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• 31. [Article] The Changing Extent of the Glaciers Along the Western Ross Sea, Antarctica

  We examine the change in terminus positions of glaciers flowing into the western Ross Sea, Antarctica, between 71°S and 78°S as a proxy for changes in snowfall and/or summer air temperature. This coastline's ...

  Citation × Citation Citation Abstract Copy Title: The Changing Extent of the Glaciers Along the Western Ross Sea, Antarctica Author: Fountain, Andrew G., Glenn, Bryce, Scambos, Ted A. Year: 2017 We examine the change in terminus positions of glaciers flowing into the western Ross Sea, Antarctica, between 71°S and 78°S as a proxy for changes in snowfall and/or summer air temperature. This coastline's major glaciers terminate in ice tongues, which are particularly sensitive to changes in flow rate and calving. Using historic maps and satellite imagery spanning 60 yr (A.D. 1955-2015), the terminus positions, ice speed, calving rates, and ice front advance and retreat rates for 34 glaciers are documented. Additionally, changes in regional ice flow speed from 2008 to 2014 are examined. No significant spatial or temporal patterns of terminus position, flow speed, or calving emerged, implying that the conditions associated with ice tongue stability are unchanged. A weak trend of advance may be present in the northernmost part of the coast, consistent with estimates of increased snow accumulation and glacier mass balance in that region. The stability of these glaciers over the past half century contrasts sharply with the rapidly shrinking glaciers of the Antarctic Peninsula and suggests that no significant climate change, as manifest in glacier change, has reached this region of Antarctica. The changing extent of the glaciers along the western Ross Sea, Antarctica. Title: The Changing Extent of the Glaciers Along the Western Ross Sea, Antarctica Author: Fountain, Andrew G., Glenn, Bryce, Scambos, Ted A. Year: 2017 We examine the change in terminus positions of glaciers flowing into the western Ross Sea, Antarctica, between 71°S and 78°S as a proxy for changes in snowfall and/or summer air temperature. This coastline's major glaciers terminate in ice tongues, which are particularly sensitive to changes in flow rate and calving. Using historic maps and satellite imagery spanning 60 yr (A.D. 1955-2015), the terminus positions, ice speed, calving rates, and ice front advance and retreat rates for 34 glaciers are documented. Additionally, changes in regional ice flow speed from 2008 to 2014 are examined. No significant spatial or temporal patterns of terminus position, flow speed, or calving emerged, implying that the conditions associated with ice tongue stability are unchanged. A weak trend of advance may be present in the northernmost part of the coast, consistent with estimates of increased snow accumulation and glacier mass balance in that region. The stability of these glaciers over the past half century contrasts sharply with the rapidly shrinking glaciers of the Antarctic Peninsula and suggests that no significant climate change, as manifest in glacier change, has reached this region of Antarctica. The changing extent of the glaciers along the western Ross Sea, Antarctica. Close

• 32. [Article] An ice-shelf model test based on the Ross ice shelf

  A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution ...

  Citation × Citation Citation Abstract Copy Title: An ice-shelf model test based on the Ross ice shelf Author: MacAyeal, D. R., Rommelaere, V., Huybrechts, P., Hulbe, Christina L., Determann, J., Ritz, C. Year: 1996 A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution of stress-equilibrium equations for an ice-shelf velocity consistent with present observations. As a demonstration, we compare five independently developed ice-shelf models based on finite-difference and finite-element methods. Our results suggest that there is little difference between finite-element and finite-difference methods in capturing the basic, large-scale flow features of the ice shelf. We additionally show that the fit between model and observed velocity depends strongly on the ice-shelf temperature field for which there is presently little observational control. The main differences between model results are due to the equations being solved, the boundary conditions at the ice front and the discretization method (finite element vs. finite difference) Title: An ice-shelf model test based on the Ross ice shelf Author: MacAyeal, D. R., Rommelaere, V., Huybrechts, P., Hulbe, Christina L., Determann, J., Ritz, C. Year: 1996 A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution of stress-equilibrium equations for an ice-shelf velocity consistent with present observations. As a demonstration, we compare five independently developed ice-shelf models based on finite-difference and finite-element methods. Our results suggest that there is little difference between finite-element and finite-difference methods in capturing the basic, large-scale flow features of the ice shelf. We additionally show that the fit between model and observed velocity depends strongly on the ice-shelf temperature field for which there is presently little observational control. The main differences between model results are due to the equations being solved, the boundary conditions at the ice front and the discretization method (finite element vs. finite difference) Close

