32-year record-high surface melt in 2019/2020 on north George VI Ice Shelf, Antarctic Peninsula

Abstract. In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of dramatically lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer (and scatterometer) data, which are sensitive to meltwater on the ice-shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (since 2013) and Sentinel-2 (since 2017), record volumes of surface meltwater ponding are also observed on north GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of meltwater on January 19. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ≥ 0 °C for anomalously long periods (55–90 hours) from late November onwards, likely driven by warmer northwesterly and northeasterly low-speed winds. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting.

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The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula

The Cryosphere ◽

10.5194/tc-15-909-2021 ◽

2021 ◽

Vol 15 (2) ◽

pp. 909-925

Author(s):

Alison F. Banwell ◽

Rajashree Tri Datta ◽

Rebecca L. Dell ◽

Mahsa Moussavi ◽

Ludovic Brucker ◽

...

Keyword(s):

High Surface ◽

Microwave Radiometer ◽

Austral Summer ◽

Landsat 8 ◽

Ice Shelf ◽

Near Surface ◽

Ice Shelves ◽

Air Content ◽

Air Temperatures ◽

Surface Melt

Abstract. In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of distinctly lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer and scatterometer data, which are sensitive to meltwater on the ice shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (2013 to 2020) and Sentinel-2 (2017 to 2020), record volumes of surface meltwater ponding were also observed on the northern GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of ponded meltwater on 19 January. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ≥0 ∘C for anomalously long periods (55 to 90 h) from late November onwards, which limited meltwater refreezing. The sustained warm periods were likely driven by warm, low-speed (≤7.5 m s−1) northwesterly and northeasterly winds and not by foehn wind conditions, which were only present for 9 h total in the 2019/2020 melt season. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting.

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The 2020 Larsen C Ice Shelf surface melt is a 40-year record high

The Cryosphere ◽

10.5194/tc-14-3551-2020 ◽

2020 ◽

Vol 14 (10) ◽

pp. 3551-3564

Author(s):

Suzanne Bevan ◽

Adrian Luckman ◽

Harry Hendon ◽

Guomin Wang

Keyword(s):

Southern Hemisphere ◽

Antarctic Peninsula ◽

Austral Summer ◽

Ice Shelf ◽

Atmospheric Flow ◽

Air Content ◽

Positive Indian Ocean Dipole ◽

Air Temperatures ◽

The Tropics ◽

The Antarctic

Abstract. Along with record-breaking summer air temperatures at an Antarctic Peninsula meteorological station in February 2020, the Larsen C ice shelf experienced an exceptionally long and extensive 2019/2020 melt season. We use a 40-year time series of passive and scatterometer satellite microwave data, which are sensitive to the presence of liquid water in the snow pack, to reveal that the extent and duration of melt observed on the ice shelf in the austral summer of 2019/2020 was the greatest on record. We find that unusual perturbations to Southern Hemisphere modes of atmospheric flow, including a persistently positive Indian Ocean Dipole in the spring and a very rare Southern Hemisphere sudden stratospheric warming in September 2019, preceded the exceptionally warm Antarctic Peninsula summer. It is likely that teleconnections between the tropics and southern high latitudes were able to bring sufficient heat via the atmosphere and ocean to the Antarctic Peninsula to drive the extreme Larsen C Ice Shelf melt. The record-breaking melt of 2019/2020 brought to an end the trend of decreasing melt that had begun in 1999/2000, will reinitiate earlier thinning of the ice shelf by depletion of the firn air content, and probably affected a much greater region than Larsen C Ice Shelf.

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Supervised classification of slush and ponded water on Antarctic ice shelves using Landsat 8 imagery

Journal of Glaciology ◽

10.1017/jog.2021.114 ◽

2021 ◽

pp. 1-14

Author(s):

Rebecca L. Dell ◽

Alison F. Banwell ◽

Ian C. Willis ◽

Neil S. Arnold ◽

Anna Ruth W. Halberstadt ◽

...

Keyword(s):

Supervised Classification ◽

Clustering Algorithm ◽

Google Earth ◽

Expert Elicitation ◽

Future Research ◽

Landsat 8 ◽

Ice Shelf ◽

Ice Shelves ◽

Air Content

Abstract Surface meltwater is becoming increasingly widespread on Antarctic ice shelves. It is stored within surface ponds and streams, or within firn pore spaces, which may saturate to form slush. Slush can reduce firn air content, increasing an ice-shelf's vulnerability to break-up. To date, no study has mapped the changing extent of slush across ice shelves. Here, we use Google Earth Engine and Landsat 8 images from six ice shelves to generate training classes using a k-means clustering algorithm, which are used to train a random forest classifier to identify both slush and ponded water. Validation using expert elicitation gives accuracies of 84% and 82% for the ponded water and slush classes, respectively. Errors result from subjectivity in identifying the ponded water/slush boundary, and from inclusion of cloud and shadows. We apply our classifier to the Roi Baudouin Ice Shelf for the entire 2013–20 Landsat 8 record. On average, 64% of all surface meltwater is classified as slush and 36% as ponded water. Total meltwater areal extent is greatest between late January and mid-February. This highlights the importance of mapping slush when studying surface meltwater on ice shelves. Future research will apply the classifier across all Antarctic ice shelves.

