Inter-annual variability in supraglacial lakes around East Antarctica

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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Distribution and seasonal evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

10.5194/tc-2020-101 ◽

2020 ◽

Author(s):

Jennifer F. Arthur ◽

Chris R. Stokes ◽

Stewart S. R. Jamieson ◽

J. Rachel Carr ◽

Amber A. Leeson

Keyword(s):

Climate Model ◽

Regional Climate ◽

East Antarctica ◽

Katabatic Wind ◽

Ice Shelf ◽

Ice Shelves ◽

Shelf Stability ◽

Seasonal Evolution ◽

Supraglacial Lakes ◽

Area And Volume

Abstract. Supraglacial lakes (SGLs) enhance surface melting and can flex and fracture ice shelves when they grow and subsequently drain, potentially leading to ice shelf disintegration. However, the seasonal evolution of SGLs and their influence on ice shelf stability in East Antarctica remains poorly understood, despite some potentially vulnerable ice shelves having high densities of SGLs. Using optical satellite imagery, air temperature data from climate reanalysis products and surface melt predicted by a regional climate model, we present the first long-term record (2000–2020) of seasonal SGL evolution on Shackleton Ice Shelf, which is Antarctica’s northernmost remaining ice shelf and buttresses Denman Glacier, a major outlet of the East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs with a mean area of 0.02 km2, a mean depth of 0.96 m, and a mean total meltwater volume of 7.45 x 106 m3. At their most extensive, SGLs cover a cumulative area of 50.7 km2 and are clustered near to the grounding line, where densities approach 0.27 km2 per km2. Here, SGL development is linked to an albedo-lowering feedback associated with katabatic winds, together with the presence of blue ice and exposed rock. Although below average seasonal (December-January-February, DJF) temperatures are associated with below average peaks in total SGL area and volume, warmer seasonal temperatures do not necessarily result in higher SGL areas and volumes. Rather, peaks in total SGL area and volume show a much closer correspondence with short-lived high magnitude snowmelt events. We therefore suggest seasonal lake evolution on this ice shelf is instead more sensitive to snowmelt intensity associated with katabatic wind-driven melting. Our analysis provides important constraints on the boundary conditions of supraglacial hydrology models and numerical simulations of ice shelf stability.

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An assessment of basal melting parameterisations for Antarctic ice shelves

10.5194/egusphere-egu21-1367 ◽

2021 ◽

Author(s):

Clara Burgard ◽

Nicolas Jourdain

Keyword(s):

Climate Model ◽

Ice Sheet ◽

Coupled Model ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Global Sea Level ◽

Basal Melting ◽

The Antarctic

Ocean-induced melting at the base of ice shelves is one of the main drivers of the currently observed mass loss of the Antarctic Ice Sheet. A good understanding of the interaction between ice and ocean at the base of the ice shelves is therefore crucial to understand and project the Antarctic contribution to global sea-level rise.&#160;Due to the high difficulty to monitor these regions, our understanding of the processes at work beneath ice shelves is limited. Still, several parameterisations of varying complexity have been developed in past decades to describe the ocean-induced sub-shelf melting. These parameterisations can be implemented into standalone ice-sheet models, for example when conducting long-term projections forced with climate model output.An assessment of the performance of these parameterisations was conducted in an idealised setup (Favier et al, 2019). However, the application of the better-performing parameterisations in a more realistic setup (e.g. Jourdain et al., 2020) has shown that individual adjustments and corrections are needed for each ice shelf.In this study, we revisit the assessment of the parameterisations, this time in a more realistic setup than previous studies. To do so, we apply the different parameterisations on several ice shelves around Antarctica and compare the resulting melt rates to satellite and oceanographic estimates. Based on this comparison, we will refine the parameters and propose an approach to reduce uncertainties in long-term sub-shelf melting projections.References - Favier, L., Jourdain, N. C., Jenkins, A., Merino, N., Durand, G., Gagliardini, O., Gillet-Chaulet, F., and Mathiot, P.: Assessment of sub-shelf melting parameterisations using the ocean&#8211;ice-sheet coupled model NEMO(v3.6)&#8211;Elmer/Ice(v8.3) , Geosci. Model Dev., 12, 2255&#8211;2283, https://doi.org/10.5194/gmd-12-2255-2019, 2019.&#160; - Jourdain, N. C., Asay-Davis, X., Hattermann, T., Straneo, F., Seroussi, H., Little, C. M., and Nowicki, S.: A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections, The Cryosphere, 14, 3111&#8211;3134, https://doi.org/10.5194/tc-14-3111-2020, 2020.&#160;