• 33. [Article] Analysis and numerical simulation of the ground water system at the Bonneville navigation lock site, Oregon

  As part of the new navigation lock for Bonneville Dam a new water source for the Bonneville Fish Hatchery must be supplied. The hatchery is located on the Oregon side of the Columbia River downstream of ...

  Citation × Citation Citation Abstract Copy Title: Analysis and numerical simulation of the ground water system at the Bonneville navigation lock site, Oregon Author: Baron, Dirk Year: 1990 As part of the new navigation lock for Bonneville Dam a new water source for the Bonneville Fish Hatchery must be supplied. The hatchery is located on the Oregon side of the Columbia River downstream of the dam. It requires large quantities of water free from chemical and biological contamination. In addition, the water has to be in a narrow temperature range. Currently the fish hatchery receives its water from a well field that is located on the alluvial terrace downstream of Bonneville Dam. The well field lies in the proposed approach channel for the new lock and has to be abandoned during construction of the lock. For the continued water supply of the hatchery, a new well field will be developed north of the approach channel. Early in the planning phase for the new lock, concerns were raised about the potential impact of the relocation of the well field and the excavation of the new approach channel on the hatchery. To assess these concerns and to assure a continuous water supply during and after construction, a hydrogeologic investigation was initiated. Within the framework of the investigation this study focuses on the analysis of pumping test data and the development of a three-dimensional ground water flow model for the site. Title: Analysis and numerical simulation of the ground water system at the Bonneville navigation lock site, Oregon Author: Baron, Dirk Year: 1990 As part of the new navigation lock for Bonneville Dam a new water source for the Bonneville Fish Hatchery must be supplied. The hatchery is located on the Oregon side of the Columbia River downstream of the dam. It requires large quantities of water free from chemical and biological contamination. In addition, the water has to be in a narrow temperature range. Currently the fish hatchery receives its water from a well field that is located on the alluvial terrace downstream of Bonneville Dam. The well field lies in the proposed approach channel for the new lock and has to be abandoned during construction of the lock. For the continued water supply of the hatchery, a new well field will be developed north of the approach channel. Early in the planning phase for the new lock, concerns were raised about the potential impact of the relocation of the well field and the excavation of the new approach channel on the hatchery. To assess these concerns and to assure a continuous water supply during and after construction, a hydrogeologic investigation was initiated. Within the framework of the investigation this study focuses on the analysis of pumping test data and the development of a three-dimensional ground water flow model for the site. Close

• 34. [Article] Deformation and Thermal Histories of Ordinary Chondrites: Evidence for Postdeformation Annealing and Syn-Metamorphic Shock

  We show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post-deformation ...

