scholarly journals Basal Water Storage Variations beneath Antarctic Ice Sheet Inferred from Multi-source Satellite Data

2021 ◽  
Author(s):  
Jingyu Kang ◽  
Yang Lu ◽  
Yan Li ◽  
Zizhan Zhang ◽  
Hongling Shi
Keyword(s):  
Mass Balance ◽  
Water Storage ◽  
Ice Sheet ◽  
Satellite Observation ◽  
Inversion Method ◽  
Observation Data ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
Ice Flows ◽  
Subglacial Lakes

Abstract. Antarctic basal water storage variations (BWSV) refer to the mass variations of liquid water beneath Antarctic ice sheet. Identifying these variations is critical to understand the behaviour of ice sheet, yet it is rarely accessible to direct observation. We presented a layered gravity density forward/inversion method for estimating Antarctic BWSV from multi- source satellite observation data, and relevant models. Results reveal spatial variability of BWSV with the mean rate of 43 ± 13 Gt/yr during 2003–2009, which is 21 Gt/yr lower than basal melting rate. This indicates that the basal meltwater beneath Antarctic ice sheet is decreasing with the rate of −21 ± 13 Gt/yr, accounting for 28 % of the mass balance rate (−76 Gt/yr, Shepherd et al. (2018)), and the basal water migrations between basal drainage systems and oceans is non-ignorable in estimating basal mass balance of Antarctic ice sheet. Similar spatial distribution of basal water increases regions and locations of active subglacial lakes indicates that basal water storage in most active subglacial lakes is increasing. In most region of Antarctic ice sheet except Amundsen Sea coast region, the comparison of spatial BWSV and ice velocity displays a positive correlation between considerable basal water increases and rapid/accelerated ice flows, which indicates that BWSV appear to have an important effect on ice flows. Accordingly, we infer that further enhanced flow velocities are expected if basal water continues to increase in these regions.

scholarly journals Basal Water Storage Variations beneath Antarctic Ice Sheet

2021 ◽  
Author(s):  
Jingyu Kang ◽  
Yang Lu ◽  
Yan Li ◽  
Zizhan Zhang ◽  
Hongling Shi
Keyword(s):  
Water Discharge ◽  
Water Storage ◽  
Ice Sheet ◽  
Satellite Observation ◽  
Surface Velocity ◽  
Inversion Method ◽  
Observation Data ◽  
Ice Flows ◽  
Subglacial Lakes ◽  
Basal Melting

Abstract. Antarctic basal water storage variations (BWSV) contain basal water migrations and basal melting. Identifying these variations are critical to understand the behaviour of ice sheet, yet it is rarely accessible to direct observation. We presented a layered gravity density forward/inversion method for constructing Antarctic basal mass balance (BMB) estimates from multisource satellite observation data, and evaluated BWSV based on basal melting rate. As an example, spatial annual BWSV trend during 2003–2009 are estimated. Results reveal spatial variability of BWSV, with the rate of 46.3 Gt/y. Similar spatial distribution between basal water increases regions and locations of active subglacial lakes indicates that basal water storage in most active subglacial lakes are increasing. Comparison of spatial BWSV and ice surface velocity display a positive correlation between considerable basal water decreases and rapid ice flows, however, exceptions are when the massive rapid ice flows connected to huge ice shelves that hold up by surrounding terrains, that slows down the basal water discharge outward.

scholarly journals A Joint Inversion Estimate of Antarctic Ice Sheet Mass Balance Using Multi-Geodetic Data Sets

2019 ◽  
Vol 11 (6) ◽  
pp. 653 ◽  
Author(s):  
Chunchun Gao ◽  
Yang Lu ◽  
Zizhan Zhang ◽  
Hongling Shi
Keyword(s):  
Mass Balance ◽  
Joint Inversion ◽  
Ice Sheet ◽  
Mass Change ◽  
West Antarctica ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
Forward Models ◽  
Uplift Rates ◽  
The Antarctic