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Distribution and seasonal evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

The Cryosphere ◽

10.5194/tc-14-4103-2020 ◽

2020 ◽

Vol 14 (11) ◽

pp. 4103-4120 ◽

Cited By ~ 1

Author(s):

Jennifer F. Arthur ◽

Chris R. Stokes ◽

Stewart S. R. Jamieson ◽

J. Rachel Carr ◽

Amber A. Leeson

Keyword(s):

Climate Model ◽

Regional Climate ◽

East Antarctica ◽

Katabatic Wind ◽

Ice Shelf ◽

Ice Shelves ◽

Shelf Stability ◽

Seasonal Evolution ◽

Supraglacial Lakes ◽

Area And Volume

Abstract. Supraglacial lakes (SGLs) enhance surface melting and can flex and fracture ice shelves when they grow and subsequently drain, potentially leading to ice shelf disintegration. However, the seasonal evolution of SGLs and their influence on ice shelf stability in East Antarctica remains poorly understood, despite some potentially vulnerable ice shelves having high densities of SGLs. Using optical satellite imagery, air temperature data from climate reanalysis products and surface melt predicted by a regional climate model, we present the first long-term record (2000–2020) of seasonal SGL evolution on Shackleton Ice Shelf, which is Antarctica's northernmost remaining ice shelf and buttresses Denman Glacier, a major outlet of the East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs with a mean area of 0.02 km2, a mean depth of 0.96 m and a mean total meltwater volume of 7.45×106 m3. At their most extensive, SGLs cover a cumulative area of 50.7 km2 and are clustered near to the grounding line, where densities approach 0.27 km2 km−2. Here, SGL development is linked to an albedo-lowering feedback associated with katabatic winds, together with the presence of blue ice and exposed rock. Although below-average seasonal (December–January–February, DJF) temperatures are associated with below-average peaks in total SGL area and volume, warmer seasonal temperatures do not necessarily result in higher SGL areas and volumes. Rather, peaks in total SGL area and volume show a much closer correspondence with short-lived high-magnitude snowmelt events. We therefore suggest seasonal lake evolution on this ice shelf is instead more sensitive to snowmelt intensity associated with katabatic-wind-driven melting. Our analysis provides important constraints on the boundary conditions of supraglacial hydrology models and numerical simulations of ice shelf stability.

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Widespread distribution of supraglacial lakes around the margin of the East Antarctic Ice Sheet

Scientific Reports ◽

10.1038/s41598-019-50343-5 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 12

Author(s):

Chris R. Stokes ◽

Jack E. Sanderson ◽

Bertie W. J. Miles ◽

Stewart S. R. Jamieson ◽

Amber A. Leeson

Keyword(s):

Ice Sheet ◽

Ice Shelf ◽

Typically Develop ◽

Ice Shelves ◽

Supraglacial Lakes ◽

Marginal Areas ◽

Surface Slopes ◽

Highly Sensitive ◽

Ice Sheet Mass Balance ◽

High Resolution Satellite Imagery

Abstract Supraglacial lakes are important to ice sheet mass balance because their development and drainage has been linked to changes in ice flow velocity and ice shelf disintegration. However, little is known about their distribution on the world’s largest ice sheet in East Antarctica. Here, we use ~5 million km2 of high-resolution satellite imagery to identify >65,000 lakes (>1,300 km2) that formed around the peak of the melt season in January 2017. Lakes occur in most marginal areas where they typically develop at low elevations (<100 m) and on low surface slopes (<1°), but they can exist 500 km inland and at elevations >1500 m. We find that lakes often cluster a few kilometres down-ice from grounding lines and ~60% (>80% by area) develop on ice shelves, including some potentially vulnerable to collapse driven by lake-induced hydro-fracturing. This suggests that parts of the ice sheet may be highly sensitive to climate warming.

