Evidence for variable grounding-zone and shear-margin basal conditions across Thwaites Glacier, West Antarctica

Definitive interpretation of ice-sheet basal conditions from radar-sounding data beneath outlet-glacier grounding zones and shear margins can be problematic due to poorly constrained and spatially variable englacial attenuation rates and losses from propagation through a rough ice surface. To correct for spatially variable attenuation rates, we developed a novel radar analysis approach that provided improved empirical attenuation correction by fitting linearly variable attenuation rates along radar-sounding profiles from the ice-sheet interior to the grounding zone. We also corrected for ice-surface propagation losses by using surface echo amplitude distributions to constrain the loss of coherent power for surface reflections and two-way propagation through a rough ice surface. By applying this approach to airborne radar-sounding observations of the Thwaites Glacier catchment in West Antarctica, we produced relative reflectivity profiles, which show grounding-zone basal conditions varying across the Amundsen Sea Embayment. Additionally, these techniques provided improved characterization of basal conditions across shear margins, showing that — contrary to previous interpretations — the eastern shear margin of Thwaites Glacier corresponded to a change in basal conditions consistent with a transition from frozen to thawed bed.

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

Remote Sensing ◽

10.3390/rs11060653 ◽

2019 ◽

Vol 11 (6) ◽

pp. 653 ◽

Cited By ~ 1

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.

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Meteorological Drivers and Large-Scale Climate Forcing of West Antarctic Surface Melt

Journal of Climate ◽

10.1175/jcli-d-18-0233.1 ◽

2019 ◽

Vol 32 (3) ◽

pp. 665-684 ◽

Cited By ~ 15

Author(s):

Ryan C. Scott ◽

Julien P. Nicolas ◽

David H. Bromwich ◽

Joel R. Norris ◽

Dan Lubin

Keyword(s):

Sea Ice ◽

Ice Sheet ◽

Climate Forcing ◽

West Antarctica ◽

Sea Ice Concentration ◽

Amundsen Sea ◽

West Antarctic ◽

Ice Concentration ◽

Surface Melt ◽

Marine Air

Understanding the drivers of surface melting in West Antarctica is crucial for understanding future ice loss and global sea level rise. This study identifies atmospheric drivers of surface melt on West Antarctic ice shelves and ice sheet margins and relationships with tropical Pacific and high-latitude climate forcing using multidecadal reanalysis and satellite datasets. Physical drivers of ice melt are diagnosed by comparing satellite-observed melt patterns to anomalies of reanalysis near-surface air temperature, winds, and satellite-derived cloud cover, radiative fluxes, and sea ice concentration based on an Antarctic summer synoptic climatology spanning 1979–2017. Summer warming in West Antarctica is favored by Amundsen Sea (AS) blocking activity and a negative phase of the southern annular mode (SAM), which both correlate with El Niño conditions in the tropical Pacific Ocean. Extensive melt events on the Ross–Amundsen sector of the West Antarctic Ice Sheet (WAIS) are linked to persistent, intense AS blocking anticyclones, which force intrusions of marine air over the ice sheet. Surface melting is primarily driven by enhanced downwelling longwave radiation from clouds and a warm, moist atmosphere and by turbulent mixing of sensible heat to the surface by föhn winds. Since the late 1990s, concurrent with ocean-driven WAIS mass loss, summer surface melt occurrence has increased from the Amundsen Sea Embayment to the eastern Ross Ice Shelf. We link this change to increasing anticyclonic advection of marine air into West Antarctica, amplified by increasing air–sea fluxes associated with declining sea ice concentration in the coastal Ross–Amundsen Seas.

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High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet

Earth System Science Data Discussions ◽

10.5194/essdd-7-129-2014 ◽

2014 ◽

Vol 7 (1) ◽

pp. 129-148 ◽

Cited By ~ 4

Author(s):

K. Lindbäck ◽

R. Pettersson ◽

S. H. Doyle ◽

C. Helanow ◽

P. Jansson ◽

...