  Citation × Citation Citation Abstract Copy Title: Deformation and Thermal Histories of Ordinary Chondrites: Evidence for Postdeformation Annealing and Syn-Metamorphic Shock Author: Ruzicka, Alexander M., Hugo, Richard, Hutson, Melinda Year: 2015 We show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post-deformation cooling setting of the meteorites, and to discriminate between collisions affecting cold and warm parent bodies. The L6 chondrites Park (shock stage S1), Bruderheim (S4), Leedey (S4), and Morrow County (S5) were affected by variable shock deformation followed by relatively rapid cooling, and probably cooled as fragments liberated by impact in near-surface settings. In contrast, Kernouvé (H6 S1), Portales Valley (H6/7 S1), and MIL 99301 (LL6 S1) appear to have cooled slowly after shock, probably by deep burial in warm materials. In these chondrites, post-deformation annealing lowered apparent optical strain levels in olivine. Additionally, Kernouvé, Morrow County, Park, MIL 99301, and possibly Portales Valley, show evidence for having been deformed at an elevated temperature (⩾800–1000 °C). The high temperatures for Morrow County can be explained by dynamic heating during intense shock, but Kernouvé, Park, and MIL 99301 were probably shocked while the H, L and LL parent bodies were warm, during early, endogenically-driven thermal metamorphism. Thus, whereas the S4 and S5 chondrites experienced purely shock-induced heating and cooling, all the S1 chondrites examined show evidence for static heating consistent with either syn-metamorphic shock (Kernouvé, MIL 99301, Park), post-deformation burial in warm materials (Kernouvé, MIL 99301, Portales Valley), or both. The results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies. Moreover, they provide support for the idea that “secondary” metamorphic and “tertiary” shock processes overlapped in time shortly after the accretion of chondritic planetesimals, and that impacts into warm asteroidal bodies were common. Title: Deformation and Thermal Histories of Ordinary Chondrites: Evidence for Postdeformation Annealing and Syn-Metamorphic Shock Author: Ruzicka, Alexander M., Hugo, Richard, Hutson, Melinda Year: 2015 We show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post-deformation cooling setting of the meteorites, and to discriminate between collisions affecting cold and warm parent bodies. The L6 chondrites Park (shock stage S1), Bruderheim (S4), Leedey (S4), and Morrow County (S5) were affected by variable shock deformation followed by relatively rapid cooling, and probably cooled as fragments liberated by impact in near-surface settings. In contrast, Kernouvé (H6 S1), Portales Valley (H6/7 S1), and MIL 99301 (LL6 S1) appear to have cooled slowly after shock, probably by deep burial in warm materials. In these chondrites, post-deformation annealing lowered apparent optical strain levels in olivine. Additionally, Kernouvé, Morrow County, Park, MIL 99301, and possibly Portales Valley, show evidence for having been deformed at an elevated temperature (⩾800–1000 °C). The high temperatures for Morrow County can be explained by dynamic heating during intense shock, but Kernouvé, Park, and MIL 99301 were probably shocked while the H, L and LL parent bodies were warm, during early, endogenically-driven thermal metamorphism. Thus, whereas the S4 and S5 chondrites experienced purely shock-induced heating and cooling, all the S1 chondrites examined show evidence for static heating consistent with either syn-metamorphic shock (Kernouvé, MIL 99301, Park), post-deformation burial in warm materials (Kernouvé, MIL 99301, Portales Valley), or both. The results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies. Moreover, they provide support for the idea that “secondary” metamorphic and “tertiary” shock processes overlapped in time shortly after the accretion of chondritic planetesimals, and that impacts into warm asteroidal bodies were common. Close

• 35. [Image] Geothermal Resources, Vicksburg Formation, Texas Gulf Coast

  	The potential for discovering geopressured geothermal reservoirs in the Vicksburg Formation is limited to Hidalgo County along the Lower Texas Gulf Coast. In Hidalgo County, an area of approximately 385 ...
  	Citation × Citation Citation Abstract Copy Title: Geothermal Resources, Vicksburg Formation, Texas Gulf Coast Author: Loucks, R.G. Year: 1978 The potential for discovering geopressured geothermal reservoirs in the Vicksburg Formation is limited to Hidalgo County along the Lower Texas Gulf Coast. In Hidalgo County, an area of approximately 385 square miles (designated the Vicksburg Fairway) contains up to 1,300 feet of geopressured sandstones with fluid temperatures greater than 300/sup 0/F. In-place effective permeability, however, averages less than 1 millidarcy in the Vicksburg sandstones because of fine grain size and extensive late carbonate cementation. Also, areal extent of individual reservoirs is limited in a dip direction by growth faults and in a strike direction by the lenticular morphology of the sandstone bodies. In conclusion, under the present specifications set for a geothermal fairway, the Vicksburg has minimal potential because of low reservoir deliverability, which is constrained by low permeability and somewhat limited reservoir continuity. If future tests indicate that lower permeabilities are acceptable, the Vicksburg Fairway should be reconsidered because of the presence of extremely thick sandstone bodies Title: Geothermal Resources, Vicksburg Formation, Texas Gulf Coast Author: Loucks, R.G. Year: 1978 The potential for discovering geopressured geothermal reservoirs in the Vicksburg Formation is limited to Hidalgo County along the Lower Texas Gulf Coast. In Hidalgo County, an area of approximately 385 square miles (designated the Vicksburg Fairway) contains up to 1,300 feet of geopressured sandstones with fluid temperatures greater than 300/sup 0/F. In-place effective permeability, however, averages less than 1 millidarcy in the Vicksburg sandstones because of fine grain size and extensive late carbonate cementation. Also, areal extent of individual reservoirs is limited in a dip direction by growth faults and in a strike direction by the lenticular morphology of the sandstone bodies. In conclusion, under the present specifications set for a geothermal fairway, the Vicksburg has minimal potential because of low reservoir deliverability, which is constrained by low permeability and somewhat limited reservoir continuity. If future tests indicate that lower permeabilities are acceptable, the Vicksburg Fairway should be reconsidered because of the presence of extremely thick sandstone bodies Close

