scholarly journals Advances in modelling subglacial lakes and their interaction with the Antarctic ice sheet

2016 ◽  
Vol 374 (2059) ◽  
pp. 20140296 ◽  
Author(s):  
Frank Pattyn ◽  
Sasha P. Carter ◽  
Malte Thoma
Keyword(s):  
Water Discharge ◽  
Ice Sheet ◽  
Point Of View ◽  
Transport Modelling ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Complex Interactions ◽  
Subglacial Lakes ◽  
Short Time ◽  
The Antarctic

Subglacial lakes have long been considered hydraulically isolated water bodies underneath ice sheets. This view changed radically with the advent of repeat-pass satellite altimetry and the discovery of multiple lake discharges and water infill, associated with water transfer over distances of more than 200 km. The presence of subglacial lakes also influences ice dynamics, leading to glacier acceleration. Furthermore, subglacial melting under the Antarctic ice sheet is more widespread than previously thought, and subglacial melt rates may explain the availability for water storage in subglacial lakes and water transport. Modelling of subglacial water discharge in subglacial lakes essentially follows hydraulics of subglacial channels on a hard bed, where ice sheet surface slope is a major control on triggering subglacial lake discharge. Recent evidence also points to the development of channels in deformable sediment in West Antarctica, with significant water exchanges between till and ice. Most active lakes drain over short time scales and respond rapidly to upstream variations. Several Antarctic subglacial lakes exhibit complex interactions with the ice sheet due to water circulation. Subglacial lakes can therefore—from a modelling point of view—be seen as confined small oceans underneath an imbedded ice shelf.

Automated mapping of Antarctic supraglacial lakes and streams using machine learning

2020 ◽  
Author(s):  
Mariel Dirscherl ◽  
Andreas Dietz ◽  
Celia Baumhoer ◽  
Christof Kneisel ◽  
Claudia Kuenzer
Keyword(s):  
Machine Learning ◽  
Mass Balance ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Supraglacial Lakes ◽  
The Antarctic ◽  
Sentinel 2

<p>Antarctica stores ~91 % of the global ice mass making it the biggest potential contributor to global sea-level-rise. With increased surface air temperatures during austral summer as well as in consequence of global climate change, the ice sheet is subject to surface melting resulting in the formation of supraglacial lakes in local surface depressions. Supraglacial meltwater features may impact Antarctic ice dynamics and mass balance through three main processes. First of all, it may cause enhanced ice thinning thus a potentially negative Antarctic Surface Mass Balance (SMB). Second, the temporary injection of meltwater to the glacier bed may cause transient ice speed accelerations and increased ice discharge. The last mechanism involves a process called hydrofracturing i.e. meltwater-induced ice shelf collapse caused by the downward propagation of surface meltwater into crevasses or fractures, as observed along large coastal sections of the northern Antarctic Peninsula. Despite the known impact of supraglacial meltwater features on ice dynamics and mass balance, the Antarctic surface hydrological network remains largely understudied with an automated method for supraglacial lake and stream detection still missing. Spaceborne remote sensing and data of the Sentinel missions in particular provide an excellent basis for the monitoring of the Antarctic surface hydrological network at unprecedented spatial and temporal coverage.</p><p>In this study, we employ state-of-the-art machine learning for automated supraglacial lake and stream mapping on basis of optical Sentinel-2 satellite data. With more detail, we use a total of 72 Sentinel-2 acquisitions distributed across the Antarctic Ice Sheet together with topographic information to train and test the selected machine learning algorithm. In general, our machine learning workflow is designed to discriminate between surface water, ice/snow, rock and shadow being further supported by several automated post-processing steps. In order to ensure the algorithm’s transferability in space and time, the acquisitions used for training the machine learning model are chosen to cover the full circle of the 2019 melt season and the data selected for testing the algorithm span the 2017 and 2018 melt seasons. Supraglacial lake predictions are presented for several regions of interest on the East and West Antarctic Ice Sheet as well as along the Antarctic Peninsula and are validated against randomly sampled points in the underlying Sentinel-2 RGB images. To highlight the performance of our model, we specifically focus on the example of the Amery Ice Shelf in East Antarctica, where we applied our algorithm on Sentinel-2 data in order to present the temporal evolution of maximum lake extent during three consecutive melt seasons (2017, 2018 and 2019).</p>

scholarly journals Changes in ice dynamics and mass balance of the Antarctic ice sheet

