Technologies for retrieving sediment cores in Antarctic subglacial settings

Accumulations of sediment beneath the Antarctic Ice Sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings. Retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies. This paper briefly reviews the history of sediment sampling in subglacial environments. It then outlines some of the technological challenges and constraints in developing the corers being used in sub-ice shelf settings (e.g. George VI Ice Shelf and Larsen Ice Shelf), under ice streams (e.g. Rutford Ice Stream), at or close to the grounding line (e.g. Whillans Ice Stream) and in subglacial lakes deep under the ice sheet (e.g. Lake Ellsworth). The key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures.

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Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

Annals of Glaciology ◽

10.3189/s0260305500006364 ◽

1988 ◽

Vol 11 ◽

pp. 77-82 ◽

Cited By ~ 3

Author(s):

D. R. MacAyeal ◽

R. A. Bindschadler ◽

K. C. Jezek ◽

S. Shabtaie

Keyword(s):

Numerical Model ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Stream Discharge ◽

Ice Stream ◽

History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

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Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

The Cryosphere ◽

10.5194/tc-7-1721-2013 ◽

2013 ◽

Vol 7 (6) ◽

pp. 1721-1740 ◽

Cited By ~ 62

Author(s):

S. J. Livingstone ◽

C. D. Clark ◽

J. Woodward ◽

J. Kingslake

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Simplified Approach ◽

Subglacial Lake ◽

Ice Stream ◽

Geophysical Surveys ◽

Subglacial Lakes ◽

The Antarctic ◽

Subglacial Drainage

Abstract. We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

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Quantifying the Jakobshavn Effect: Jakobshavn Isbrae, Greenland, compared to Byrd Glacier, Antarctica

The Cryosphere Discussions ◽

10.5194/tcd-8-2043-2014 ◽

2014 ◽

Vol 8 (2) ◽

pp. 2043-2118

Author(s):

T. Hughes ◽

A. Sargent ◽

J. Fastook ◽

K. Purdon ◽

J. Li ◽

...

Keyword(s):

Ice Sheets ◽

Greenland Ice Sheet ◽

Force Balance ◽

Ice Age ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Ice Stream ◽

Visual Understanding ◽

Subglacial Lakes

Abstract. The Jakobshavn Effect is a series of positive feedback mechanisms that was first observed on Jakobshavn Isbrae, which drains the west-central part of the Greenland Ice Sheet and enters Jakobshavn Isfjord at 69°10'. These mechanisms fall into two categories, reductions of ice-bed coupling beneath an ice stream due to surface meltwater reaching the bed, and reductions in ice-shelf buttressing beyond an ice stream due to disintegration of a laterally confined and locally pinned ice shelf. These uncoupling and unbuttressing mechanisms have recently taken place for Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland, respectively. For Byrd Glacier, no surface meltwater reaches the bed. That water is supplied by drainage of two large subglacial lakes where East Antarctic ice converges strongly on Byrd Glacier. Results from modeling both mechanisms are presented here. We find that the Jakobshavn Effect is not active for Byrd Glacier, but is active for Jakobshavn Isbrae, at least for now. Our treatment is holistic in the sense it provides continuity from sheet flow to stream flow to shelf flow. It relies primarily on a force balance, so our results cannot be used to predict long-term behavior of these ice streams. The treatment uses geometrical representations of gravitational and resisting forces that provide a visual understanding of these forces, without involving partial differential equations and continuum mechanics. The Jakobshavn Effect was proposed to facilitate terminations of glaciation cycles during the Quaternary Ice Age by collapsing marine parts of ice sheets. This is unlikely for the Antarctic and Greenland ice sheets, based on our results for Byrd Glacier and Jakobshavn Isbrae, without drastic climate warming in high polar latitudes. Warming would affect other Antarctic ice streams already weakly buttressed or unbuttressed by an ice shelf. Ross Ice Shelf would still protect Byrd Glacier.

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Thermal regime and dynamics of the West Antarctic ice sheet

Annals of Glaciology ◽

10.3189/172756404781814203 ◽

2004 ◽

Vol 39 ◽

pp. 85-92 ◽

Cited By ~ 40

Author(s):

Hermann Engelhardt

Keyword(s):

Basal Layer ◽

Ice Sheet ◽

Ice Streams ◽

The West ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Whillans Ice Stream ◽