• 36. [Article] Complex Thermal Histories of L Melt Breccias NWA 5964 and NWA 6580

  To constrain the thermal histories of two complex L chondrite melt breccia samples (NWA 5964 and NWA 6580) we compare textures and chemical compositions of metal and sulfide to L melt rock (NWA 6454 and ...

  Citation × Citation Citation Abstract Copy Title: Complex Thermal Histories of L Melt Breccias NWA 5964 and NWA 6580 Author: Schepker, Kristy Lee Year: 2014 To constrain the thermal histories of two complex L chondrite melt breccia samples (NWA 5964 and NWA 6580) we compare textures and chemical compositions of metal and sulfide to L melt rock (NWA 6454 and NWA 6579) and strongly shocked (shock stage S6) (NWA 4860) samples. The inferred thermal histories can be used to evaluate formation settings on the L chondrite parent body. The L melt samples probably formed as different melt units within warm but largely unmelted material relatively close to the surface of the parent body, and the same is true for the S6 sample, except it experienced less melting. The breccia samples likely formed deeper, below different impact craters, by the injection of shock melt into a cooler chondritic basement. Carbide grains in the melt breccias could have formed by a contact metamorphic process caused by heating of the chondritic basement in proximity to the melt. Within the melt regions of the various samples, inferred cooling rates are on the order of 1-10 °C/sec, whereas in the chondritic portions of the melt breccias, the inferred cooling rates are many orders of magnitude slower, ~1-100 °C/My. The complex intergrowths of metal and FeS (hereafter referred to as dendritic grains) within the melt are recording cooling rates above the metal-sulfide eutectic, while the metal grains outside of the melt regions are recording cooling rates at much lower temperatures. It is likely the melt regions in the breccias cooled substantially prior to coming to rest against the chondritic basement, and thereafter the melt-chondrite rocks cooled more slowly. Title: Complex Thermal Histories of L Melt Breccias NWA 5964 and NWA 6580 Author: Schepker, Kristy Lee Year: 2014 To constrain the thermal histories of two complex L chondrite melt breccia samples (NWA 5964 and NWA 6580) we compare textures and chemical compositions of metal and sulfide to L melt rock (NWA 6454 and NWA 6579) and strongly shocked (shock stage S6) (NWA 4860) samples. The inferred thermal histories can be used to evaluate formation settings on the L chondrite parent body. The L melt samples probably formed as different melt units within warm but largely unmelted material relatively close to the surface of the parent body, and the same is true for the S6 sample, except it experienced less melting. The breccia samples likely formed deeper, below different impact craters, by the injection of shock melt into a cooler chondritic basement. Carbide grains in the melt breccias could have formed by a contact metamorphic process caused by heating of the chondritic basement in proximity to the melt. Within the melt regions of the various samples, inferred cooling rates are on the order of 1-10 °C/sec, whereas in the chondritic portions of the melt breccias, the inferred cooling rates are many orders of magnitude slower, ~1-100 °C/My. The complex intergrowths of metal and FeS (hereafter referred to as dendritic grains) within the melt are recording cooling rates above the metal-sulfide eutectic, while the metal grains outside of the melt regions are recording cooling rates at much lower temperatures. It is likely the melt regions in the breccias cooled substantially prior to coming to rest against the chondritic basement, and thereafter the melt-chondrite rocks cooled more slowly. Close