2006 ◽  
Vol 364 (1844) ◽  
pp. 1637-1655 ◽  
Author(s):  
Eric Rignot
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheet ◽  
East Antarctica ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
The Antarctic

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1 m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 °C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

scholarly journals Present-day high-resolution ice velocity map of the Antarctic ice sheet

2018 ◽  
Author(s):  
Qiang Shen ◽  
Hansheng Wang ◽  
C. K. Shum ◽  
Liming Jiang ◽  
Hou Tse Hsu ◽  
...  
Keyword(s):  
Sea Level ◽  
Displacement Vector ◽  
Ice Sheet ◽  
Landsat 8 ◽  
Ice Streams ◽  
Coupled Models ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Ice Velocity ◽  
The Antarctic

Abstract. Ice velocity constitutes a key parameter for estimating ice-sheet discharge rates and is crucial for improving coupled models of the Antarctic ice sheet to accurately predict its future fate and contribution to sea-level change. Here, we present a new Antarctic ice velocity map at a 100-m grid spacing inferred from Landsat 8 imagery data collected from December 2013 through March 2016 and robustly processed using the feature tracking method. These maps were assembled from over 73,000 displacement vector scenes inferred from over 32,800 optical images. Our maps cover nearly all the ice shelves, landfast ice, ice streams, and most of the ice sheet. The maps have an estimated uncertainty of less than 10 m yr-1 based on robust internal and external validations. These datasets will allow for a comprehensive continent-wide investigation of ice dynamics and mass balance combined with the existing and future ice velocity measurements and provide researchers access to better information for monitoring local changes in ice glaciers. Other uses of these datasets include control and calibration of ice-sheet modelling, developments in our understanding of Antarctic ice-sheet evolution, and improvements in the fidelity of projects investigating sea-level rise (https://doi.pangaea.de/10.1594/PANGAEA.895738).

Draining and Filling of an Interconnected Sub-glacial Lake Network in East Antarctica

2021 ◽  
Author(s):  
Anna Hogg ◽  
Noel Gourmelen ◽  
Richard Rigby ◽  
Thomas Slater
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
East Antarctica ◽  
Glacial Lake ◽  
Antarctic Ice Sheet ◽  
Geothermal Heating ◽  
Hydrological System ◽  
Subglacial Lakes ◽  
The Antarctic ◽  
The Impact

<p>The Antarctic Ice sheet is a key component of the Earth system, impacting on global sea level, ocean circulation and atmospheric processes. Meltwater is generated at the ice sheet base primarily by geothermal heating and friction associated with ice flow, and this feeds a vast network of lakes and rivers creating a unique hydrological environment. Subglacial lakes play a fundamental role in the Antarctic ice sheet hydrological system because outbursts from ‘active’ lakes can trigger, (i) change in ice speed, (ii) a burst of freshwater input into the ocean which generates buoyant meltwater plumes, and (iii) evolution of glacial landforms and sub-glacial habitats. Despite the key role that sub-glacial hydrology plays on the ice sheet environment, there are limited observations of repeat sub-glacial lake activity resulting in poor knowledge of the timing and frequency of these events. Even rarer are examples of interconnected lake activity, where the draining of one lake triggers filling of another. Observations of this nature help us better characterise these events and the impact they may have on Antarctica’s hydrological budget, and will advance our knowledge of the physical mechanism responsible for triggering this activity. In this study we analyse 9-years of CryoSat-2 radar altimetry data, to investigate a newly identified sub-glacial network in the Amery basin, East Antarctica. CryoSat-2 data was processed in ‘swath mode’, increasing the density of elevation measurements across the study area. The plane fit method was employed in 500 m by 500 m grid cells, to measure surface elevation change at relatively high spatial resolution. We identified a network of 10 active subglacial lakes in the Amery basin. 7 of these lakes, located below Lambert Glacier, show interconnected hydrological behaviour, with filling and drainage events throughout the study period. We observed ice surface height change of up to 6 meters on multiple lakes, and these observations were validated by independently acquired TanDEM-X DEM differencing. This case study is an important decade long record of hydrological activity beneath the Antarctic Ice Sheet which demonstrates the importance of high resolution swath mode measurements. In the future the Lambert lake network will be used to better understand the filling and draining life cycle of sub-glacial hydrological activity under the Antarctic Ice Sheet.</p><p></p>

scholarly journals Antarctic subglacial hydrology: current knowledge and future challenges

