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• 11. [Article] Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks

  Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. ...

  Citation × Citation Citation Abstract Copy Title: Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks Author: Hiester, Justin Year: 2013 Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. Recent satellite observations of ice surface elevation changes have given researchers new insights into how subglacial water is stored and transported. Localized uplift and settling of the ice surface implies that lakes exist beneath the ice sheet that are being filled and drained on relatively short time scales. %At the base of an ice sheet water can be transported through a variety of drainage networks or stored in subglacial lakes. Here, a numerical investigation of the mechanisms of transport and storage of subglacial water and the associated time scales is presented. Experiments are carried out using a finite element model of coupled ice and water flow. The first experiment seeks to understand the relationship between the depth of a basal depression and the area over which the feature affects basal water flow. It is found that as the perturbation to a topographic depression's depth is increased, water is rerouted in response to the perturbation. Additionally it is found that the relationship between perturbation depth and the extent upstream to which its effects reach is nonlinear. The second experiment examines how the aspect ratio of bed features (prolate, oblate, or equidimensional) influences basal water flow. It is found that the systems that develop and their interactions are mediated by both the topography and the feedbacks taken into account by the coupling of the systems in the model. Features oriented parallel to ice and water flow are associated with distributed fan systems that develop branches which migrate laterally across the domain and interact with one another on monthly and yearly timescales. Laterally oriented features develop laterally extensive ponds. As the ratio of longitudinal to lateral dimension of the topography is increased, a combination of these two water distributions is seen. Title: Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks Author: Hiester, Justin Year: 2013 Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. Recent satellite observations of ice surface elevation changes have given researchers new insights into how subglacial water is stored and transported. Localized uplift and settling of the ice surface implies that lakes exist beneath the ice sheet that are being filled and drained on relatively short time scales. %At the base of an ice sheet water can be transported through a variety of drainage networks or stored in subglacial lakes. Here, a numerical investigation of the mechanisms of transport and storage of subglacial water and the associated time scales is presented. Experiments are carried out using a finite element model of coupled ice and water flow. The first experiment seeks to understand the relationship between the depth of a basal depression and the area over which the feature affects basal water flow. It is found that as the perturbation to a topographic depression's depth is increased, water is rerouted in response to the perturbation. Additionally it is found that the relationship between perturbation depth and the extent upstream to which its effects reach is nonlinear. The second experiment examines how the aspect ratio of bed features (prolate, oblate, or equidimensional) influences basal water flow. It is found that the systems that develop and their interactions are mediated by both the topography and the feedbacks taken into account by the coupling of the systems in the model. Features oriented parallel to ice and water flow are associated with distributed fan systems that develop branches which migrate laterally across the domain and interact with one another on monthly and yearly timescales. Laterally oriented features develop laterally extensive ponds. As the ratio of longitudinal to lateral dimension of the topography is increased, a combination of these two water distributions is seen. Close

• 12. [Article] Introduction to Special Section on Microcosms in Ice: The Biogeochemistry of Cryoconite Holes

  Cryoconite holes are small, water filled, cylindrical melt-holes on glacial ice surface. Cryoconite, 'cold dust,' refers to the thin layer of sediment at the hole bottom. The holes form from surficial ...