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Antarctic Supraglacial Lake Identification Using Landsat-8 Image Classification

Remote Sensing ◽

10.3390/rs12081327 ◽

2020 ◽

Vol 12 (8) ◽

pp. 1327 ◽

Cited By ~ 1

Author(s):

Anna Ruth W. Halberstadt ◽

Colin J. Gleason ◽

Mahsa S. Moussavi ◽

Allen Pope ◽

Luke D. Trusel ◽

...

Keyword(s):

Large Scale ◽

Seasonal Pattern ◽

Ice Sheet ◽

Training Data ◽

Landsat 8 ◽

Ice Shelf ◽

Ice Shelves ◽

Continental Scale ◽

Lake Evolution ◽

Supervised Classifiers

Surface meltwater generated on ice shelves fringing the Antarctic Ice Sheet can drive ice-shelf collapse, leading to ice sheet mass loss and contributing to global sea level rise. A quantitative assessment of supraglacial lake evolution is required to understand the influence of Antarctic surface meltwater on ice-sheet and ice-shelf stability. Cloud computing platforms have made the required remote sensing analysis computationally trivial, yet a careful evaluation of image processing techniques for pan-Antarctic lake mapping has yet to be performed. This work paves the way for automating lake identification at a continental scale throughout the satellite observational record via a thorough methodological analysis. We deploy a suite of different trained supervised classifiers to map and quantify supraglacial lake areas from multispectral Landsat-8 scenes, using training data generated via manual interpretation of the results from k-means clustering. Best results are obtained using training datasets that comprise spectrally diverse unsupervised clusters from multiple regions and that include rock and cloud shadow classes. We successfully apply our trained supervised classifiers across two ice shelves with different supraglacial lake characteristics above a threshold sun elevation of 20°, achieving classification accuracies of over 90% when compared to manually generated validation datasets. The application of our trained classifiers produces a seasonal pattern of lake evolution. Cloud shadowed areas hinder large-scale application of our classifiers, as in previous work. Our results show that caution is required before deploying ‘off the shelf’ algorithms for lake mapping in Antarctica, and suggest that careful scrutiny of training data and desired output classes is essential for accurate results. Our supervised classification technique provides an alternative and independent method of lake identification to inform the development of a continent-wide supraglacial lake mapping product.

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Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation

10.5194/egusphere-egu2020-7801 ◽

2020 ◽

Author(s):

Frazer Christie ◽

Toby Benham ◽

Julian Dowdeswell

Keyword(s):