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A record of slush and water extent on Antarctic ice shelves from 2013 to present day

10.5194/egusphere-egu21-16349 ◽

2021 ◽

Author(s):

Rebecca Dell ◽

Alison Banwell ◽

Neil Arnold ◽

Ian Willis ◽

Anna Ruth W. Halberstadt ◽

...

Keyword(s):

Clustering Algorithm ◽

Google Earth ◽

Expert Elicitation ◽

Water Bodies ◽

Landsat 8 ◽

Ice Shelf ◽

Ice Shelves ◽

Air Temperatures ◽

Run Off ◽

Shelf Dynamics

Supraglacial melt is observed across the majority of Antarctic ice shelves and is expected to increase in line with rising air temperatures. Surface meltwater may run off the ice shelf edge and into the ocean, or be stored within firn pore spaces (slush) and supraglacial water bodies (ponds, lakes or streams). When stored either as slush or supraglacial water bodies, the water can indirectly impact ice shelf dynamics, and potentially facilitate ice shelf collapse. Numerous studies have quantified ice shelf meltwater in supraglacial water bodies, however, despite its importance, no studies exist that quantify the extent of slush on a pan-Antarctic scale.Here, we develop a supervised classifier in Google Earth Engine capable of identifying both slush and ponded water on a pan-Antarctic scale using Landsat 8 imagery. We train and test our classifier on six ice shelves: (1) Nivlisen, (2) Roi Baudouin, (3) Amery, (4) Shackleton, (5) Nansen, (6) George VI. A k-means clustering algorithm is applied to selected Landsat 8 training scenes, and the output clusters are manually interpreted to form training classes (i.e. slush, water, and other surface types (e.g.&#160;blue ice, dirty ice)). These training classes are then used to train a Random Forest Classifier, and the accuracy of the outputs are assessed using expert elicitation. Overall, the classifier accuracy for water and slush is 78 % and 70 % respectively. The validated classifier is then applied to numerous ice shelves across Antarctica, in order to produce estimates of slush and water extent from 2013 to the present day.

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Evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

10.5194/egusphere-egu2020-1427 ◽

2020 ◽

Author(s):

Jennifer Arthur ◽

Chris Stokes ◽

Stewart Jamieson ◽

Rachel Carr ◽

Amber Leeson

Keyword(s):

Climate Model ◽

High Surface ◽

Surface Melting ◽

East Antarctica ◽

Ice Shelf ◽

Ice Shelves ◽

Shelf Stability ◽

Supraglacial Lakes ◽

Surface Melt ◽

The Impact

Supraglacial lakes (SGLs) enhance surface melting and their development and subsequent drainage can flex and fracture ice shelves, leading to their disintegration. However, the seasonal evolution of SGLs and their potential influence on ice shelf stability in East Antarctica remains poorly understood, despite a number of potentially vulnerable ice shelves. Using optical satellite imagery, climate reanalysis data and surface melt predicted by a regional climate model, we provide the first multi-year analysis (1974-2019) of seasonal SGL evolution on Shackleton Ice Shelf in Queen Mary Land, which is Antarctica&#8217;s northernmost remaining ice shelf. We mapped >43,000 lakes on the ice shelf and >5,000 lakes on grounded ice over the 45-year analysis period, some of which developed up to 12 km inland from the grounding line. Lakes clustered around the ice shelf grounding zone are strongly linked to the presence of blue ice and exposed rock, associated with an albedo-lowering melt-enhancing feedback. Lakes either drain supraglacially, refreeze at the end of the melt season, or shrink in-situ. Furthermore, we observe some relatively rapid (&#8804; 7 days) lake drainage events and infer that some lakes may be draining by hydrofracture. Our observations suggest that enhanced surface meltwater could increase the vulnerability of East Antarctic ice shelves already preconditioned for hydrofracture, namely those experiencing high surface melt rates, firn air depletion, and extensional stress regimes with minimum topographic confinement. Our results could be used to constrain simulations of current melt conditions on the ice shelf and to investigate the impact of increased surface melting on future ice shelf stability.