  Citation × Citation Citation Abstract Copy Title: Introduction to Special Section on Microcosms in Ice: The Biogeochemistry of Cryoconite Holes Author: Fountain, Andrew G., Tranter, Martyn Year: 2008 Cryoconite holes are small, water filled, cylindrical melt-holes on glacial ice surface. Cryoconite, 'cold dust,' refers to the thin layer of sediment at the hole bottom. The holes form from surficial sediment patches that absorbs more solar radiation than the surrounding ice and which preferentially melt into the glacier forming a cylindrical water-filled hole. These holes form on the ice-covered, as opposed to snow covered, parts of glaciers world-wide, wherever there is sufficient energy for melting. Biogeochemically, cryoconite holes are interesting because the sediment is inncoculated with biologic material, a fraction of which thrives in the cryoconite environment of near-freezing waters and limited nutrient supply. The holes are thus oases for microbial life and biologically mediated chemical reactions on otherwise relatively inert glacier surfaces. Examining the chemical evolution of waters in cryoconite holes, showing how biogeochemical processes in cryoconite holes lead to increasing concentrations of dissolved organic carbon over time, which in may enhance adsorption of solar radiation by the water, aiding the development of deeper holes. If this is true, it suggests that there are a number of complex interactions between the biology, chemistry and biology of cryoconite holes, which act in concert to maintain life on glacier surfaces. Title: Introduction to Special Section on Microcosms in Ice: The Biogeochemistry of Cryoconite Holes Author: Fountain, Andrew G., Tranter, Martyn Year: 2008 Cryoconite holes are small, water filled, cylindrical melt-holes on glacial ice surface. Cryoconite, 'cold dust,' refers to the thin layer of sediment at the hole bottom. The holes form from surficial sediment patches that absorbs more solar radiation than the surrounding ice and which preferentially melt into the glacier forming a cylindrical water-filled hole. These holes form on the ice-covered, as opposed to snow covered, parts of glaciers world-wide, wherever there is sufficient energy for melting. Biogeochemically, cryoconite holes are interesting because the sediment is inncoculated with biologic material, a fraction of which thrives in the cryoconite environment of near-freezing waters and limited nutrient supply. The holes are thus oases for microbial life and biologically mediated chemical reactions on otherwise relatively inert glacier surfaces. Examining the chemical evolution of waters in cryoconite holes, showing how biogeochemical processes in cryoconite holes lead to increasing concentrations of dissolved organic carbon over time, which in may enhance adsorption of solar radiation by the water, aiding the development of deeper holes. If this is true, it suggests that there are a number of complex interactions between the biology, chemistry and biology of cryoconite holes, which act in concert to maintain life on glacier surfaces. Close

• 13. [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

• 14. [Article] Processes Controlling Carbon Cycling in Antarctic Glacier Surface Ecosystems

  Glacier surface ecosystems, including cryoconite holes and cryolakes, are significant contributors to regional carbon cycles. Incubation experiments to determine the net production (NEP) of organic matter ...

  Citation × Citation Citation Abstract Copy Title: Processes Controlling Carbon Cycling in Antarctic Glacier Surface Ecosystems Author: Bagshaw, Elizabeth A., Tranter, Martyn, Wadham, Jemma L., Fountain, Andrew G., Dubnick, A., Fitzsimons, S. Year: 2016 Glacier surface ecosystems, including cryoconite holes and cryolakes, are significant contributors to regional carbon cycles. Incubation experiments to determine the net production (NEP) of organic matter in cryoconite typically have durations of 6-24 hours, and produce a wide range of results, many of which indicate that the system is net heterotrophic. We employ longer term incubations to examine the temporal variation of NEP in cryoconite from the McMurdo Dry Valleys, Antarctica to examine the effect of sediment disturbance on system production, and to understand processes controlling production over the lifetimes of glacier surface ecosystems. The shorter-term incubations have durations of one week and show net heterotrophy. The longer term incubations of approximately one year show net autotrophy, but only after a period of about 40 days (~1000 hours). The control on net organic carbon production is a combination of the rate of diffusion of dissolved inorganic carbon from heterotrophic activity within cryoconite into the water, the rate of carbonate dissolution, and the saturation of carbonate in the water (which is a result of photosynthesis in a closed system). We demonstrate that sediment on glacier surfaces has the potential to accumulate carbon over timescales of months to years. Title: Processes Controlling Carbon Cycling in Antarctic Glacier Surface Ecosystems Author: Bagshaw, Elizabeth A., Tranter, Martyn, Wadham, Jemma L., Fountain, Andrew G., Dubnick, A., Fitzsimons, S. Year: 2016 Glacier surface ecosystems, including cryoconite holes and cryolakes, are significant contributors to regional carbon cycles. Incubation experiments to determine the net production (NEP) of organic matter in cryoconite typically have durations of 6-24 hours, and produce a wide range of results, many of which indicate that the system is net heterotrophic. We employ longer term incubations to examine the temporal variation of NEP in cryoconite from the McMurdo Dry Valleys, Antarctica to examine the effect of sediment disturbance on system production, and to understand processes controlling production over the lifetimes of glacier surface ecosystems. The shorter-term incubations have durations of one week and show net heterotrophy. The longer term incubations of approximately one year show net autotrophy, but only after a period of about 40 days (~1000 hours). The control on net organic carbon production is a combination of the rate of diffusion of dissolved inorganic carbon from heterotrophic activity within cryoconite into the water, the rate of carbonate dissolution, and the saturation of carbonate in the water (which is a result of photosynthesis in a closed system). We demonstrate that sediment on glacier surfaces has the potential to accumulate carbon over timescales of months to years. Close

• 15. [Article] A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica

  We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave ...

