scholarly journals Antarctic subglacial lakes drain through sediment-floored canals: theory and model testing on real and idealized domains

2017 ◽  
Vol 11 (1) ◽  
pp. 381-405 ◽  
Author(s):  
Sasha P. Carter ◽  
Helen A. Fricker ◽  
Matthew R. Siegfried
Keyword(s):  
Distributed System ◽  
Process Model ◽  
Ice Sheet ◽  
Drainage System ◽  
Drainage Water ◽  
Process Models ◽  
Altimeter Data ◽  
Laser Altimeter ◽  
Ice Stream ◽  
Subglacial Lakes

Abstract. Over the past decade, satellite observations of ice surface height have revealed that active subglacial lake systems are widespread under the Antarctic Ice Sheet, including the ice streams. For some of these systems, additional observations of ice-stream motion have shown that lake activity can affect ice-stream dynamics. Despite all this new information, we still have insufficient understanding of the lake-drainage process to incorporate it into ice-sheet models. Process models for drainage of ice-dammed lakes based on conventional R-channels incised into the base of the ice through melting are unable to reproduce the timing and magnitude of drainage from Antarctic subglacial lakes estimated from satellite altimetry given the low hydraulic gradients along which such lakes drain. We have developed an alternative process model, in which channels are mechanically eroded into the underlying deformable subglacial sediment. When applied to the known active lakes of the Whillans–Mercer ice-stream system, the model successfully reproduced both the inferred magnitudes and recurrence intervals of lake-volume changes, derived from Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data for the period 2003–2009. Water pressures in our model changed as the flood evolved: during drainage, water pressures initially increased as water flowed out of the lake primarily via a distributed system, then decreased as the channelized system grew, establishing a pressure gradient that drew water away from the distributed system. This evolution of the drainage system can result in the observed internal variability of ice flow over time. If we are correct that active subglacial lakes drain through canals in the sediment, this mechanism also implies that active lakes are typically located in regions underlain by thick subglacial sediment, which may explain why they are not readily observed using radio-echo-sounding techniques.

scholarly journals Antarctic subglacial lakes drain through sediment-floored canals: Theory and model testing on real and idealized domains

2016 ◽  
Author(s):  
Sasha P. Carter ◽  
Helen A. Fricker ◽  
Matthew R. Siegfried
Keyword(s):  
Distributed System ◽  
Process Model ◽  
Ice Sheet ◽  
Drainage System ◽  
Drainage Water ◽  
Process Models ◽  
Altimeter Data ◽  
Laser Altimeter ◽  
Ice Stream ◽  
Subglacial Lakes

Abstract. Over the past decade, satellite observations of ice surface height have revealed that active subglacial lake systems are widespread under the Antarctic ice sheet, including the ice streams. For some of these systems, additional observations of ice stream motion have shown that lake activity can affect ice-stream dynamics. Despite all this new information, we still have insufficient understanding of the lake-drainage process to incorporate it into ice sheet models. Process models for drainage of ice-dammed lakes based on conventional "R-channels" incised into the base of the ice through melting are unable to reproduce the timing and magnitude of drainage from Antarctic subglacial lakes estimated from satellite altimetry given the low hydraulic gradients along which such lakes drain. We have developed an alternative process model, in which channels are mechanically eroded into the underlying deformable subglacial sediment. When applied to the known active lakes of the Whillans/Mercer ice stream system, the model successfully reproduced both the inferred magnitudes and recurrence intervals of lake volume changes, derived from Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data for the period 2003–2009. Water pressures in our model changed as the flood evolved: during drainage, water pressures initially increased as water flowed out of the lake primarily via a distributed system, then decreased as the channelized system grew, establishing a pressure gradient that drew water away from the distributed system. This evolution of the drainage system can result in the observed internal variability of ice flow over time. If we are correct that active subglacial lakes drain through canals in the sediment, this mechanism also implies that active lakes are typically located in regions underlain by thick subglacial sediment, which may explain why they are not readily observed using radio-echo sounding techniques.