• 37. [Article] The Influence of Föhn Winds on Glacial Lake Washburn and Palaeotemperatures in the McMurdo Dry Valleys, Antarctica, During the Last Glacial Maximum

  Large glacial lakes, including Glacial Lake Washburn, were present in the McMurdo Dry Valleys, Antarctica, during the Last Glacial Maximum (LGM) despite a colder and drier climate. To address the mechanism ...

  Citation × Citation Citation Abstract Copy Title: The Influence of Föhn Winds on Glacial Lake Washburn and Palaeotemperatures in the McMurdo Dry Valleys, Antarctica, During the Last Glacial Maximum Author: Obryk, Maciej, Doran, Peter, Waddington, Ed, McKay, Chris Year: 2017 Large glacial lakes, including Glacial Lake Washburn, were present in the McMurdo Dry Valleys, Antarctica, during the Last Glacial Maximum (LGM) despite a colder and drier climate. To address the mechanism capable of generating enough meltwater to sustain these large lakes, a conceptual model was developed based on the warming potential of infrequent contemporary föhn winds. The model suggests that föhn winds were capable of generating enough meltwater to sustain large glacial lakes during the LGM by increasing degree days above freezing (DDAF) and prolonging the melt season. A present-day relationship between infrequent summer föhn winds and DDAF was established. It is assumed that the Taylor Dome ice core record represents large-scale palaeoclimatic variations for the McMurdo Dry Valleys region. This analysis suggests that because of the warming influence of the more frequent föhn winds, summer DDAF in the McMurdo Dry Valleys during the LGM were equivalent to present-day values, but this enhanced summer signal is not preserved in the annually averaged ice core temperature record. © Antarctic Science Ltd 2017 Title: The Influence of Föhn Winds on Glacial Lake Washburn and Palaeotemperatures in the McMurdo Dry Valleys, Antarctica, During the Last Glacial Maximum Author: Obryk, Maciej, Doran, Peter, Waddington, Ed, McKay, Chris Year: 2017 Large glacial lakes, including Glacial Lake Washburn, were present in the McMurdo Dry Valleys, Antarctica, during the Last Glacial Maximum (LGM) despite a colder and drier climate. To address the mechanism capable of generating enough meltwater to sustain these large lakes, a conceptual model was developed based on the warming potential of infrequent contemporary föhn winds. The model suggests that föhn winds were capable of generating enough meltwater to sustain large glacial lakes during the LGM by increasing degree days above freezing (DDAF) and prolonging the melt season. A present-day relationship between infrequent summer föhn winds and DDAF was established. It is assumed that the Taylor Dome ice core record represents large-scale palaeoclimatic variations for the McMurdo Dry Valleys region. This analysis suggests that because of the warming influence of the more frequent föhn winds, summer DDAF in the McMurdo Dry Valleys during the LGM were equivalent to present-day values, but this enhanced summer signal is not preserved in the annually averaged ice core temperature record. © Antarctic Science Ltd 2017 Close

• 38. [Article] Trajectory Analysis of Black Carbon in the Arctic Region

  Black carbon (BC) is a troubling particulate. Commonly known as soot, BC forms through the incomplete combustion of fossil fuels, biofuels, and biomass. It has a very low albedo compared to natural particulates ...