  Citation × Citation Citation Abstract Copy Title: A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica Author: Hunt, H. W., Fountain, Andrew G., Doran, Peter T., Basagic, Hassan J. Year: 2010 We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave and longwave radiation. Water fluxes included snowmelt, freezing/thawing of soil water, soil capillary flow, and vapour flows among atmosphere, soil, and snow. The model accounted for 96-99% of variation in soil temperature data. No long-term temporal trends in soil temperature were apparent. Soil water vapour concentration in thawed surface soil in summer often was higher than in frozen deeper soils, leading to downward vapour fluxes. Katabatic winds caused a reversal of the usual winter pattern of upward vapour fluxes. The model exhibited a steady state depth distribution of soil water due to vapour flows and in the absence of capillary flows below the top 0.5 cm soil layer. Beginning with a completely saturated soil profile, soil water was lost rapidly, and within a few hundred years approached a steady state characterized by dry soil (,0.5% gravimetric) down to one metre depth and saturated soil below that. In contrast, it took 42,000 years to approach steady state beginning from a completely dry initial condition. Title: A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica Author: Hunt, H. W., Fountain, Andrew G., Doran, Peter T., Basagic, Hassan J. Year: 2010 We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave and longwave radiation. Water fluxes included snowmelt, freezing/thawing of soil water, soil capillary flow, and vapour flows among atmosphere, soil, and snow. The model accounted for 96-99% of variation in soil temperature data. No long-term temporal trends in soil temperature were apparent. Soil water vapour concentration in thawed surface soil in summer often was higher than in frozen deeper soils, leading to downward vapour fluxes. Katabatic winds caused a reversal of the usual winter pattern of upward vapour fluxes. The model exhibited a steady state depth distribution of soil water due to vapour flows and in the absence of capillary flows below the top 0.5 cm soil layer. Beginning with a completely saturated soil profile, soil water was lost rapidly, and within a few hundred years approached a steady state characterized by dry soil (,0.5% gravimetric) down to one metre depth and saturated soil below that. In contrast, it took 42,000 years to approach steady state beginning from a completely dry initial condition. Close

• 16. [Article] Glacier Change on the Three Sisters Volcanoes, Oregon: 1900-2010

  A glacier responds to changes in climate by subsequent retreat and advance as a result of changes in snow inputs and outputs. Understanding these changes is important because shrinking glaciers limit and ...