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2020 Larsen C Ice Shelf surface melt is a 40-year record high

10.5194/tc-2020-130 ◽

2020 ◽

Author(s):

Suzanne Bevan ◽

Adrian Luckman ◽

Harry Hendon ◽

Guomin Wang

Keyword(s):

Southern Hemisphere ◽

Antarctic Peninsula ◽

Austral Summer ◽

Ice Shelf ◽

Atmospheric Flow ◽

Air Content ◽

Positive Indian Ocean Dipole ◽

Air Temperatures ◽

The Tropics ◽

The Antarctic

Abstract. Along with record-breaking summer air temperatures at two Antarctic Peninsula meteorological stations in February 2020, the Larsen C ice shelf experienced an exceptionally long and extensive 2019/2020 melt season. We use a 40-year time series of passive and scatterometer satellite microwave data, which is sensitive to the presence of liquid water in the snow pack, to reveal that the extent and duration of melt observed on the ice shelf in the austral summer of 2019/2020 was the greatest on record. We find that unusual perturbations to southern hemisphere modes of atmospheric flow, including a persistently positive Indian Ocean Dipole in the spring and a very rare southern hemisphere sudden stratospheric warming in September 2019, preceded the exceptionally warm Antarctic Peninsula summer. It is likely that tele-connections between the tropics and southern high latitudes were able to bring sufficient heat via the atmosphere and ocean to the Antarctic Peninsula to drive the extreme Larsen C Ice Shelf melt. The record breaking melt of 2019/2020 brought to an end the trend of decreasing melt that had begun in 1999/2000, and will re-initiate earlier thinning of the ice shelf by depletion of the firn air content.

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Inter-annual variability in supraglacial lakes around East Antarctica

10.5194/egusphere-egu21-6263 ◽

2021 ◽

Author(s):

Jennifer Arthur ◽

Chris Stokes ◽

Stewart Jamieson ◽

Rachel Carr ◽

Amber Leeson

Keyword(s):

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Landsat 8 ◽

Ice Shelf ◽

Ice Shelves ◽

Flow Acceleration ◽

Air Content ◽

Supraglacial Lakes ◽

Global Sea Level

Surface meltwater ponding can weaken and trigger the rapid disintegration of Antarctic ice shelves which buttress the ice sheet, causing ice flow acceleration and global sea-level rise. While supraglacial lakes (SGLs) are relatively well documented during some years and selected ice shelves in Antarctica, we have little understanding of how Antarctic-wide SGL coverage varies between melt seasons. Here, we present a record of SGL evolution around the peak of the melt season on the East Antarctic Ice Sheet (EAIS) over seven consecutive years. Our findings are based on a threshold-based algorithm applied to 2175 Landsat 8 images during the month of January from 2014 to 2020. We find that EAIS-wide SGL volume fluctuates inter-annually by up to ~80%. Moreover, patterns within regions and on neighbouring ice shelves are not necessarily synchronous. Over the whole EAIS, total SGL volume was greatest in January 2017, dominated by the Amery and Roi Baudouin ice shelves, and lowest in January 2016. Excluding these two ice shelves, SGL volume peaked in January 2020. Preliminary results suggest EAIS-wide total SGL volume and extent are weakly correlated with firn model simulations of firn air content, surface melt and minimum ice lens depth predicted by the regional climate model MAR. On certain ice shelves, years with peak SGL volume correspond with minimum firn air content. This work provides important constraints for numerical ice-shelf and ice-sheet model predictions of future Antarctic surface meltwater distributions and the potential impact on ice-sheet stability and flow. &#160;

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Surface lake depths on an Antarctic ice shelf: comparing in-situ measurements with ground and satellite multispectral methods

10.5194/egusphere-egu2020-10677 ◽

2020 ◽

Author(s):

Ian Willis ◽

Alison Banwell ◽

Grant Macdonald ◽

Michael Willis ◽

Doug MacAyeal

Keyword(s):

Light Attenuation ◽

Ice Sheet ◽

Austral Summer ◽

Greenland Ice Sheet ◽

Water Bodies ◽

Subsurface Water ◽

Landsat 8 ◽

Ice Shelf ◽

Ice Shelves ◽

Water Volumes

There is growing interest in surface and shallow subsurface water bodies across Antarctic ice shelves as they impact the ice shelf mass balance. Additionally, the filling and draining of lakes has the potential to flex and fracture ice shelves, which may even lead to their catastrophic break up. The study of lakes on ice shelf surfaces typically uses optical satellite imagery to delineate their area and a parameterised physically-based light attenuation theory to calculate their depths. The approach has been developed and validated using various data sets collected on the Greenland Ice Sheet, but so far the approach has not been validated for Antarctic ice shelves. Here we use simultaneous field measurements of lake water depth and surface spectral properties (red, blue, green, panchromatic), to parameterise the light attenuation theory for use during the filling and draining of shallow lakes on the McMurdo Ice Shelf during the 2016/2017 austral summer. We then apply the approach to calculate lake areas, depths and volumes across several water bodies observed in high resolution Worldview imagery, which helps validate the approach to calculating water volumes across a larger part of the ice shelf using Landsat 8 imagery. Results suggest that using parameter values relevant to the Greenland Ice Sheet may bias the calculation of water volumes when applied to Antarctic ice shelves, and we suggest more appropriate values.

