The Experts below are selected from a list of 2088 Experts worldwide ranked by ideXlab platform
Donald Slater - One of the best experts on this subject based on the ideXlab platform.
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Estimating Greenland Tidewater Glacier retreat driven by submarine melting
The Cryosphere, 2019Co-Authors: Donald Slater, Fiamma Straneo, Denis Felikson, Christopher M. Little, Heiko Goelzer, Xavier Fettweis, James HolteAbstract:Abstract. The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's Tidewater Glacier calving fronts is thought to be a key driver of widespread Glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice-sheet-scale models. Here we propose parameterizing Tidewater Glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial discharge and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, subglacial discharge and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–2018. We demonstrate a statistically significant link between multi-decadal Tidewater Glacier terminus position change and submarine melting and show that the proposed parameterization has predictive power when considering a population of Glaciers. An illustrative 21st century projection is considered, suggesting that Tidewater Glaciers in Greenland will undergo little further retreat in a low-emission RCP2.6 scenario. In contrast, a high-emission RCP8.5 scenario results in a median retreat of 4.2 km, with a quarter of Tidewater Glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice-sheet-wide assessment of the sensitivity of Tidewater Glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet.
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localized plumes drive front wide ocean melting of a greenlandic Tidewater Glacier
Geophysical Research Letters, 2018Co-Authors: Donald Slater, Fiammetta Straneo, Sarah B Das, Clark Richards, Till J W Wagner, Peter NienowAbstract:Support was provided by the National Science Foundation (NSF) through PLR-1418256 and PLR-1744835, and through Woods Hole Oceanographic Institution (WHOI) Ocean and Climate Change Institute (OCCI) and the Clark Foundation. This work was also supported by a UK Natural Environmental Research Council (NERC) PhD studentship (NE/L501566/1) and Scottish Alliance for Geoscience, Environment & Society (SAGES) early career research exchange funding to D. A. S.
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linear response of east greenland s Tidewater Glaciers to ocean atmosphere warming
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Donald Slater, Tom Cowton, Andrew Sole, Peter Nienow, Poul ChristoffersenAbstract:Predicting the retreat of Tidewater outlet Glaciers forms a major obstacle to forecasting the rate of mass loss from the Greenland Ice Sheet. This reflects the challenges of modeling the highly dynamic, topographically complex, and data-poor environment of the Glacier-fjord systems that link the ice sheet to the ocean. To avoid these difficulties, we investigate the extent to which Tidewater Glacier retreat can be explained by simple variables: air temperature, meltwater runoff, ocean temperature, and two simple parameterizations of "ocean/atmosphere" forcing based on the combined influence of runoff and ocean temperature. Over a 20-y period at 10 large Tidewater outlet Glaciers along the east coast of Greenland, we find that ocean/atmosphere forcing can explain up to 76% of the variability in terminus position at individual Glaciers and 54% of variation in terminus position across all 10 Glaciers. Our findings indicate that (i) the retreat of east Greenland's Tidewater Glaciers is best explained as a product of both oceanic and atmospheric warming and (ii) despite the complexity of Tidewater Glacier behavior, over multiyear timescales a significant proportion of terminus position change can be explained as a simple function of this forcing. These findings thus demonstrate that simple parameterizations can play an important role in predicting the response of the ice sheet to future climate warming.
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estimating spring terminus submarine melt rates at a greenlandic Tidewater Glacier using satellite imagery
EGU General Assembly Conference Abstracts, 2018Co-Authors: Alexis Moyer, Donald Slater, Andrew Sole, Peter Nienow, Noel GourmelenAbstract:Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at Tidewater Glaciers, with submarine melting proposed as a potential trigger of increased Glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving Glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d−1 near the Glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d−1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at Tidewater Glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
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estimating spring terminus submarine melt rates at a greenlandic Tidewater Glacier using satellite imagery
Frontiers in Earth Science, 2017Co-Authors: Alexis Moyer, Donald Slater, Andrew Sole, Peter Nienow, Noel GourmelenAbstract:Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at Tidewater Glaciers, with submarine melting proposed as a potential trigger of increased Glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving Glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia at the head of Kangersuneq Fjord, southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models, in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d^-1 near the Glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d^1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates at Tidewater Glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
Andrew Sole - One of the best experts on this subject based on the ideXlab platform.