2014 ◽  
Vol 26 (6) ◽  
pp. 758-773 ◽  
Author(s):  
David W. Ashmore ◽  
Robert G. Bingham
Keyword(s):  
Current Knowledge ◽  
Ice Sheet ◽  
Dynamic Network ◽  
Antarctic Ice Sheet ◽  
Drainage Networks ◽  
Future Challenges ◽  
Nutrient Productivity ◽  
Subglacial Lakes ◽  
The Antarctic ◽  
Subglacial Drainage

AbstractFlood-carved landforms across the deglaciated terrain of Victoria Land, East Antarctica, provide convincing geomorphological evidence for the existence of subglacial drainage networks beneath the Antarctic ice sheet, and motivate research into the inaccessible environment beneath the contemporary ice sheet. Through this research, our understanding of Antarctic subglacial hydrology is steadily building, and this paper presents an overview of the current state of knowledge. The conceptualization of subglacial hydrological behaviour was developed at temperate and Arctic glaciers, and is thus less mature in the Antarctic. Geophysical and remote sensing observations have demonstrated that many subglacial lakes form part of a highly dynamic network of subglacial drainage beneath the Antarctic ice sheet. Recent research into subglacial water flows, other than those directly concerned with lakes, has discovered potentially significant impacts on ice stream dynamics, ice sheet mass balance, and supplies of water to the ocean potentially affecting circulation and nutrient productivity. Despite considerable advances in understanding there remain a number of grand challenges that must be overcome in order to improve our knowledge of these subglacial hydrological processes.

Antarctic ice dynamics - from deep past to deep future

2020 ◽  
Author(s):  
Ricarda Winkelmann ◽  
Torsten Albrecht ◽  
Julius Garbe ◽  
Jonathan Donges ◽  
Anders Levermann
Keyword(s):  
Ice Sheet ◽  
Model Parameters ◽  
Sea Level Changes ◽  
Glacial Cycles ◽  
Climatic Forcing ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
The Past ◽  
Basal Sliding ◽  
The Antarctic

<p>The Antarctic Ice Sheet has undergone extensive retreat and re-advance in its glacial-interglacial history. With progressing anthropogenic climate change, the associated ice dynamics and feedbacks could further lead to persistent and potentially irreversible ice loss from Antarctic drainage basins in the future.</p><p>Process-based models, in combination with paleo and modern records, provide the tools to reconstruct the glacial-interglacial history of the Antarctic Ice Sheet, to improve our understanding of the involved processes and critical thresholds, and to better anticipate possible future pathways.</p><p>Here we present simulations of the Antarctic Ice Sheet over the past two glacial cycles using the Parallel Ice Sheet Model PISM. As the conditions in particular at the base of the ice sheet are weakly constrained, and proxy data for the climatic forcing over the last glacial cycles is sparse, we assess the sensitivity of the model response with respect to the choice of boundary conditions. We further conduct an ensemble analysis in order to systematically constrain uncertainties with respect to representative model parameters associated with ice dynamics, climatic forcing, basal sliding and bed deformation.</p><p>Based on the insights into the dynamic threshold behavior and estimates of the ice sheet’s contributions to global sea-level changes in the past, we investigate the long-term future stability of the Antarctic Ice Sheet under different levels of global warming. We show that the ice sheet exhibits a multitude of temperature thresholds beyond which ice loss into the ocean becomes irreversible. Each of these thresholds gives rise to hysteresis behavior, meaning that the currently observed ice-sheet configuration cannot be regained even if temperatures were to be reversed to their present-day levels.</p>

The potential role of the Antarctic Ice Sheet in global biogeochemical cycles

2013 ◽  
Vol 104 (1) ◽  
pp. 55-67 ◽  
Author(s):  
J. L. Wadham ◽  
R. De'ath ◽  
F. M. Monteiro ◽  
M. Tranter ◽  
A. Ridgwell ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Focal Point ◽  
Regional Scale ◽  
Ice Sheet ◽  
Suspended Sediments ◽  
Sedimentary Basins ◽  
Antarctic Ice Sheet ◽  
Sedimentary Environments ◽  
Subglacial Lakes ◽  
The Antarctic