scholarly journals An inventory of active subglacial lakes in Antarctica detected by ICESat (2003–2008)

2009 ◽  
Vol 55 (192) ◽  
pp. 573-595 ◽  
Author(s):  
Benjamin E. Smith ◽  
Helen A. Fricker ◽  
Ian R. Joughin ◽  
Slawek Tulaczyk
Keyword(s):  
Surface Deformation ◽  
Water Movement ◽  
Ice Sheet ◽  
Altimeter Data ◽  
Laser Altimeter ◽  
Ice Cloud ◽  
Hydrologic Systems ◽  
Glacier Flow ◽  
Subglacial Lakes ◽  
Response To Water

AbstractThrough the detection of surface deformation in response to water movement, recent satellite studies have demonstrated the existence of subglacial lakes in Antarctica that fill and drain on timescales of months to years. These studies, however, were confined to specific regions of the ice sheet. Here we present the first comprehensive study of these ‘active’ lakes for the Antarctic ice sheet north of 86° S, based on 4.5 years (2003–08) of NASA’s Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Our analysis has detected 124 lakes that were active during this period, and we estimate volume changes for each lake. The ICESat-detected lakes are prevalent in coastal Antarctica, and are present under most of the largest ice-stream catchments. Lakes sometimes appear to transfer water from one to another, but also often exchange water with distributed sources undetectable by ICESat, suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow. Thus, these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds, but also may withdraw water at other times to slow flow.

scholarly journals Analysis of ice plains of the Filchner–Ronne Ice Shelf, Antarctica, using ICESat laser altimetry

2011 ◽  
Vol 57 (205) ◽  
pp. 965-975 ◽  
Author(s):  
Kelly M. Brunt ◽  
Helen A. Fricker ◽  
Laurie Padman
Keyword(s):  
Ice Sheet ◽  
Altimeter Data ◽  
Ice Shelf ◽  
Laser Altimeter ◽  
Ice Cloud ◽  
Ice Stream ◽  
Rapid Changes ◽  
Grounding Line ◽  
Ice Sheet Mass Balance ◽  
Bed Slope

AbstractWe use repeat-track laser altimeter data from the Ice, Cloud and land Elevation Satellite (ICESat) to map the grounding zone (GZ) of the Filchner–Ronne Ice Shelf, Antarctica. Ice flexure in the GZ occurs as the ice shelf responds to ocean-height changes due primarily to tides. We have identified three ‘ice plains’, regions of low surface slope near the GZ where the ice is close to hydrostatic equilibrium: one on Institute Ice Stream; another to its east; and another west of Foundation Ice Stream. The vertical information from repeated ICESat tracks enables us to study the topography, state of flotation and flexure characteristics across these features. In regions of ephemeral grounding, tidal migration of the grounding line allows us to estimate bed slope (∼1–2 × 10−3). From these studies we develop a classification scheme for ice plains, expressed in terms of the evolution, or ‘life cycle’, of these features. A lightly grounded ice plain progresses to a state of ephemeral grounding as the ice sheet thins near the GZ. Once sufficient thinning has occurred, the ice plain becomes a fully floating, relict ice plain with an undulated surface topography similar to that of lightly grounded ice; we expect viscous relaxation to a smooth ice-shelf surface to occur over a timescale of decades. Our improved insight into ice-plain evolution suggests added complexity in modeling ice in the vicinity of the GZ, and a role for ice-plain observations as a guide to relatively rapid changes in ice-sheet mass balance.

scholarly journals Active lakes in Antarctica survive on a sedimentary substrate – Part 1: Theory

2015 ◽  
Vol 9 (2) ◽  
pp. 2053-2099 ◽  
Author(s):  
S. P. Carter ◽  
H. A. Fricker ◽  
M. R. Siegfried
Keyword(s):  
Process Model ◽  
Ice Sheet ◽  
Process Models ◽  
Ice Streams ◽  
Subglacial Lake ◽  
Lake Volume ◽  
Hydraulic Gradients ◽  
Lake Drainage ◽  
Subglacial Lakes ◽  
Lake Systems