  Citation × Citation Citation Abstract Copy Title: Trajectory Analysis of Black Carbon in the Arctic Region Author: Gottschalk, Kimberly Year: 2016 Black carbon (BC) is a troubling particulate. Commonly known as soot, BC forms through the incomplete combustion of fossil fuels, biofuels, and biomass. It has a very low albedo compared to natural particulates making it a very efficient absorber of solar radiation. As BC is deposited on snow and ice, albedo is decreased - enhancing solar heating and increasing meltwater production. With rising air temperatures, melting rates of polar ice are increasing and are being enhanced by BC, leading to accelerated global sea level rise. This study aimed to document sources and deposition areas of BC in the Arctic. Utilizing HySplit, an air trajectory model, patterns of BC trajectories are assessed. Spatial patterns of deposition are estimated from known sources and source regions predicted from known deposition locations through the use of backward trajectory. Atmospheric circulation transports BC from temperate regions into the Arctic. The strength and location of the polar front in relation to the North Atlantic Oscillation is a dominant controlling factor. Preliminary results show reoccurring potential sources located in the Northeastern United States, Nova Scotia, Northern United Kingdom, and the Scandinavian Peninsula with large deposition events occurring within the first six months of the year. Title: Trajectory Analysis of Black Carbon in the Arctic Region Author: Gottschalk, Kimberly Year: 2016 Black carbon (BC) is a troubling particulate. Commonly known as soot, BC forms through the incomplete combustion of fossil fuels, biofuels, and biomass. It has a very low albedo compared to natural particulates making it a very efficient absorber of solar radiation. As BC is deposited on snow and ice, albedo is decreased - enhancing solar heating and increasing meltwater production. With rising air temperatures, melting rates of polar ice are increasing and are being enhanced by BC, leading to accelerated global sea level rise. This study aimed to document sources and deposition areas of BC in the Arctic. Utilizing HySplit, an air trajectory model, patterns of BC trajectories are assessed. Spatial patterns of deposition are estimated from known sources and source regions predicted from known deposition locations through the use of backward trajectory. Atmospheric circulation transports BC from temperate regions into the Arctic. The strength and location of the polar front in relation to the North Atlantic Oscillation is a dominant controlling factor. Preliminary results show reoccurring potential sources located in the Northeastern United States, Nova Scotia, Northern United Kingdom, and the Scandinavian Peninsula with large deposition events occurring within the first six months of the year. Close

• 39. [Article] Quantifying Twentieth Century Glacier Change in the Sierra Nevada, California

  Numerous small alpine glaciers occupy the high elevation regions of the central and southern Siena Nevada, California. These glaciers change size in response to variations in climate and are therefore ...

  Citation × Citation Citation Abstract Copy Title: Quantifying Twentieth Century Glacier Change in the Sierra Nevada, California Author: Basagic, Hassan J. Year: 2008 Numerous small alpine glaciers occupy the high elevation regions of the central and southern Siena Nevada, California. These glaciers change size in response to variations in climate and are therefore important indicators of climate change. An inventory based on USGS topographic maps (l :24,000) revealed 1719 glaciers and perennial snow and ice features for a total area of 39.l5 ±7.52 km2. The number of 'true' glaciers, versus non-moving ice, is estimated to be 118, covering 15.87 ± 1.69 Km2. All glaciers were located on north to northeast aspects, at elevations >3000 m. Historical photographs, geologic evidence, and field mapping were used to determine the magnitude of area loss over the past century at 14 glaciers. These glaciers decreased in area by 31% to 78%, averaging 55%. The rate of area change was determined for multiple time periods for a subset of seven glaciers. Rapid retreat occurred over the first half of the twentieth century beginning in the 1920s in response to warm/dry conditions and continued through the mid-1970s. Recession ceased during the early 1980s, when some glaciers advanced. Since the 1980s each of the seven study glaciers resumed retreat. The uniform timing of changes in area amongst study glaciers suggests a response to regional climate, while the magnitude of change is influenced by local topographic effects. Glacier area changes correlate with changes in spring and summer air temperatures. Winter precipitation is statistically unrelated to changes in glacier area. Headwall cliffs above the glaciers alter the glacier responses by reducing incoming shortwave radiation and enhancing snow accumulation via avalanching. Title: Quantifying Twentieth Century Glacier Change in the Sierra Nevada, California Author: Basagic, Hassan J. Year: 2008 Numerous small alpine glaciers occupy the high elevation regions of the central and southern Siena Nevada, California. These glaciers change size in response to variations in climate and are therefore important indicators of climate change. An inventory based on USGS topographic maps (l :24,000) revealed 1719 glaciers and perennial snow and ice features for a total area of 39.l5 ±7.52 km2. The number of 'true' glaciers, versus non-moving ice, is estimated to be 118, covering 15.87 ± 1.69 Km2. All glaciers were located on north to northeast aspects, at elevations >3000 m. Historical photographs, geologic evidence, and field mapping were used to determine the magnitude of area loss over the past century at 14 glaciers. These glaciers decreased in area by 31% to 78%, averaging 55%. The rate of area change was determined for multiple time periods for a subset of seven glaciers. Rapid retreat occurred over the first half of the twentieth century beginning in the 1920s in response to warm/dry conditions and continued through the mid-1970s. Recession ceased during the early 1980s, when some glaciers advanced. Since the 1980s each of the seven study glaciers resumed retreat. The uniform timing of changes in area amongst study glaciers suggests a response to regional climate, while the magnitude of change is influenced by local topographic effects. Glacier area changes correlate with changes in spring and summer air temperatures. Winter precipitation is statistically unrelated to changes in glacier area. Headwall cliffs above the glaciers alter the glacier responses by reducing incoming shortwave radiation and enhancing snow accumulation via avalanching. Close