  Citation × Citation Citation Abstract Copy Title: Glacier Change on the Three Sisters Volcanoes, Oregon: 1900-2010 Author: Ohlschlager, Justin George Year: 2015 A glacier responds to changes in climate by subsequent retreat and advance as a result of changes in snow inputs and outputs. Understanding these changes is important because shrinking glaciers limit and diminish local water resources. They contribute to alpine runoff in the late-summer months by delaying the maximum runoff until late in the melt season. A comprehensive glacier and perennial snowfield inventory has not been completed for the Three Sisters in Central Oregon. Using aerial photography, Digital Elevation Models (DEMs), previous studies, and historical ground based photographs these glacier and perennial snowfields were defined and their surface area change was quantified along with surface area and volume change for the 15 named glaciers for multiple years. The glaciers and perennial snowfields totaled 9.03 ± 1.65 km2 in 1949 and decreased to 7.1 ± 1.16 km2 in 2003 giving a total loss of -1.914 ± 0.974 km2 ( 21%). The 15 named glaciers totaled 12.43 ± 0.417 km2 in ~1900 and decreased to 5.65 ± 0.135 km2 in 2003 giving a total loss of -6.70 ± 0.439 km2 (54%) with more loss occurring in the early part of the century. It's estimated that the 15 named glaciers lost roughly 61% of volume from 1900 to 2010. From 1957 to 2010 their surface's dropped in elevation on average by -8.9m, losing an estimated 71.96 x 106 ± 2.87 x 106 m3 (53%) in total volume, seen across accumulation and ablation zones, with more loss happening from 1957 to 1990. There was no relationship found between topography and area. A small correlation was found between slope and increased volume change. Debris cover on glacier surfaces has increased and showed a correlation between decreasing area loss (no correlation with volume changes). Title: Glacier Change on the Three Sisters Volcanoes, Oregon: 1900-2010 Author: Ohlschlager, Justin George Year: 2015 A glacier responds to changes in climate by subsequent retreat and advance as a result of changes in snow inputs and outputs. Understanding these changes is important because shrinking glaciers limit and diminish local water resources. They contribute to alpine runoff in the late-summer months by delaying the maximum runoff until late in the melt season. A comprehensive glacier and perennial snowfield inventory has not been completed for the Three Sisters in Central Oregon. Using aerial photography, Digital Elevation Models (DEMs), previous studies, and historical ground based photographs these glacier and perennial snowfields were defined and their surface area change was quantified along with surface area and volume change for the 15 named glaciers for multiple years. The glaciers and perennial snowfields totaled 9.03 ± 1.65 km2 in 1949 and decreased to 7.1 ± 1.16 km2 in 2003 giving a total loss of -1.914 ± 0.974 km2 ( 21%). The 15 named glaciers totaled 12.43 ± 0.417 km2 in ~1900 and decreased to 5.65 ± 0.135 km2 in 2003 giving a total loss of -6.70 ± 0.439 km2 (54%) with more loss occurring in the early part of the century. It's estimated that the 15 named glaciers lost roughly 61% of volume from 1900 to 2010. From 1957 to 2010 their surface's dropped in elevation on average by -8.9m, losing an estimated 71.96 x 106 ± 2.87 x 106 m3 (53%) in total volume, seen across accumulation and ablation zones, with more loss happening from 1957 to 1990. There was no relationship found between topography and area. A small correlation was found between slope and increased volume change. Debris cover on glacier surfaces has increased and showed a correlation between decreasing area loss (no correlation with volume changes). Close

• 17. [Article] Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica

  A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative ...

  Citation × Citation Citation Abstract Copy Title: Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica Author: Obryk, Maciej K., Doran, Peter T., Hicks, Jared A., McKay, Christopher P., Priscu, John Charles Year: 2016 A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 a (between 1996 and 2012) of ice thickness changes for the west lobe of Lake Bonney (average ice thickness = 3.53 m) and Lake Fryxell (average ice thickness = 4.22 m). Long-term ice thick-ness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or fa-cilitate ice thickness change depending on the predominant climatic trend (cooling or warming). As such, shallow (columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation. Title: Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica Author: Obryk, Maciej K., Doran, Peter T., Hicks, Jared A., McKay, Christopher P., Priscu, John Charles Year: 2016 A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 a (between 1996 and 2012) of ice thickness changes for the west lobe of Lake Bonney (average ice thickness = 3.53 m) and Lake Fryxell (average ice thickness = 4.22 m). Long-term ice thick-ness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or fa-cilitate ice thickness change depending on the predominant climatic trend (cooling or warming). As such, shallow (columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation. Close

• 18. [Article] 'Sticky spots' and subglacial lakes under ice streams of the Siple Coast, Antarctica

  Locations of subglacial lakes discovered under fast-moving West Antarctic ice streams tend to be associated with topographic features of the subglacial bed or with areas that have strong variations in ...