Abstract. Over the past decade satellite observations have revealed that active subglacial lake systems are widespread under the Antarctic ice sheet, including the ice streams, yet we have insufficient understanding of the lake-drainage process to incorporate it into ice sheet models. Process models for drainage of ice-dammed lakes based on conventional "R-channels" incised into the base of the ice through melting are unable to reproduce the timing and magnitude of drainage from Antarctic subglacial lakes estimated from satellite altimetry given the low hydraulic gradients along which such lakes drain. We developed a process model in which channels are mechanically eroded into deformable subglacial sediment (till) instead ("T-channel"). When applied to the known lakes of the Whillans/Mercer system, the model successfully reproduced the key characteristics of estimated lake volume changes for the period 2003–2009. If our model is realistic, it implies that most active lakes are shallow and only exist in the presence of saturated sediment, explaining why they are difficult to detect with classical radar methods. It also implies that the lake-drainage process is sensitive to the composition and strength of the underlying till, suggesting that models could be improved with a realistic treatment of sediment – interfacial water exchange.

scholarly journals Measurement of ice-sheet topography using satellite-radar interferometry

1996 ◽  
Vol 42 (140) ◽  
pp. 10-22 ◽  
Author(s):  
Ian Joughin ◽  
Dale Winebrenner ◽  
Mark Fahnestock ◽  
Ron Kwok ◽  
William Krabill
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Displacement ◽  
Horizontal Resolution ◽  
Radar Interferometry ◽  
Altimeter Data ◽  
Laser Altimeter ◽  
Digital Elevation ◽  
Satellite Radar ◽  
Ice Sheet Topography

AbstractDetailed digital elevation models (DEMs) do not exist for much of the Greenland and Antartic ice sheets. Radar altimetry is at present the primary, in many cases the only, source of topographic data over the ice sheets, but the horizontal resolution of such data is coarse. Satellite-radar interferometry uses the phase difference between pairs of synthetic aperture radar (SAR) images to measure both ice-sheet topography and surface displacement. We have applied this technique using ERS-1 SAR data to make detailed (i.e. 80 m horizontal resolution) maps of surface topography in a 100 km by 300 km strip in West Greenland, extending northward from just above Jakobshavns Isbræ. Comparison with а 76 km long line of airborne laser-altimeter data shows that We have achieved a relative accuracy of 2.5 m along the profile. These observations provide a detailed view of dynamically Supported topography near the margin of an ice sheet. In the final section We compare our estimate of topography with phase contours due to motion, and confirm our earlier analysis concerning vertical ice-sheet motion and complexity in ERS-1 SAR interferograms.

scholarly journals A comparison of Greenland ice-sheet volume changes derived from altimetry measurements

2008 ◽  
Vol 54 (185) ◽  
pp. 203-212 ◽  
Author(s):  
Robert Thomas ◽  
Curt Davis ◽  
Earl Frederick ◽  
William Krabill ◽  
Yonghong Li ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Time Interval ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Laser Altimeter ◽  
The North ◽  
Radar Waveforms ◽  
Summer Temperatures

AbstractWe compare rates of surface-elevation change on the Greenland ice sheet derived from European Remote-sensing Satellite-2 (ERS-2) radar-altimeter data with those obtained from laser-altimeter data collected over nearly the same time periods. Radar-altimeter data show more rapid thickening (9 ± 1 cm a−1 above 1500 m elevation in the north, and 3 ± 1 cm a−1 above 2000 m in the south) than the laser estimates, possibly caused by a lifting of the radar-reflection horizon associated with changes in the snowpack, such as those caused by progressively increased surface melting, as summer temperatures rise. Over all the ice sheet above 2000 m, this results in an ERS-derived volume balance ∼75 ± 15 km3 a−1 more positive than that from laser data. This bias between laser and radar estimates of elevation change varies spatially and temporally, so cannot at present be corrected without independent surveys such as those presented here. At lower elevations, comparison of detailed repeat laser surveys over Jakobshavn Isbræ with ERS results over the same time interval shows substantial ERS underestimation of ice-thinning rates. This results partly from missing data because of ‘bad’ radar waveforms over the very rough surface topography, and partly from the tendency for large radar footprints to sample preferentially local high points in the topography, thus missing regions of most rapid thinning along glacier depressions.