Many recent mass balance estimates using the Gravity Recovery and Climate Experiment (GRACE) and satellite altimetry (including two kinds of sensors of radar and laser) show that the ice mass of the Antarctic ice sheet (AIS) is in overall decline. However, there are still large differences among previously published estimates of the total mass change, even in the same observed periods. The considerable error sources mainly arise from the forward models (e.g., glacial isostatic adjustment [GIA] and firn compaction) that may be uncertain but indispensable to simulate some processes not directly measured or obtained by these observations. To minimize the use of these forward models, we estimate the mass change of ice sheet and present-day GIA using multi-geodetic observations, including GRACE and Ice, Cloud and land Elevation Satellite (ICESat), as well as Global Positioning System (GPS), by an improved method of joint inversion estimate (JIE), which enables us to solve simultaneously for the Antarctic GIA and ice mass trends. The GIA uplift rates generated from our JIE method show a good agreement with the elastic-corrected GPS uplift rates, and the total GIA-induced mass change estimate for the AIS is 54 ± 27 Gt/yr, which is in line with many recent GPS calibrated GIA estimates. Our GIA result displays the presence of significant uplift rates in the Amundsen Sea Embayment of West Antarctica, where strong uplift has been observed by GPS. Over the period February 2003 to October 2009, the entire AIS changed in mass by −84 ± 31 Gt/yr (West Antarctica: −69 ± 24, East Antarctica: 12 ± 16 and the Antarctic Peninsula: −27 ± 8), greater than the GRACE-only estimates obtained from three Mascon solutions (CSR: −50 ± 30, JPL: −71 ± 30, and GSFC: −51 ± 33 Gt/yr) for the same period. This may imply that single GRACE data tend to underestimate ice mass loss due to the signal leakage and attenuation errors of ice discharge are often worse than that of surface mass balance over the AIS.

Climate parameters influencing satellite-based volume and elevation changes of the Antarctic ice sheet

2020 ◽  
Author(s):  
Athul Kaitheri ◽  
Anthony Mémin ◽  
Frédérique Rémy
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
Changing Climate ◽  
Basin Scale ◽  
Elevation Changes ◽  
The Antarctic ◽  
Grace Mission

<p>Precisely quantifying the Antarctic Ice Sheet (AIS) mass balance remains a challenge as several processes compete at differing degrees in the basin-scale with regional variations. Understanding of changes in AIS has been largely based on observations from various altimetry missions and Gravity Recovery And Climate Experiment (GRACE) missions due to its scale and coverage. Analysis of linear trends in surface height variations of AIS since the early 1990s showed multiple variabilities in the rate of changes over the period of time. These observations are a reflection of various underlying ice sheet processes. Therefore understanding the processes that interact on the ice sheet is important to precisely determine the response of the ice sheet to a rapidly changing climate.</p><p>Changing climate constitutes variations in major short term processes including snow accumulation and surface melting. Variations in accumulation rate and temperature at the ice sheet surface cause changes in the firn compaction (FC) rate. Variations in the FC rate change the AIS thickness, that should be detected from altimetry, but do not change its mass, as observed by the GRACE mission. We focus our study on the seasonal and interannual changes in the elevation and mass of the AIS. We use surface elevation changes from Envisat data and gravity changes derived from the latest GRACE solutions between 10/2002 and 10/2010. As mass changes observed using the GRACE mission is strongly impacted by long term isostasy, as it involves mantle mass redistribution, we remove from all dataset an 8-year trend. We use weather variable historical data solutions including surface mass balance, temperature and wind velocities from the regional climate model RACMO2.3p2 as input to an FC model to estimate AIS elevation changes. We obtain a very good correlation between height change estimates from GRACE, Envisat and RACMO2.3p2 at several places such as along the coast of Dronning Maud Land, Wilkes land and Amundsen sea sector. Considerable differences in Oates and Mac Robertson regions, with a strong seasonal signal in Envisat estimates, reflect spatial variability in physical parameters of the surface of the AIS due to climate parameter changes such as winds.</p>

Global climate anomalies and their association with the mass balance of the Antarctic Ice Sheet

2021 ◽  
Author(s):  
Athul Kaitheri ◽  
Anthony Mémin ◽  
Frédérique Rémy
Keyword(s):  
Mass Balance ◽  
Southern Oscillation ◽  
Ice Sheet ◽  
Periodic Signal ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
Climate Anomalies ◽  
Elevation Changes ◽  
Height Change ◽  
The Antarctic