Keyword(s):

Mass Balance ◽

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Airborne Radar ◽

Ice Thickness ◽

Equilibrium Line Altitude ◽

Bed Topography ◽

Ice Surface ◽

Ice Sheet Dynamics

Abstract. We present ice thickness and bed topography maps with high spatial resolution (250 to 500 m) of a and-terminating section of the Greenland Ice Sheet derived from combined ground-based and airborne radar surveys. The data have a total area of ~12000 km2 and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Ørkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at ~1600 m above sea level. The bed topography shows highly variable subglacial trough systems, and the trough of the Isunnguata Sermia Glacier is over-deepened and reaches an elevation of several hundreds of meters below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part. The covered area is one of the most studied regions of the Greenland Ice Sheet with studies of mass balance, dynamics, and supraglacial lakes, and our combined dataset can be valuable for detailed studies of ice sheet dynamics and hydrology. The compiled datasets of ground-based and airborne radar surveys are accessible for reviewers (password protected) at doi.pangaea.de/10.1594/pangaea.830314 and will be freely available in the final revised paper.

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

10.5194/egusphere-egu2020-21391 ◽

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

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.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1512482112 ◽

2015 ◽

Vol 112 (46) ◽

pp. 14191-14196 ◽

Cited By ~ 62

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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Mid-Holocene thinning of David Glacier, Antarctica: Chronology and Controls

10.5194/tc-2020-284 ◽

2020 ◽

Author(s):

Jamey Stutz ◽

Andrew Mackintosh ◽

Kevin Norton ◽

Ross Whitmore ◽

Carlo Baroni ◽

...

Keyword(s):

Numerical Modelling ◽

Flow Line ◽

Ice Sheet ◽

Outlet Glacier ◽

Exposure Dating ◽

Ice Surface ◽

Geological Past ◽

Climate Interactions ◽

Glacier Flow ◽

Exposure Ages

Abstract. Quantitative satellite observations provide a comprehensive assessment of ice sheet mass loss over the last four decades, but limited insights into long-term drivers of ice sheet change. Geological records can extend the observational record and aid our understanding of ice sheet–climate interactions. Here we present the first millennial-scale reconstruction of David Glacier, the largest East Antarctic outlet glacier in Victoria Land. We use surface exposure dating of glacial erratics deposited on nunataks to reconstruct changes in ice surface elevation through time. We then use numerical modelling experiments to determine the drivers of glacial thinning. Thinning profiles derived from 45 10Be and 3He surface exposure ages show that David Glacier experienced rapid thinning up to 2 m/yr during the mid-Holocene (~ 6,500 years ago). Thinning stabilised at 6 kyr, suggesting initial formation of the Drygalski Ice Tongue at this time. Our work, along with terrestrial cosmogenic nuclide records from adjacent glaciers, shows simultaneous glacier thinning in this sector of the Transantarctic Mountains occurred ~ 3 kyr after the retreat of marine-based grounded ice in the western Ross Embayment. The timing and rapidity of the reconstructed thinning at David Glacier is similar to reconstructions in the Amundsen and Weddell embayments. In order to identify the potential causes of these rapid changes along the David Glacier, we use a glacier flow line model designed for calving glaciers and compare modelled results against our geological data. We show that glacier thinning and marine-based grounding line retreat is initiated by interactions between enhanced sub-ice shelf melting and reduced lateral buttressing, leading to Marine Ice Sheet Instability. Such rapid glacier thinning events are not captured in continental or sector-scale numerical modelling reconstructions for this period. Together, our chronology and modelling suggest a ~ 2,000-year period of dynamic thinning in the recent geological past.

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Automated detection and characterization of Antarctic basal units using radar sounding data: demonstration in Institute Ice Stream, West Antarctica

Annals of Glaciology ◽

10.1017/aog.2020.27 ◽

2020 ◽

Vol 61 (81) ◽

pp. 242-248 ◽

Cited By ~ 2

Author(s):

Madison L. Goldberg ◽

Dustin M. Schroeder ◽

Davide Castelletti ◽

Elisa Mantelli ◽

Neil Ross ◽

...