Sea Ice ◽

Antarctic Peninsula ◽

Ice Sheet ◽

Weddell Sea ◽

Landsat 8 ◽

Ice Shelf ◽

Total Contribution ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

The Antarctic

The Antarctic Peninsula is one of the most rapidly warming regions on Earth. There, the recent destabilization of the Larsen A and B ice shelves has been directly attributed to this warming, in concert with anomalous changes in ocean circulation. Having rapidly accelerated and retreated following the demise of Larsen A and B, the inland glaciers once feeding these ice shelves now form a significant proportion of Antarctica&#8217;s total contribution to global sea-level rise, and have become an exemplar for the fate of the wider Antarctic Ice Sheet under a changing climate. Together with other indicators of glaciological instability observable from satellites, abrupt pre-collapse changes in ice shelf terminus position are believed to have presaged the imminent disintegration of Larsen A and B, which necessitates the need for routine, close observation of this sector in order to accurately forecast the future stability of the Antarctic Peninsula Ice Sheet. To date, however, detailed records of ice terminus position along this region of Antarctica only span the observational period c.1950 to 2008, despite several significant changes to the coastline over the last decade, including the calving of giant iceberg A-68a from Larsen C Ice Shelf in 2017.Here, we present high-resolution, annual records of ice terminus change along the entire western Weddell Sea Sector, extending southwards from the former Larsen A Ice Shelf on the eastern Antarctic Peninsula to the periphery of Filchner Ice Shelf. Terminus positions were recovered primarily from Sentinel-1a/b, TerraSAR-X and ALOS-PALSAR SAR imagery acquired over the period 2009-2019, and were supplemented with Sentinel-2a/b, Landsat 7 ETM+ and Landsat 8 OLI optical imagery across regions of complex terrain.Confounding Antarctic Ice Sheet-wide trends of increased glacial recession and mass loss over the long-term satellite era, we detect glaciological advance along 83% of the ice shelves fringing the eastern Antarctic Peninsula between 2009 and 2019. With the exception of SCAR Inlet, where the advance of its terminus position is attributable to long-lasting ice dynamical processes following the disintegration of Larsen B, this phenomenon lies in close agreement with recent observations of unchanged or arrested rates of ice flow and thinning along the coastline. Global climate reanalysis and satellite passive-microwave records reveal that this spatially homogenous advance can be attributed to an enhanced buttressing effect imparted on the eastern Antarctic Peninsula&#8217;s ice shelves, governed primarily by regional-scale increases in the delivery and concentration of sea ice proximal to the coastline.

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The Atmospheric River Threat to Antarctic Peninsula Ice-Shelf Stability

10.21203/rs.3.rs-828007/v1 ◽

2021 ◽

Author(s):

Jonathan Wille ◽

Vincent Favier ◽

Nicolas Jourdain ◽

Christoph Kittel ◽

Jenny Turton ◽

...

Keyword(s):

Antarctic Peninsula ◽

Climate Model ◽

Regional Climate ◽

Detection Algorithm ◽

Ice Shelf ◽

Ice Shelves ◽

Atmospheric River ◽

The Antarctic ◽

Collapse Theories ◽

Temperature Surface

Abstract The disintegration of the ice shelves along the Antarctic Peninsula have spurred much discussion on the various processes leading to their eventual dramatic collapse, but without a consensus on an atmospheric forcing that could connect these processes. Here, using an atmospheric river (AR) detection algorithm along with a regional climate model and satellite observations, we show that particularly intense ARs have a ~40% probability of inducing extreme events of temperature, surface melt, sea-ice disintegration, or large swells; all processes proven to induce ice-shelf destabilization. This was observed during the collapses of the Larsen A, B, and overall, 60% of calving events triggered by ARs from 2000-2020. The loss of the buttressing effect from these ice shelves leads to further continental ice loss and subsequent sea-level rise. Understanding how ARs connect various disparate processes cited in ice-shelf collapse theories is essential for identifying other at-risk ice shelves like the Larsen C.

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Seasonal evolution of Antarctic supraglacial lakes in 2015–2021 and links to environmental controls

10.5194/tc-2021-203 ◽

2021 ◽

Author(s):

Mariel Christina Dirscherl ◽

Andreas J. Dietz ◽

Claudia Kuenzer

Keyword(s):

