occurring between Close