  Citation × Citation Citation Abstract Copy Title: 'Sticky spots' and subglacial lakes under ice streams of the Siple Coast, Antarctica Author: Sergienko, Olga V., Hulbe, Christina L. Year: 2011 Locations of subglacial lakes discovered under fast-moving West Antarctic ice streams tend to be associated with topographic features of the subglacial bed or with areas that have strong variations in basal conditions. Inversion of ice-stream surface velocity indicates that basal conditions under ice streams can be highly variable and that there can be widespread regions where basal traction is high. To seek an explanation for why lakes appear to be sited near areas with high basal traction, we use numerical models to simulate ice-stream dynamics, thermodynamics and subglacial water flow. We demonstrate that the ice flow over high basal traction areas produces favourable conditions for the ponding of meltwater. Energy dissipation associated with ice sliding over a region with high basal traction constitutes a water source supplying a lake, and ice-thickness perturbations induced by ice flow over variable traction create local minima in hydraulic potential. Variations in thermodynamic processes caused by such ice flow could be responsible for limiting the horizontal extent of the subglacial lakes. Title: 'Sticky spots' and subglacial lakes under ice streams of the Siple Coast, Antarctica Author: Sergienko, Olga V., Hulbe, Christina L. Year: 2011 Locations of subglacial lakes discovered under fast-moving West Antarctic ice streams tend to be associated with topographic features of the subglacial bed or with areas that have strong variations in basal conditions. Inversion of ice-stream surface velocity indicates that basal conditions under ice streams can be highly variable and that there can be widespread regions where basal traction is high. To seek an explanation for why lakes appear to be sited near areas with high basal traction, we use numerical models to simulate ice-stream dynamics, thermodynamics and subglacial water flow. We demonstrate that the ice flow over high basal traction areas produces favourable conditions for the ponding of meltwater. Energy dissipation associated with ice sliding over a region with high basal traction constitutes a water source supplying a lake, and ice-thickness perturbations induced by ice flow over variable traction create local minima in hydraulic potential. Variations in thermodynamic processes caused by such ice flow could be responsible for limiting the horizontal extent of the subglacial lakes. Close

• 19. [Article] The Link Between Climate Warming and Break-Up of Ice Shelves in the Antarctic Peninsula

  A review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; ...

  Citation × Citation Citation Abstract Copy Title: The Link Between Climate Warming and Break-Up of Ice Shelves in the Antarctic Peninsula Author: Scambos, Ted A., Hulbe, Christina L., Fahnestock, Mark A., Bohlander, Jennifer Year: 2000 A review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; calving of myriad small elongate bergs in punctuated events; increasing flow speed; and the presence of melt ponds on the ice-shelf surface in the vicinity of the break-ups. As climate has warmed in the Antarctic Peninsula region, melt-season duration and the extent of ponding have increased. Most break-up events have occurred during longer melt seasons, suggesting that meltwater itself, not just warming, is responsible. Regions that show melting without pond formation are relatively unchanged. Melt ponds thus appear to be a robust harbinger of ice-shelf retreat. We use these observations to guide a model of ice-shelf flow and the effects of meltwater. Crevasses present in a region of surface ponding will likely fill to the brim with water. We hypothesize (building on Weertman (1973), Hughes (1983) and Van der Veen (1998)) that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat. A thermodynamic finite-element model is used to evaluate ice flow and the strain field, and simple extensions of this model are used to investigate crack propagation by meltwater. The model results support the hypothesis. Title: The Link Between Climate Warming and Break-Up of Ice Shelves in the Antarctic Peninsula Author: Scambos, Ted A., Hulbe, Christina L., Fahnestock, Mark A., Bohlander, Jennifer Year: 2000 A review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; calving of myriad small elongate bergs in punctuated events; increasing flow speed; and the presence of melt ponds on the ice-shelf surface in the vicinity of the break-ups. As climate has warmed in the Antarctic Peninsula region, melt-season duration and the extent of ponding have increased. Most break-up events have occurred during longer melt seasons, suggesting that meltwater itself, not just warming, is responsible. Regions that show melting without pond formation are relatively unchanged. Melt ponds thus appear to be a robust harbinger of ice-shelf retreat. We use these observations to guide a model of ice-shelf flow and the effects of meltwater. Crevasses present in a region of surface ponding will likely fill to the brim with water. We hypothesize (building on Weertman (1973), Hughes (1983) and Van der Veen (1998)) that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat. A thermodynamic finite-element model is used to evaluate ice flow and the strain field, and simple extensions of this model are used to investigate crack propagation by meltwater. The model results support the hypothesis. Close

• 20. [Article] Patterns and Processes of Salt Efflorescences in the McMurdo region, Antarctica

  Evaporite salts are abundant around the McMurdo region, Antarctica (~78°S) due to very low precipitation, low relative humidity, and limited overland flow. Hygroscopic salts in the McMurdo Dry Valleys ...