<p>Nominal mass change patterns of the Antarctic Ice Sheet (AIS) are usually altered by climate anomalies. By alternating warm and cold conditions, El Niño Southern Oscillation (ENSO) alters moisture transport, sea surface temperature, precipitation, etc in and around the AIS and potentially produces such anomalies. Indices like the Southern Oscillation Index (SOI) and the Oceanic Niño Index (ONI) robustly represent the ENSO phenomenon and is used to evaluate the characteristics of an El Niño or a La Niña. Very few studies have taken place exploring the influence of climate anomalies on the AIS and only a vague estimate of its impact is available.</p><p>Changes to the ice sheet are quantified using observations from space-borne altimetric and gravimetric missions. We use data from missions like Envisat (2002 to 2010) and Gravity Recovery And Climate Experiment (GRACE) (2002 to 2016) to estimate monthly elevation changes and mass changes respectively. Similar estimates of the changes are made using weather variables (surface mass balance (SMB) and temperature) from a regional climate model (RACMO2.3p2) combined with a firn compaction (FC) model. Inter-annual height change patterns are then extracted using empirical mode decomposition and principal component analysis to investigate a possible influence of climate anomalies on the AIS.</p><p>Elevation changes estimated from different techniques are in good agreement with each other across AIS especially in West Antarctica, Antarctic Peninsula, and along the coasts of East Antarctica. Investigating the inter-annual signals in these regions revealed a sub-4-year periodic signal in the height change patterns. This periodic behavior in the height change patterns is altered in the Antarctic Pacific (AP) sector possibly by the influence of multiple climate drivers like the Amundsen Sea Low (ASL) and the Southern Annular Mode (SAM). Height change anomaly also appears to traverse eastwards from Coats Land to Pine Island Glacier (PIG) regions passing through Dronning Maud Land (DML)  and Wilkes Land (WL) in 7 to 8 years. This is indicative of climate anomaly traversal due to the Antarctic Circumpolar Wave (ACW). Altogether, variability in the SMB of the AIS is found to be modulated by multiple climate anomalies.</p>

Repeat Subglacial Lake Drainage and Filling Beneath Thwaites Glacier, West-Antarctic Ice Sheet

2020 ◽  
Author(s):  
George Malczyk ◽  
Daniel Goldberg ◽  
Noel Gourmelen ◽  
Jan Wuite ◽  
Thomas Nagler
Keyword(s):  
Ice Sheet ◽  
Catchment Scale ◽  
Amundsen Sea ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
Subglacial Lake ◽  
West Antarctic ◽  
Lake Drainage ◽  
Subglacial Lakes

<p>Active subglacial lakes have been identified throughout Antarctica, offering a window into subglacial environments and into controls on ice dynamics. Between June 2013 and January 2014 a system of connected subglacial lakes drained in unison under the Thwaites glacier in the West Antarctic ice sheet, the first time that such a system has been observed in the Amundsen Sea Sector. Estimates based on catchment scale melt production suggested that lake drainages of this type should occur every 20 to 80 years. We collected elevations from January 2011 to December 2019 over the Thwaites lake region using the CryoSat-2 swath interferometric mode and ICEsat-2 land ice elevations, as well as ice velocity from the Sentinel-1 SAR mission since 2014. Using various elevation time series approaches, we obtain time dependent elevations over each lake. Results indicate that the upstream lakes undertake a second episode of drainage during mid-2017, only 3 years after the previous event, and that a new lake drained. Unlike the 2013-2014 episode, this new drainage episode contributed to filling one of the downstream lake with no evidence of further downstream activity. This new sub-glacial lake activity under Thwaites offer the possibility to explore lake connectivity, subglacial melt production and the interaction with ice dynamics.</p>

scholarly journals An Evaluation of Surface Climatology in State-of-the-Art Reanalyses over the Antarctic Ice Sheet