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Surface mass balance and melting projections over the Amundsen coastal region, West Antarctica

10.5194/egusphere-egu2020-16488 ◽

2020 ◽

Author(s):

Nicolas Jourdain ◽

Marion Donat-Magnin ◽

Christoph Kittel ◽

Cécile Agosta ◽

Charles Amory ◽

...

Keyword(s):

Mass Balance ◽

Projection Method ◽

Surface Mass Balance ◽

West Antarctica ◽

Ice Shelf ◽

Near Surface ◽

Surface Mass ◽

Ice Shelves ◽

The Future ◽

Surface Melt

We present Surface Mass Balance (SMB) and surface melt rates projections in West Antarctica for the end of the 21st century using the MAR regional atmosphere and firn model (Gall&#233;e 1994; Agosta et al. 2019) forced by a CMIP5-rcp85 multi-model-mean seasonal anomaly added to the ERA-Interim 6-hourly reanalysis.&#160;First of all, we assess the validity of our projection method, following a perfect-model approach, with MAR constrained by the ACCESS-1.3 present-day and future climates. Changes in large-scale variables are well captured by our anomaly-based projection method, and errors on surface melting and SMB projections are typically 10%.&#160;Based on the CMIP5-rcp85 multi-model mean, SMB over the grounded ice sheet in the Amundsen sector is projected to increase by 35% over the 21st century. This corresponds to a SMB sensitivity to near-surface warming of 8.3%.&#176;C-1. Increased humidity, resulting from both higher water vapour saturation in warmer conditions and decreased sea-ice concentrations, are shown to favour increased SMB in the future scenario.&#160;Ice-shelf surface melt rates at the end of the 21st century are projected to become 6 to 15 times larger than presently, depending on the ice shelf under consideration. This is due to enhanced downward longwave radiative fluxes related to increased humidity, and to an albedo feedback leading to more absorption of shortwave radiation. Interestingly, only three ice shelves produce runoff (Abbot, Cosgrove and Pine Island) in the future climate. For the other ice shelves (Thwaites, Crosson, Dotson, Getz), the future melt-to-snowfall ratio remains too low to produce firn air depletion and subsequent runoff.&#160;

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Greenland climate simulations show high Eemian surface melt which could explain reduced total air content in ice cores

Climate of the Past ◽

10.5194/cp-17-317-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 317-330

Author(s):

Andreas Plach ◽

Bo M. Vinther ◽

Kerim H. Nisancioglu ◽

Sindhu Vudayagiri ◽

Thomas Blunier

Keyword(s):

High Surface ◽

Ice Core ◽

Ice Cores ◽

Surface Elevation ◽

Balance Model ◽

Interglacial Period ◽

Air Content ◽

Climate Simulations ◽

Surface Melt ◽

Eemian Interglacial

Abstract. This study presents simulations of Greenland surface melt for the Eemian interglacial period (∼130 000 to 115 000 years ago) derived from regional climate simulations with a coupled surface energy balance model. Surface melt is of high relevance due to its potential effect on ice core observations, e.g., lowering the preserved total air content (TAC) used to infer past surface elevation. An investigation of surface melt is particularly interesting for warm periods with high surface melt, such as the Eemian interglacial period. Furthermore, Eemian ice is the deepest and most compressed ice preserved on Greenland, resulting in our inability to identify melt layers visually. Therefore, simulating Eemian melt rates and associated melt layers is beneficial to improve the reconstruction of past surface elevation. Estimated TAC, based on simulated melt during the Eemian, could explain the lower TAC observations. The simulations show Eemian surface melt at all deep Greenland ice core locations and an average of up to ∼30 melt days per year at Dye-3, corresponding to more than 600 mm water equivalent (w.e.) of annual melt. For higher ice sheet locations, between 60 and 150 mmw.e.yr-1 on average are simulated. At the summit of Greenland, this yields a refreezing ratio of more than 25 % of the annual accumulation. As a consequence, high melt rates during warm periods should be considered when interpreting Greenland TAC fluctuations as surface elevation changes. In addition to estimating the influence of melt on past TAC in ice cores, the simulated surface melt could potentially be used to identify coring locations where Greenland ice is best preserved.

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