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iceberg melting substantially modifies oceanic heat flux towards a major greenlandic Tidewater Glacier
Nature Communications, 2020Co-Authors: Benjamin Joseph Davison, Tom Cowton, Finlo Cottier, Andrew SoleAbstract:Fjord dynamics influence oceanic heat flux to the Greenland ice sheet. Submarine iceberg melting releases large volumes of freshwater within Greenland’s fjords, yet its impact on fjord dynamics remains unclear. We modify an ocean model to simulate submarine iceberg melting in Sermilik Fjord, east Greenland. Here we find that submarine iceberg melting cools and freshens the fjord by up to ~5 °C and 0.7 psu in the upper 100-200 m. The release of freshwater from icebergs drives an overturning circulation, resulting in a ~10% increase in net up-fjord heat flux. In addition, we find that submarine iceberg melting accounts for over 95% of heat used for ice melt in Sermilik Fjord. Our results highlight the substantial impact that icebergs have on the dynamics of a major Greenlandic fjord, demonstrating the importance of including related processes in studies that seek to quantify interactions between the ice sheet and the ocean. Iceberg melting releases large volumes of freshwater in fjords, yet the impact on oceanic heat delivery to Tidewater Glaciers is unknown. Here the authors show that iceberg melting invigorates fjord circulation in a large, iceberg-congested fjord, thereby increasing oceanic heat delivery to its Tidewater Glaciers.
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linear response of east greenland s Tidewater Glaciers to ocean atmosphere warming
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Donald Slater, Tom Cowton, Andrew Sole, Peter Nienow, Poul ChristoffersenAbstract:Predicting the retreat of Tidewater outlet Glaciers forms a major obstacle to forecasting the rate of mass loss from the Greenland Ice Sheet. This reflects the challenges of modeling the highly dynamic, topographically complex, and data-poor environment of the Glacier-fjord systems that link the ice sheet to the ocean. To avoid these difficulties, we investigate the extent to which Tidewater Glacier retreat can be explained by simple variables: air temperature, meltwater runoff, ocean temperature, and two simple parameterizations of "ocean/atmosphere" forcing based on the combined influence of runoff and ocean temperature. Over a 20-y period at 10 large Tidewater outlet Glaciers along the east coast of Greenland, we find that ocean/atmosphere forcing can explain up to 76% of the variability in terminus position at individual Glaciers and 54% of variation in terminus position across all 10 Glaciers. Our findings indicate that (i) the retreat of east Greenland's Tidewater Glaciers is best explained as a product of both oceanic and atmospheric warming and (ii) despite the complexity of Tidewater Glacier behavior, over multiyear timescales a significant proportion of terminus position change can be explained as a simple function of this forcing. These findings thus demonstrate that simple parameterizations can play an important role in predicting the response of the ice sheet to future climate warming.
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estimating spring terminus submarine melt rates at a greenlandic Tidewater Glacier using satellite imagery
EGU General Assembly Conference Abstracts, 2018Co-Authors: Alexis Moyer, Donald Slater, Andrew Sole, Peter Nienow, Noel GourmelenAbstract:Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at Tidewater Glaciers, with submarine melting proposed as a potential trigger of increased Glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving Glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d−1 near the Glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d−1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at Tidewater Glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
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estimating spring terminus submarine melt rates at a greenlandic Tidewater Glacier using satellite imagery
Frontiers in Earth Science, 2017Co-Authors: Alexis Moyer, Donald Slater, Andrew Sole, Peter Nienow, Noel GourmelenAbstract:Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at Tidewater Glaciers, with submarine melting proposed as a potential trigger of increased Glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving Glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia at the head of Kangersuneq Fjord, southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models, in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d^-1 near the Glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d^1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates at Tidewater Glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
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a model for Tidewater Glacier undercutting by submarine melting
Geophysical Research Letters, 2017Co-Authors: Donald Slater, Tom Cowton, Peter Nienow, Daniel Goldberg, Andrew SoleAbstract:Dynamic change at the marine-terminating margins of the Greenland Ice Sheet may be initiated by the ocean, particularly where subglacial runoff drives vigorous ice-marginal plumes and rapid submarine melting. Here we model submarine melt-driven undercutting of Tidewater Glacier termini, simulating a process which is key to understanding ice-ocean coupling. Where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area. Thus, the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice-ocean interface. We suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume, likely promoting calving of ice above. It remains unclear, however, whether undercutting proceeds sufficiently rapidly to influence calving at Greenland's fastest-flowing Glaciers.
Peter Nienow - One of the best experts on this subject based on the ideXlab platform.