Antarctic Peninsula ◽

Time Lags ◽

Ice Shelf ◽

Ice Shelves ◽

Shelf Stability ◽

Air Content ◽

Supraglacial Lakes ◽

Environmental Controls ◽

Lake Formation ◽

Increased Risk

Abstract. Supraglacial meltwater accumulation on ice shelves may have important implications for future sea-level-rise. Despite recent progress in the understanding of Antarctic surface hydrology, potential influences on ice shelf stability as well as links to environmental drivers remain poorly constrained. In this study, we employ state-of-the-art machine learning on Sentinel-1 Synthetic Aperture Radar (SAR) and optical Sentinel-2 satellite imagery to provide new insight into the inter-annual and intra-annual evolution of surface hydrological features across six major Antarctic Peninsula and East Antarctic ice shelves. For the first time, we produce a record of supraglacial lake extent dynamics for the period 2015–2021 at unprecedented 10 m spatial resolution and bi-weekly temporal scale. Through synergetic use of optical and SAR data, we obtain a more complete mapping record enabling the delineation of also buried lakes. Our results for Antarctic Peninsula ice shelves reveal below average meltwater ponding during most of melting seasons 2015–2018 and above average meltwater ponding throughout summer 2019–2020 and early 2020–2021. Meltwater ponding on investigated East Antarctic ice shelves was far more variable with above average lake extents during most of melting seasons 2016–2019 and below average lake extents during 2020–2021. This study is the first to investigate relationships with climate drivers both, spatially and temporally including time lag analysis. The results indicate that supraglacial lake formation in 2015–2021 is coupled to the complex interplay of varying air temperature, solar radiation, snowmelt, wind and precipitation, each at different time lags and directions and with strong local to regional discrepancies, as revealed through pixel-based correlation analysis. Southern Hemisphere atmospheric modes as well as the local glaciological setting including melt-albedo feedbacks and the firn air content were revealed to strongly influence the spatio-temporal evolution of supraglacial lakes as well as below or above average meltwater ponding despite variations in the strength of forcing. Recent increases of Antarctic Peninsula surface ponding point towards a further reduction of the firn air content implying an increased risk for ponding and hydrofracture. In addition, lateral meltwater transport was observed over both Antarctic regions with similar implications for future ice shelf stability.

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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 role of ocean circulation in the propagation of rifts on ice shelves.

10.5194/egusphere-egu2020-10919 ◽

2020 ◽

Author(s):

Mattia Poinelli ◽

Eric Larour ◽

Riccardo Riva

Keyword(s):

Ocean Circulation ◽

Regional Climate ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Ice Shelves ◽

Rift Propagation ◽

Break Up ◽

The Stability

The break-up of large ice shelves and the associated loss of ice are thought to play a destabilizing role in the ice sheet dynamics.&#160;Although ice shelves are a substantial buttressing source in the stability of continental ice sheets, the propagation of large rifts eventually leads to the break-up of icebergs into the ocean.&#160;As consequence, this loss of ice would trigger further glacier acceleration and ice sheets retreat, destabilizing the ice cap.&#160;Retreat and collapse of ice sheets are also thought to be related to regional climate warming.&#160;Indeed, satellite observations suggest that a warming surrounding would induce the ice sheet to progressive thinning and weakening.The prolongation of un-grounded ice into the ocean is often interrupted by the propagation of fractures that eventually separates large icebergs from the ice shelf.&#160;These fractures are called rifts and range from dimensions of 10 to 100 km.&#160;A recent example of such phenomena is the massive break-up of the Larsen C in July, 2017 which followed the disintegration of Larsen A in 1995 and the partial break-up of Larsen B in 2002.&#160;The tabular iceberg formed by Larsen C was limited by the propagation of a large rift that began in summer 2016, although the ice shelf had already been thinning since 1992.Rift initiation and propagation are thought to be the result of glaciological and oceanographic sources that trigger ice to break.&#160;Nonetheless, exact mechanisms remain elusive.&#160;The on-going project focuses on ice-ocean interactions in ice shelves that accommodate rifts by using oceanographic models.&#160;The goal is to couple rift propagation and ocean circulation underneath ice cavities in order to infer how basal melting affects the development of rifts.&#160;The numerical framework is developed within the capabilities of the MITgcm.&#160;We aim to identify the sensitivity of propagation rate and opening rate of rifts to variations in the ocean circulation that have occurred during the separation of part of the ice shelf.On a larger scale, we are interested in the role of rifting in the stability of Antarctic shelves.&#160;Therefore, we work toward a better understanding of which processes are involved in the triggering of rift propagation.

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