2019 ◽  
Vol 32 (20) ◽  
pp. 6899-6915 ◽  
Author(s):  
A. Gossart ◽  
S. Helsen ◽  
J. T. M. Lenaerts ◽  
S. Vanden Broucke ◽  
N. P. M. van Lipzig ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Surface Temperature ◽  
Mass Balance ◽  
Ice Sheet ◽  
Surface Mass Balance ◽  
Antarctic Ice Sheet ◽  
Near Surface ◽  
Surface Mass ◽  
Atmospheric Rivers ◽  
The Antarctic

Abstract In this study, we evaluate output of near-surface atmospheric variables over the Antarctic Ice Sheet from four reanalyses: the new European Centre for Medium-Range Weather Forecasts ERA-5 and its predecessor ERA-Interim, the Climate Forecast System Reanalysis (CFSR), and the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). The near-surface temperature, wind speed, and relative humidity are compared with datasets of in situ observations, together with an assessment of the simulated surface mass balance (approximated by precipitation minus evaporation). No reanalysis clearly stands out as the best performing for all areas, seasons, and variables, and each of the reanalyses displays different biases. CFSR strongly overestimates the relative humidity during all seasons whereas ERA-5 and MERRA-2 (and, to a lesser extent, ERA-Interim) strongly underestimate relative humidity during winter. ERA-5 captures the seasonal cycle of near-surface temperature best and shows the smallest bias relative to the observations. The other reanalyses show a general temperature underestimation during the winter months in the Antarctic interior and overestimation in the coastal areas. All reanalyses underestimate the mean near-surface winds in the interior (except MERRA-2) and along the coast during the entire year. The winds at the Antarctic Peninsula are overestimated by all reanalyses except MERRA-2. All models are able to capture snowfall patterns related to atmospheric rivers, with varying accuracy. Accumulation is best represented by ERA-5, although it underestimates observed surface mass balance and there is some variability in the accumulation over the different elevation classes, for all reanalyses.

Active subglacial volcanism in West Antarctica as assessed by airborne geophysics: Distribution and context

2020 ◽  
Author(s):  
Donald Blankenship ◽  
Enrica Quatini ◽  
Duncan Young
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Rift System ◽  
West Antarctica ◽  
The West ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Subglacial Volcanism

<p>A combination of aerogeophysics, seismic observations and direct observation from ice cores and subglacial sampling has revealed at least 21 sites under the West Antarctic Ice sheet consistent with active volcanism (where active is defined as volcanism that has interacted with the current manifestation of the West Antarctic Ice Sheet). Coverage of these datasets is heterogenous, potentially biasing the apparent distribution of these features. Also, the products of volcanic activity under thinner ice characterized by relatively fast flow are more prone to erosion and removal by the ice sheet, and therefore potentially underrepresented. Unsurprisingly, the sites of active subglacial volcanism we have identified often overlap with areas of relatively thick ice and slow ice surface flow, both of which are critical conditions for the preservation of volcanic records. Overall, we find the majority of active subglacial volcanic sites in West Antarctica concentrate strongly along the crustal thickness gradients bounding the central West Antarctic Rift System, complemented by intra-rift sites associated with the Amundsen Sea to Siple Coast lithospheric transition.</p>

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 Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin

2015 ◽  
Vol 112 (46) ◽  
pp. 14191-14196 ◽  
Author(s):  
Johannes Feldmann ◽  
Anders Levermann
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Horizontal Resolution ◽  
West Antarctica ◽  
Amundsen Sea ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Topographic Features ◽  
Global Sea Level

The future evolution of the Antarctic Ice Sheet represents the largest uncertainty in sea-level projections of this and upcoming centuries. Recently, satellite observations and high-resolution simulations have suggested the initiation of an ice-sheet instability in the Amundsen Sea sector of West Antarctica, caused by the last decades’ enhanced basal ice-shelf melting. Whether this localized destabilization will yield a full discharge of marine ice from West Antarctica, associated with a global sea-level rise of more than 3 m, or whether the ice loss is limited by ice dynamics and topographic features, is unclear. Here we show that in the Parallel Ice Sheet Model, a local destabilization causes a complete disintegration of the marine ice in West Antarctica. In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine ice-sheet instability fully unfolds and is not halted by topographic features. In fact, the ice loss in Amundsen Sea sector shifts the catchment's ice divide toward the Filchner–Ronne and Ross ice shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, Antarctica will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia.

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