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localized plumes drive front wide ocean melting of a greenlandic Tidewater Glacier
Geophysical Research Letters, 2018Co-Authors: Donald Slater, Fiammetta Straneo, Sarah B Das, Clark Richards, Till J W Wagner, Peter NienowAbstract:Support was provided by the National Science Foundation (NSF) through PLR-1418256 and PLR-1744835, and through Woods Hole Oceanographic Institution (WHOI) Ocean and Climate Change Institute (OCCI) and the Clark Foundation. This work was also supported by a UK Natural Environmental Research Council (NERC) PhD studentship (NE/L501566/1) and Scottish Alliance for Geoscience, Environment & Society (SAGES) early career research exchange funding to D. A. S.
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linear response of east greenland s Tidewater Glaciers to ocean atmosphere warming
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Donald Slater, Tom Cowton, Andrew Sole, Peter Nienow, Poul ChristoffersenAbstract:Predicting the retreat of Tidewater outlet Glaciers forms a major obstacle to forecasting the rate of mass loss from the Greenland Ice Sheet. This reflects the challenges of modeling the highly dynamic, topographically complex, and data-poor environment of the Glacier-fjord systems that link the ice sheet to the ocean. To avoid these difficulties, we investigate the extent to which Tidewater Glacier retreat can be explained by simple variables: air temperature, meltwater runoff, ocean temperature, and two simple parameterizations of "ocean/atmosphere" forcing based on the combined influence of runoff and ocean temperature. Over a 20-y period at 10 large Tidewater outlet Glaciers along the east coast of Greenland, we find that ocean/atmosphere forcing can explain up to 76% of the variability in terminus position at individual Glaciers and 54% of variation in terminus position across all 10 Glaciers. Our findings indicate that (i) the retreat of east Greenland's Tidewater Glaciers is best explained as a product of both oceanic and atmospheric warming and (ii) despite the complexity of Tidewater Glacier behavior, over multiyear timescales a significant proportion of terminus position change can be explained as a simple function of this forcing. These findings thus demonstrate that simple parameterizations can play an important role in predicting the response of the ice sheet to future climate warming.
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estimating spring terminus submarine melt rates at a greenlandic Tidewater Glacier using satellite imagery
EGU General Assembly Conference Abstracts, 2018Co-Authors: Alexis Moyer, Donald Slater, Andrew Sole, Peter Nienow, Noel GourmelenAbstract:Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at Tidewater Glaciers, with submarine melting proposed as a potential trigger of increased Glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving Glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d−1 near the Glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d−1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at Tidewater Glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
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estimating spring terminus submarine melt rates at a greenlandic Tidewater Glacier using satellite imagery
Frontiers in Earth Science, 2017Co-Authors: Alexis Moyer, Donald Slater, Andrew Sole, Peter Nienow, Noel GourmelenAbstract:Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at Tidewater Glaciers, with submarine melting proposed as a potential trigger of increased Glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving Glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia at the head of Kangersuneq Fjord, southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models, in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d^-1 near the Glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d^1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates at Tidewater Glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
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a model for Tidewater Glacier undercutting by submarine melting
Geophysical Research Letters, 2017Co-Authors: Donald Slater, Tom Cowton, Peter Nienow, Daniel Goldberg, Andrew SoleAbstract:Dynamic change at the marine-terminating margins of the Greenland Ice Sheet may be initiated by the ocean, particularly where subglacial runoff drives vigorous ice-marginal plumes and rapid submarine melting. Here we model submarine melt-driven undercutting of Tidewater Glacier termini, simulating a process which is key to understanding ice-ocean coupling. Where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area. Thus, the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice-ocean interface. We suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume, likely promoting calving of ice above. It remains unclear, however, whether undercutting proceeds sufficiently rapidly to influence calving at Greenland's fastest-flowing Glaciers.
Regine Hock - One of the best experts on this subject based on the ideXlab platform.
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variations in alaska Tidewater Glacier frontal ablation 1985 2013
Journal of Geophysical Research, 2015Co-Authors: Robert Mcnabb, Regine Hock, Matthias HussAbstract:Our incomplete knowledge of the proportion of mass loss due to frontal ablation (the sum of ice loss through calving and submarine melt) from Tidewater Glaciers outside of the Greenland and Antarctic ice sheets has been cited as a major hindrance to accurate predictions of global sea level rise. We present a 28 year record (1985–2013) of frontal ablation for 27 Alaska Tidewater Glaciers (representing 96% of the total Tidewater Glacier area in the region), calculated from satellite-derived ice velocities and modeled estimates of Glacier ice thickness. We account for cross-sectional ice thickness variation, long-term thickness changes, mass lost between an upstream fluxgate and the terminus, and mass change due to changes in terminus position. The total mean rate of frontal ablation for these 27 Glaciers over the period 1985–2013 is 15.11 ± 3.63Gta−1. Two Glaciers, Hubbard and Columbia, account for approximately 50% of these losses. The regional total ablation has decreased at a rate of 0.14Gta−1 over this time period, likely due to the slowing and thinning of many of the Glaciers in the study area. Frontal ablation constitutes only ∼4% of the total annual regional ablation, but roughly 20% of net mass loss. Comparing several commonly used approximations in the calculation of frontal ablation, we find that neglecting cross-sectional thickness variations severely underestimates frontal ablation.