• 40. [Article] Near-Surface Internal Melting: a Substantial Mass Loss on Antarctic Dry Valley Glaciers

  The McMurdo Dry Valleys, southern Victoria Land, East Antarctica, are a polar desert, and melt from glacial ice is the primary source of water to streams, lakes and associated ecosystems. Previous work ...

  Citation × Citation Citation Abstract Copy Title: Near-Surface Internal Melting: a Substantial Mass Loss on Antarctic Dry Valley Glaciers Author: Hoffman, Matthew J., Fountain, Andrew G., Liston, Glen E. Year: 2014 The McMurdo Dry Valleys, southern Victoria Land, East Antarctica, are a polar desert, and melt from glacial ice is the primary source of water to streams, lakes and associated ecosystems. Previous work found that to adequately model glacier ablation and subsurface ice temperatures with a surface energy-balance model required including the transmission of solar radiation into the ice. Here we investigate the contribution of subsurface melt to the mass balance of (and runoff from) Dry Valley glaciers by including a drainage process in the model and applying the model to three glacier sites using 13years of hourly meteorological data. Model results for the smooth glacier surfaces common to many glaciers in the Dry Valleys showed that sublimation was typically the largest component of surface lowering, with rare episodes of surface melting, consistent with anecdotal field observations. Results also showed extensive internal melting 5-15 cm below the ice surface, the drainage of which accounted for 50% of summer ablation. This is consistent with field observations of subsurface streams and formation of a weathering crust. We identify an annual cycle of weathering crust formation in summer and its removal during the 10 months of winter sublimation. Title: Near-Surface Internal Melting: a Substantial Mass Loss on Antarctic Dry Valley Glaciers Author: Hoffman, Matthew J., Fountain, Andrew G., Liston, Glen E. Year: 2014 The McMurdo Dry Valleys, southern Victoria Land, East Antarctica, are a polar desert, and melt from glacial ice is the primary source of water to streams, lakes and associated ecosystems. Previous work found that to adequately model glacier ablation and subsurface ice temperatures with a surface energy-balance model required including the transmission of solar radiation into the ice. Here we investigate the contribution of subsurface melt to the mass balance of (and runoff from) Dry Valley glaciers by including a drainage process in the model and applying the model to three glacier sites using 13years of hourly meteorological data. Model results for the smooth glacier surfaces common to many glaciers in the Dry Valleys showed that sublimation was typically the largest component of surface lowering, with rare episodes of surface melting, consistent with anecdotal field observations. Results also showed extensive internal melting 5-15 cm below the ice surface, the drainage of which accounted for 50% of summer ablation. This is consistent with field observations of subsurface streams and formation of a weathering crust. We identify an annual cycle of weathering crust formation in summer and its removal during the 10 months of winter sublimation. Close