Kamb Ice Stream

AbstractThe temperature–depth profiles measured in 22 boreholes drilled on the West Antarctic ice sheet exhibit two distinctly different thermal states of its basal ice. The warm state shows on Siple Dome and on Whillans Ice Stream. A relatively colder state, found at the Unicorn, Kamb Ice Stream (former Ice Stream C) and Bindschadler Ice Stream (former Ice Stream D), has basal temperature gradients greater than 50 K km–1. A large block of cold ice stranded and frozen to the bed at the Unicorn and simultaneously much warmer ice existing only a few kilometers across the Dragon shear margin in fast-moving Alley Ice Stream (former Ice Stream B2) poses a paradox. The relatively cold ice at the Unicorn must have come from a source different from the present Whillans Ice Stream catchment area. It is hypothesized that the Unicorn paradox was created by a super-surge. Also, the stagnant Siple Ice Stream, many relict shear margins, cold patches of ice at the Crary Ice Rise, ice rafts embedded in the Ross Ice Shelf, all point to a major event triggered either by an internal instability or by a subareal volcanic eruption. Most of these features appeared to have been formed about 500 years ago. Subsequent freeze-on of a 10–20m thick basal layer of debris-laden ice and water loss caused a slowdown of ice streams and, in the case of Kamb Ice Stream, an almost complete stoppage.

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Past ice sheet-seabed interactions in the northeastern Weddell Sea Embayment, Antarctica

10.5194/tc-2019-271 ◽

2019 ◽

Author(s):

Jan Erik Arndt ◽

Robert D. Larter ◽

Claus-Dieter Hillenbrand ◽

Simon H. Sørli ◽

Matthias Forwick ◽

...

Keyword(s):

Ice Sheet ◽

Weddell Sea ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Seafloor Morphology ◽

Ice Stream ◽

Time Period ◽

Single Location ◽

The Antarctic ◽

Near Future

Abstract. The Antarctic Ice Sheet extent in the Weddell Sea Embayment (WSE) during the Last Glacial Maximum (LGM; ca. 19–25 calibrated kiloyears before present, cal. ka BP) and its subsequent retreat from the shelf are poorly constrained, with two conflicting scenarios being discussed. Today, the modern Brunt Ice Shelf, the last remaining ice shelf in the northeastern WSE, is only pinned at a single location and recent crevasse development may lead to its rapid disintegration in the near future. We investigated the seafloor morphology on the northeastern WSE shelf and discuss its implications, in combination with marine geological records, for reconstructions of the past behaviour of this sector of the East Antarctic Ice Sheet (EAIS), including ice-seafloor interactions. Our data show that an ice stream flowed through Stancomb-Wills Trough and acted as the main conduit for EAIS drainage during the LGM. Post-LGM ice-stream retreat occurred stepwise, with at least three documented grounding line still stands, and the trough had become free of grounded ice by ~10.5 cal. ka BP. In contrast, slow-flowing ice once covered the shelf in Brunt Basin and extended westwards toward McDonald Bank. During a later time period, only floating ice was present within Brunt Basin, but large ‘ice slabs’ enclosed within the ice shelf occasionally ran aground at the eastern side of McDonald Bank, forming ten unusual ramp-shaped seabed features. These ramps are the result of temporary ice-shelf grounding events buttressing the ice further upstream. To the west of this area, Halley Trough very likely was free of grounded ice during the LGM, representing a potential refuge for benthic shelf fauna at this time.

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Past ice sheet–seabed interactions in the northeastern Weddell Sea embayment, Antarctica

The Cryosphere ◽

10.5194/tc-14-2115-2020 ◽

2020 ◽

Vol 14 (6) ◽

pp. 2115-2135

Author(s):

Jan Erik Arndt ◽

Robert D. Larter ◽

Claus-Dieter Hillenbrand ◽

Simon H. Sørli ◽

Matthias Forwick ◽

...

Keyword(s):

Ice Sheet ◽

Weddell Sea ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Seafloor Morphology ◽

Ice Stream ◽

Time Period ◽

Single Location ◽

The Antarctic ◽

Near Future

Abstract. The Antarctic ice sheet extent in the Weddell Sea embayment (WSE) during the Last Glacial Maximum (LGM; ca. 19–25 calibrated kiloyears before present, ka cal BP) and its subsequent retreat from the shelf are poorly constrained, with two conflicting scenarios being discussed. Today, the modern Brunt Ice Shelf, the last remaining ice shelf in the northeastern WSE, is only pinned at a single location and recent crevasse development may lead to its rapid disintegration in the near future. We investigated the seafloor morphology on the northeastern WSE shelf and discuss its implications, in combination with marine geological records, to create reconstructions of the past behaviour of this sector of the East Antarctic Ice Sheet (EAIS), including ice–seafloor interactions. Our data show that an ice stream flowed through Stancomb-Wills Trough and acted as the main conduit for EAIS drainage during the LGM in this sector. Post-LGM ice stream retreat occurred stepwise, with at least three documented grounding-line still-stands, and the trough had become free of grounded ice by ∼10.5 ka cal BP. In contrast, slow-flowing ice once covered the shelf in Brunt Basin and extended westwards toward McDonald Bank. During a later time period, only floating ice was present within Brunt Basin, but large “ice slabs” enclosed within the ice shelf occasionally ran aground at the eastern side of McDonald Bank, forming 10 unusual ramp-shaped seabed features. These ramps are the result of temporary ice shelf grounding events buttressing the ice further upstream. To the west of this area, Halley Trough very likely was free of grounded ice during the LGM, representing a potential refuge for benthic shelf fauna at this time.