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alaska Tidewater Glacier terminus positions 1948 2012
Journal of Geophysical Research, 2014Co-Authors: Robert Mcnabb, Regine HockAbstract:A significant portion of the world's Glacier ice drains through Tidewater outlets, though much remains unknown about the response to recent climate change of Tidewater Glaciers. We present a 64 year record of length change for 50 Alaska Tidewater Glaciers. We use U.S. Geological Survey topographic maps to provide a base length for Glaciers before 1970. Using all available cloud-free Landsat images, we manually digitize calving front outlines for each Glacier between 1972 and 2012, resulting in a total of more than 10,000 outlines. Tidewater Glacier lengths vary seasonally; focusing on the 36 Glaciers terminating in Tidewater throughout the study period, we find a mean (± standard deviation) seasonal variation of 60± 85 m a−1. We use these oscillations to determine the significance of interannual changes in Glacier length. All 36 Glaciers underwent at least one period (≥1 year) of significant advance or retreat; 28 Glaciers underwent at least one period of both significant advance and retreat. Over the entire period 1948–2012, 24 of these Glaciers retreated a total (± uncertainty) of 107.95±0.29 km, 11 advanced a total of 7.71±0.20, and one (Chenega Glacier) did not change significantly. Retreats and advances are highly variable in time; several Glaciers underwent rapid, short-term retreats of a few years duration. These retreats occurred after large changes in summer sea surface temperature anomalies; further study is needed to determine what triggered these retreats. No coherent regional behavior signal is apparent in the length record, although two subregions show a coherence similar to recent observations in Greenland.
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using surface velocities to calculate ice thickness and bed topography a case study at columbia Glacier alaska usa
Journal of Glaciology, 2012Co-Authors: Robert Mcnabb, Regine Hock, Shad Oneel, L A Rasmussen, Yushin Ahn, Matthias Braun, H Conway, Sam Herreid, Ian Joughin, W. T. PfefferAbstract:Information about Glacier volume and ice thickness distribution is essential for many glaciological applications, but direct measurements of ice thickness can be difficult and costly. We present a new method that calculates ice thickness via an estimate of ice flux. We solve the familiar continuity equation between adjacent flowlines, which decreases the computational time required compared to a solution on the whole grid. We test the method on Columbia Glacier, a large Tidewater Glacier in Alaska, USA, and compare calculated and measured ice thicknesses, with favorable results. This shows the potential of this method for estimating ice thickness distribution of Glaciers for which only surface data are available. We find that both the mean thickness and volume of Columbia Glacier were approximately halved over the period 1957-2007, from 281m to 143m, and from 294km 3 to 134km 3 , respectively. Using bedrock slope and considering how waves of thickness change propagate through the Glacier, we conduct a brief analysis of the instability of Columbia Glacier, which leads us to conclude that the rapid portion of the retreat may be nearing an end.
Tom Cowton - One of the best experts on this subject based on the ideXlab platform.
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iceberg melting substantially modifies oceanic heat flux towards a major greenlandic Tidewater Glacier
Nature Communications, 2020Co-Authors: Benjamin Joseph Davison, Tom Cowton, Finlo Cottier, Andrew SoleAbstract:Fjord dynamics influence oceanic heat flux to the Greenland ice sheet. Submarine iceberg melting releases large volumes of freshwater within Greenland’s fjords, yet its impact on fjord dynamics remains unclear. We modify an ocean model to simulate submarine iceberg melting in Sermilik Fjord, east Greenland. Here we find that submarine iceberg melting cools and freshens the fjord by up to ~5 °C and 0.7 psu in the upper 100-200 m. The release of freshwater from icebergs drives an overturning circulation, resulting in a ~10% increase in net up-fjord heat flux. In addition, we find that submarine iceberg melting accounts for over 95% of heat used for ice melt in Sermilik Fjord. Our results highlight the substantial impact that icebergs have on the dynamics of a major Greenlandic fjord, demonstrating the importance of including related processes in studies that seek to quantify interactions between the ice sheet and the ocean. Iceberg melting releases large volumes of freshwater in fjords, yet the impact on oceanic heat delivery to Tidewater Glaciers is unknown. Here the authors show that iceberg melting invigorates fjord circulation in a large, iceberg-congested fjord, thereby increasing oceanic heat delivery to its Tidewater Glaciers.