  Citation × Citation Citation Abstract Copy Title: Patterns and Processes of Salt Efflorescences in the McMurdo region, Antarctica Author: Bisson, Kelsey M., Welch, Kathleen A., Welch, Susan A., Sheets, Julia Meyer, Lyons, W. Berry, Levy, Joseph S., Fountain, Andrew G. Year: 2015 Evaporite salts are abundant around the McMurdo region, Antarctica (~78°S) due to very low precipitation, low relative humidity, and limited overland flow. Hygroscopic salts in the McMurdo Dry Valleys (MDVs) are preferentially formed in locations where liquid water is present in the austral summer, including along ephemeral streams, ice-covered lake boundaries, or shallow groundwater tracks. In this study, we collected salts from the Miers, Garwood, and Taylor Valleys on the Antarctic continent, as well as around McMurdo Station on Ross Island in close proximity to water sources with the goal of understanding salt geochemistry in relationship to the hydrology of the area. Halite is ubiquitous; sodium is the major cation (ranging from 70%–90% of cations by meq kg-1 sediment) and chloride is the major anion (>50%) in nearly all samples. However, a wide variety of salt phases and morphologies are tentatively identified through scanning electron microscopy (SEM) and X-ray diffraction (XRD) work. We present new data that identifies trona (Na3(CO3)(HCO3)·2H2O), tentative gaylussite (Na2Ca(CO3)2·5H2O), and tentative glauberite (Na2Ca(SO4)2) in the MDV, of which the later one has not been documented previously. Our work allows for the evaluation of processes that influence brine evolution on a local scale, consequently informing assumptions underlying large-scale processes (such as paleoclimate) in the MDV. Hydrological modeling conducted in FREZCHEM and PHREEQC suggests that a model based on aerosol deposition alone in low elevations on the valley floor inadequately characterizes salt distributions found on the surfaces of the soil because it does not account for other hydrologic inputs/outputs. Implications for the salt distributions include their use as tracers for paleolake levels, geochemical tracers of ephemeral water tracks or “wet patches” in the soil, indicators of chemical weathering products, and potential delineators of ecological communities. Title: Patterns and Processes of Salt Efflorescences in the McMurdo region, Antarctica Author: Bisson, Kelsey M., Welch, Kathleen A., Welch, Susan A., Sheets, Julia Meyer, Lyons, W. Berry, Levy, Joseph S., Fountain, Andrew G. Year: 2015 Evaporite salts are abundant around the McMurdo region, Antarctica (~78°S) due to very low precipitation, low relative humidity, and limited overland flow. Hygroscopic salts in the McMurdo Dry Valleys (MDVs) are preferentially formed in locations where liquid water is present in the austral summer, including along ephemeral streams, ice-covered lake boundaries, or shallow groundwater tracks. In this study, we collected salts from the Miers, Garwood, and Taylor Valleys on the Antarctic continent, as well as around McMurdo Station on Ross Island in close proximity to water sources with the goal of understanding salt geochemistry in relationship to the hydrology of the area. Halite is ubiquitous; sodium is the major cation (ranging from 70%–90% of cations by meq kg-1 sediment) and chloride is the major anion (>50%) in nearly all samples. However, a wide variety of salt phases and morphologies are tentatively identified through scanning electron microscopy (SEM) and X-ray diffraction (XRD) work. We present new data that identifies trona (Na3(CO3)(HCO3)·2H2O), tentative gaylussite (Na2Ca(CO3)2·5H2O), and tentative glauberite (Na2Ca(SO4)2) in the MDV, of which the later one has not been documented previously. Our work allows for the evaluation of processes that influence brine evolution on a local scale, consequently informing assumptions underlying large-scale processes (such as paleoclimate) in the MDV. Hydrological modeling conducted in FREZCHEM and PHREEQC suggests that a model based on aerosol deposition alone in low elevations on the valley floor inadequately characterizes salt distributions found on the surfaces of the soil because it does not account for other hydrologic inputs/outputs. Implications for the salt distributions include their use as tracers for paleolake levels, geochemical tracers of ephemeral water tracks or “wet patches” in the soil, indicators of chemical weathering products, and potential delineators of ecological communities. Close