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Effect of Improved Bedrock Geometry on Antarctic Vulnerability to Regional Ice Shelf Collapse

10.5194/egusphere-egu2020-10033 ◽

2020 ◽

Author(s):

Daniel Martin ◽

Stephen Cornford ◽

Esmond Ng

Keyword(s):

Recent Work ◽

Sea Level ◽

Ice Sheet ◽

Mass Conservation ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Starting Point ◽

The Antarctic

<p>The Antarctic Ice Sheet (AIS) is vulnerable to the thinning or even the collapse of its floating ice shelves, which tend to buttress ice streams. Any reduction in buttressing results in acceleration and thinning upstream and potentially the onset of Marine Ice Sheet Instability. Recent work demonstrates that West Antarctica is vulnerable to sustained disintegration in any of its major marine outlets, resulting in 2-3 m sea level rise over 1000 years. At the same time regions in East Antarctica are vulnerable only to the loss of local ice shelves. However, most of this work has used the Bedmap2 dataset as a starting point. Since the release of Bedmap2 in 2012, there has been a sustained campaign of observations, along with improved interpolation techniques based on mass conservation. The resulting datasets, including the recently released BedMachine dataset, incorporate much-improved bedrock and thickness data compared to what was available in Bedmap2.&#160;</p><p>We reproduce our previous examination of the millennial-scale vulnerability of the AIS to the loss of its shelves to examine the effect of this improvement on projected Antarctic vulnerability, paying special attention to regions like the Aurora Basin which were under-constrained in Bedmap2.</p>

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Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

The Cryosphere ◽

10.5194/tc-10-2971-2016 ◽

2016 ◽

Vol 10 (6) ◽

pp. 2971-2980 ◽

Cited By ~ 3

Author(s):

Byeong-Hoon Kim ◽

Choon-Ki Lee ◽

Ki-Weon Seo ◽

Won Sang Lee ◽

Ted Scambos

Keyword(s):

Water System ◽

Topographic Feature ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Subglacial Lake ◽

Ice Stream ◽

Grounding Line ◽

Subglacial Lakes ◽

Kamb Ice Stream

Abstract. We identify two previously unknown subglacial lakes beneath the stagnated trunk of the Kamb Ice Stream (KIS). Rapid fill-drain hydrologic events over several months are inferred from surface height changes measured by CryoSat-2 altimetry and indicate that the lakes are probably connected by a subglacial drainage network, whose structure is inferred from the regional hydraulic potential and probably links the lakes. The sequential fill-drain behavior of the subglacial lakes and concurrent rapid thinning in a channel-like topographic feature near the grounding line implies that the subglacial water repeatedly flows from the region above the trunk to the KIS grounding line and out beneath the Ross Ice Shelf. Ice shelf elevation near the hypothesized outlet is observed to decrease slowly during the study period. Our finding supports a previously published conceptual model of the KIS shutdown stemming from a transition from distributed flow to well-drained channelized flow of subglacial water. However, a water-piracy hypothesis in which the KIS subglacial water system is being starved by drainage in adjacent ice streams is also supported by the fact that the degree of KIS trunk subglacial lake activity is relatively weaker than those of the upstream lakes.

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Rock debris in an Antarctic ice shelf

Annals of Glaciology ◽

10.3189/2012aog60a014 ◽

2012 ◽

Vol 53 (60) ◽

pp. 235-240 ◽

Cited By ~ 11

Author(s):

K.W. Nicholls ◽

H.F.J. Corr ◽

K. Makinson ◽

C.J. Pudsey

Keyword(s):

Sea Water ◽

Ice Sheet ◽

Radar Data ◽

Coarse Sand ◽

Potential Mechanism ◽

Ice Shelf ◽

Ice Streams ◽

History Of ◽

Seaward Edge

AbstractWe have discovered a band of stones and coarse sand in the Ronne Ice Shelf, Antarctica, some 60 m above the ice shelf’s base, 40 km from its seaward edge and 420 km from the point where the ice originally went afloat. A study of ice-sounding radar data from across the Ronne Ice Shelf has revealed other areas likely to contain debris in significant quantities. It appears that basal debris at the margins of ice streams feeding the ice shelf can be buried in the ice shelf by sea water freezing-on at the ice-shelf base. These findings are evidence for a mechanism active in a present-day ice-sheet/shelf system, which enables icebergs to transport large volumes of ice-rafted debris, and which also provides a potential mechanism for the formation of ice rises near ice fronts. We anticipate that a seismics study of debris melted from the ice shelf and deposited beneath will provide a valuable control on the history of ice-shelf–ocean interactions.

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