Keyword(s):

Conceptual Framework ◽

Ice Sheet ◽

Automatic Detection ◽

Automated Detection ◽

Observational Constraints ◽

West Antarctica ◽

Sheet Surface ◽

Unknown Composition ◽

Insight Into

AbstractBasal units – visibly distinct englacial structures near the ice-bed interface – warrant investigation for a number of reasons. Many are of unknown composition and origin, characteristics that could provide substantial insight into subglacial processes and ice-sheet history. Their significance, moreover, is not limited to near-bed depths; these units appear to dramatically influence the flow of surrounding ice. In order to enable improved characterization of these features, we develop and apply an algorithm that allows for the automatic detection of basal units. We use a tunable layer-optimized SAR processor to distinguish these structures from the bed, isochronous englacial layers and the ice-sheet surface, presenting a conceptual framework for the use of radio-echo character in the identification of ice-sheet features. We also outline a method by which our processor could be used to place observational constraints on basal units’ configuration, composition and provenance.

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Chapter 7.5 Active subglacial volcanism in West Antarctica

Geological Society London Memoirs ◽

10.1144/m55-2019-3 ◽

2021 ◽

pp. M55-2019-3

Author(s):

Enrica Quartini ◽

Donald D. Blankenship ◽

Duncan A. 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

AbstractA 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 heterogeneous, 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 under-represented. Unsurprisingly, the sites of active subglacial volcanism that 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–Siple Coast lithospheric transition.

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Variable Antarctic ice flux linked to ocean forcing, bed topography and ice shelf buttressing

10.5194/egusphere-egu21-15367 ◽

2021 ◽

Author(s):

Bertie Miles ◽

Chris Stokes ◽

Stewart Jamieson ◽

Jim Jordan ◽

Hilmar Gudmundsson ◽

...

Keyword(s):

Spatial Variability ◽

Ice Sheet ◽

East Antarctica ◽

West Antarctica ◽

Ice Shelf ◽

Observational Period ◽

Amundsen Sea ◽

Bed Topography ◽

Temporal And Spatial Variability ◽

Temporal And Spatial

It has been widely reported that ice flux from the Antarctic Ice Sheet has increased over the preceding decades. The vast majority of these increases can be attributed to the ongoing destabilization of the Amundsen Sea sector in West Antarctica, with a much more limited change in East Antarctica. However, much less attention has been focussed on the temporal and spatial variations of ice flux in Antarctica over the observational period.In this study we combine existing velocity products (ITS_LIVE and MEaSUREs) to create 12 timestamped velocity mosaics between 1999 and 2018 to investigate both overall trends in ice flux and the temporal and spatial variability across our observational period. At an ice sheet scale we report a 45 GT yr-1 increase in ice discharge in West Antarctica and no overall change in East Antarctica. However, at an individual catchment scale we observe considerable temporal and spatial variability. For West Antarctica, despite the overall increase in discharge clear periods of deceleration are observed in most individual catchments. In East Antarctica, despite overall consistency, 3-10% variations in ice discharge are observed at several major outlet glaciers (e.g. Denman, Totten, Frost, Cook, Matusevitch, Rennick). These variations can be linked to regional oceanic variability along with highly localised differences in bed topography and ice shelf calving. In some cases, this can result in neighbouring catchments simultaneously undergoing opposing trends. Improving our understanding the processes driving these short-term variations will be important in improving the accuracy of future sea level contributions from Antarctica.

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Slowdown in Antarctic mass loss from solid Earth and sea-level feedbacks

Science ◽

10.1126/science.aav7908 ◽

2019 ◽

Vol 364 (6444) ◽

pp. eaav7908 ◽

Cited By ~ 15

Author(s):

E. Larour ◽

H. Seroussi ◽

S. Adhikari ◽

E. Ivins ◽

L. Caron ◽

...

Keyword(s):

Solid Earth ◽

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

West Antarctica ◽

Spatiotemporal Resolution ◽

Amundsen Sea ◽

Polar Ice Sheets ◽

Short Time ◽

The Impact

Geodetic investigations of crustal motions in the Amundsen Sea sector of West Antarctica and models of ice-sheet evolution in the past 10,000 years have recently highlighted the stabilizing role of solid-Earth uplift on polar ice sheets. One critical aspect, however, that has not been assessed is the impact of short-wavelength uplift generated by the solid-Earth response to unloading over short time scales close to ice-sheet grounding lines (areas where the ice becomes afloat). Here, we present a new global simulation of Antarctic evolution at high spatiotemporal resolution that captures all solid Earth processes that affect ice sheets and show a projected negative feedback in grounding line migration of 38% for Thwaites Glacier 350 years in the future, or 26.8% reduction in corresponding sea-level contribution.

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