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

2013 ◽  
Vol 7 (6) ◽  
pp. 1721-1740 ◽  
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.

scholarly journals Investigating the stability of subglacial lakes with a full Stokes ice-sheet model

2008 ◽  
Vol 54 (185) ◽  
pp. 353-361 ◽  
Author(s):  
Frank Pattyn
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Potential Gradient ◽  
Surface Slope ◽  
Ice Flow ◽  
Subglacial Lake ◽  
Lake Drainage ◽  
Subglacial Lakes ◽  
The Impact ◽  
Subglacial Drainage

AbstractDespite the large amount of subglacial lakes present underneath the East Antarctic ice sheet and the melt processes involved, the hydrology beneath the ice sheet is poorly understood. Changes in subglacial potential gradients may lead to subglacial lake outbursts, discharging excess water through a subglacial drainage system underneath the ice sheet. Such processes can eventually lead to an increase in ice flow. In this paper, a full Stokes numerical ice-sheet model was employed which takes into account the ice flow over subglacial water bodies in hydrostatic equilibrium with the overlying ice. Sensitivity experiments were carried out for small perturbations in ice flow and basal melt rate as a function of ice thickness, general surface slope, ice viscosity and lake size, in order to investigate their influence on the subglacial potential gradient and the impact on subglacial lake drainage. Experiments clearly demonstrate that small changes in surface slope are sufficient to start and sustain episodic subglacial drainage events. Lake drainage can therefore be regarded as a common feature of the subglacial hydrological system and may influence, to a large extent, the present and future behavior of large ice sheets.

scholarly journals Active subglaical lakes beneath the stagnant trunk of Kamb Ice Stream: evidence of channelized subglacial flow

2016 ◽  
Author(s):  
Byeong-Hoon Kim ◽  
Choon-Ki Lee ◽  
Ki-Weon Seo ◽  
Won Sang Lee ◽  
Ted Scambos
Keyword(s):  
Ice Sheet ◽  
Drainage Network ◽  
Sheet Flow ◽  
Subglacial Lake ◽  
Ice Stream ◽  
Grounding Line ◽  
Subglacial Lakes ◽  
Kamb Ice Stream

Abstract. We have identified two new subglacial lakes beneath the stagnated trunk of Kamb Ice Stream (KIS). Rapid fill-drain hydrologic events are inferred from Cryosat-2 altimetry, indicating that the lakes are connected by a drainage network. The orientation of the drainage network is inferred from the regional hydraulic potential, and clearly links the lake areas. The behavior of the subglacial lakes and strong thinning observed at the outlet near the grounding line implies that the subglacial water persistently flows from the region above the trunk to grounding line of KIS. In addition, the ice sheet in the KIS trunk estuary is thinning rapidly, and the thinning is accelerated by the activity of subglacial lake. We suggest that a transition from sheet flow of sub-glacial water to well-drained channelized flow may explain the shutdown of Kamb Ice Stream.

scholarly journals Technologies for retrieving sediment cores in Antarctic subglacial settings

2016 ◽  
Vol 374 (2059) ◽  
pp. 20150056 ◽  
Author(s):  
Dominic A. Hodgson ◽  
Michael J. Bentley ◽  
James A. Smith ◽  
Julian Klepacki ◽  
Keith Makinson ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
History Of ◽  
Subglacial Lakes ◽  
Physical And Chemical ◽  
The Antarctic

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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