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linear response of east greenland s Tidewater Glaciers to ocean atmosphere warming
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Donald Slater, Tom Cowton, Andrew Sole, Peter Nienow, Poul ChristoffersenAbstract:Predicting the retreat of Tidewater outlet Glaciers forms a major obstacle to forecasting the rate of mass loss from the Greenland Ice Sheet. This reflects the challenges of modeling the highly dynamic, topographically complex, and data-poor environment of the Glacier-fjord systems that link the ice sheet to the ocean. To avoid these difficulties, we investigate the extent to which Tidewater Glacier retreat can be explained by simple variables: air temperature, meltwater runoff, ocean temperature, and two simple parameterizations of "ocean/atmosphere" forcing based on the combined influence of runoff and ocean temperature. Over a 20-y period at 10 large Tidewater outlet Glaciers along the east coast of Greenland, we find that ocean/atmosphere forcing can explain up to 76% of the variability in terminus position at individual Glaciers and 54% of variation in terminus position across all 10 Glaciers. Our findings indicate that (i) the retreat of east Greenland's Tidewater Glaciers is best explained as a product of both oceanic and atmospheric warming and (ii) despite the complexity of Tidewater Glacier behavior, over multiyear timescales a significant proportion of terminus position change can be explained as a simple function of this forcing. These findings thus demonstrate that simple parameterizations can play an important role in predicting the response of the ice sheet to future climate warming.
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a model for Tidewater Glacier undercutting by submarine melting
Geophysical Research Letters, 2017Co-Authors: Donald Slater, Tom Cowton, Peter Nienow, Daniel Goldberg, Andrew SoleAbstract:Dynamic change at the marine-terminating margins of the Greenland Ice Sheet may be initiated by the ocean, particularly where subglacial runoff drives vigorous ice-marginal plumes and rapid submarine melting. Here we model submarine melt-driven undercutting of Tidewater Glacier termini, simulating a process which is key to understanding ice-ocean coupling. Where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area. Thus, the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice-ocean interface. We suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume, likely promoting calving of ice above. It remains unclear, however, whether undercutting proceeds sufficiently rapidly to influence calving at Greenland's fastest-flowing Glaciers.
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spatially distributed runoff at the grounding line of a large greenlandic Tidewater Glacier inferred from plume modelling
Journal of Glaciology, 2017Co-Authors: Donald Slater, Tom Cowton, Andrew Sole, Peter Nienow, Ruth Mottram, Peter L Langen, Douglas MairAbstract:Understanding the drivers of recent change at Greenlandic Tidewater Glaciers is of great importance if we are to predict how these Glaciers will respond to climatic warming. A poorly constrained component of Tidewater Glacier processes is the near-terminus subglacial hydrology. Here we present a novel method for constraining near-terminus subglacial hydrology with application to marine-terminating Kangiata Nunata Sermia in South-west Greenland. By simulating proglacial plume dynamics using buoyant plume theory and a general circulation model, we assess the critical subglacial discharge, if delivered through a single compact channel, required to generate a plume that reaches the fjord surface. We then compare catchment runoff to a time series of plume visibility acquired from a time-lapse camera. We identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface, yet we observe no plume. We attribute these observations to spatial spreading of runoff across the grounding line. Persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers, potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive Tidewater Glacier acceleration.
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effect of near terminus subglacial hydrology on Tidewater Glacier submarine melt rates
Geophysical Research Letters, 2015Co-Authors: Donald Slater, Tom Cowton, Peter Nienow, Daniel Goldberg, Andrew SoleAbstract:Submarine melting of Greenlandic Tidewater Glacier termini is proposed as a possible mechanism driving their recent thinning and retreat. We use a general circulation model, MITgcm, to simulate water circulation driven by subglacial discharge at the terminus of an idealized Tidewater Glacier. We vary the spatial distribution of subglacial discharge emerging at the grounding line of the Glacier and examine the effect on submarine melt volume and distribution. We find that subglacial hydrology exerts an important control on submarine melting; under certain conditions a distributed system can induce a factor 5 more melt than a channelized system, with plumes from a single channel inducing melt over only a localized area. Subglacial hydrology also controls the spatial distribution of melt, which has the potential to control terminus morphology and calving style. Our results highlight the need to constrain near-terminus subglacial hydrology at Tidewater Glaciers if we are to represent ocean forcing accurately.