ABSTRACTOnce thought to be devoid of life, the Antarctic Ice Sheet is now known to be a dynamic reservoir of organic carbon and metabolically active microbial cells. At the ice-bed interface, subglacial lake and sedimentary environments support low diversity microbial populations, adapted to perennial cold, anoxia and lack of light. The dynamic exchange of water between these shallow environments conveys meltwaters and associated sediments into the coastal ocean. This, together with the release of iceberg-rafted debris to more distal coastal environments, could be important for sustaining primary productivity in the iron-limited Southern Ocean, via the release of associated nutrients and bioavailable iron. We estimate the magnitude and review the wider impacts of the potential export of nutrients (N, P, C, Si and bioavailable Fe) dissolved and associated with suspended sediments in Antarctic runoff and entombed in iceberg rafted debris. Located beneath subglacial lakes and the subglacial till complex are deep sedimentary basins up to 14 km thick, located largely around the Antarctic periphery. These sedimentary basins are largely hydrologically decoupled from shallower lake and till environments by the presence of highly consolidated sediments which limit the penetration of glacial meltwaters to depth. They provide extensive habitats for sustained microbial activity over Ma timescales, and are likely to be a focal point for the anaerobic cycling of organic carbon and other elements in the deep sub-surface. Organic carbon buried in these basins during ice sheet formation is thought to be microbially cycled to methane gas, and the methane largely stored as hydrate within sediments, stabilised by the high pressure/low temperature conditions. We conclude that the export of nutrients and biogenic gases from deep and shallow subglacial Antarctic environments designates Antarctica as a potentially important component of the Earth's carbon cycle, and highlight the importance of evaluating these potential impacts further via global and regional-scale biogeochemical modelling.

scholarly journals Impacts of Antarctic runoff changes on the Southern Ocean sea ice in an eddy-permitting sea ice-ocean model

2016 ◽  
Author(s):  
Verena Haid ◽  
Dorotea Iovino ◽  
Simona Masina
Keyword(s):  
Spatial Distribution ◽  
Sea Ice ◽  
Fresh Water ◽  
Ice Sheet ◽  
Strong Increase ◽  
Sea Ice Extent ◽  
Ice Dynamics ◽  
Current Increase ◽  
Antarctic Ice Sheet ◽  
The Antarctic

Abstract. In a warming climate, observations indicate that the sea ice extent around Antarctica has increased over the last decades. One of the suggested explanations is the stabilizing effect of increased mass loss of the Antarctic ice sheet. We investigated the sea ice response to changes in the amount and especially the spatial distribution of freshwater. We performed a sensitivity study by comparing a set of numerical simulations with additional supply of water at the Antarctic ocean surface. Here, we analyse the response of the sea ice cover and the on-shelf water column to variations in the amount and distribution of the prescribed surface freshwater flux. Our results confirm that an increase in fresh water input can increase the sea ice extent. However, a very strong increase of freshwater will eventually invert the trend. Our experiments suggest that the spatial distribution of the freshwater is of great influence. It affects sea ice dynamics and can strongly alter regional sea ice concentration and thickness. For strong regional contrasts in the freshwater addition the local change in sea ice is dominated by the dynamic response, which generally opposes the thermodynamic response. Furthermore, we find that additional coastal runoff generally leads to fresher and warmer dense shelf waters. Comparing our results with the observed trend, we estimate that the current increase of fresh water originating from the Antarctic Ice Sheet contributes between 5 % and 24 % to the trend observed in the sea ice extent.

scholarly journals Modelling the Antarctic Ice Sheet across the Mid Pleistocene Transition – Implications for Oldest Ice

2019 ◽  
Author(s):  
Johannes Sutter ◽  
Hubertus Fischer ◽  
Klaus Grosfeld ◽  
Nanna B. Karlsson ◽  
Thomas Kleiner ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Ice Core ◽  
Ice Sheet ◽  
Middle Pleistocene ◽  
Climate Modelling ◽  
Geothermal Heat ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Pleistocene Climate ◽  
The Antarctic

Abstract. The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3D continental ice sheet modelling. To this end, we present an ensemble of ice sheet simulations spanning the last 2 Myr and employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the effects of changing climate conditions, sea level and geothermal heat flux boundary conditions on the mass balance and ice dynamics of the Antarctic Ice Sheet. Our modelling results show a range of configurational ice sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate re-organisation and associated ice-dynamic changes we identify several regions conducive to conditions maintaining 1.5 Myr old ice, particularly around Dome Fuji, Dome C and Ridge B, in agreement to previous studies. This finding strengthens the notion that old ice exists in previously identified regions, while providing a dynamic continental ice sheet context.

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