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Robel AA, Sim SJ, Meyer C, Siegfried MR, Gustafson CD. Contemporary ice sheet thinning drives subglacial groundwater exfiltration with potential feedbacks on glacier flow. SCIENCE ADVANCES 2023; 9:eadh3693. [PMID: 37595049 PMCID: PMC10438444 DOI: 10.1126/sciadv.adh3693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 07/19/2023] [Indexed: 08/20/2023]
Abstract
Observations indicate that groundwater-laden sedimentary aquifers are extensive beneath large portions of the Greenland and Antarctic ice sheets. A reduction in the mechanical loading of aquifers is known to lead to groundwater exfiltration, a discharge of groundwater from the aquifer. Here, we provide a simple expression predicting exfiltration rates under a thinning ice sheet. Using contemporary satellite altimetry observations, we predict that exfiltration rates may reach tens to hundreds of millimeters per year under the fastest thinning parts of the Antarctic Ice Sheet. In parts of West Antarctica, predicted rates of exfiltration would cause the total subglacial water discharge rate to be nearly double what is currently predicted from subglacial basal melting alone. Continued Antarctic Ice Sheet thinning into the future guarantees that the rate and potential importance of exfiltration will only continue to grow. Such an increase in warm, nutrient-laden subglacial water discharge would cause changes in ice sliding, melt of basal ice and marine biological communities.
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Affiliation(s)
- Alexander A. Robel
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30318, USA
| | - Shi J. Sim
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30318, USA
| | - Colin Meyer
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA
| | - Matthew R. Siegfried
- Hydrologic Science and Engineering Program, Department of Geophysics, Colorado School of Mines, Golden, CO 80401, USA
| | - Chloe D. Gustafson
- U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center, Lakewood, CO 80225, USA
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Gustafson CD, Key K, Siegfried MR, Winberry JP, Fricker HA, Venturelli RA, Michaud AB. A dynamic saline groundwater system mapped beneath an Antarctic ice stream. Science 2022; 376:640-644. [PMID: 35511981 DOI: 10.1126/science.abm3301] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Antarctica's fast-flowing ice streams drain the ice sheet, with their velocity modulated by subglacial water systems. Current knowledge of these water systems is limited to the shallow portions near the ice-bed interface, but hypothesized deeper groundwater could also influence ice streaming. Here, we use magnetotelluric and passive seismic data from Whillans Ice Stream, West Antarctica, to provide the first observations of deep sub-ice stream groundwater. Our data reveal a volume of groundwater within a >1-kilometer-thick sedimentary basin that is more than an order of magnitude larger than the known subglacial system. A vertical salinity gradient indicates exchange between paleo seawater at depth and contemporary basal meltwater above. Our results provide new constraints for subglacial water systems that affect ice streaming and subglacial biogeochemical processes.
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Affiliation(s)
- Chloe D Gustafson
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA.,Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
| | - Kerry Key
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA
| | - Matthew R Siegfried
- Hydrologic Science and Engineering Program, Department of Geophysics, Colorado School of Mines, Golden, CO, USA
| | - J Paul Winberry
- Department of Geological Sciences, Central Washington University, Ellensburg, WA, USA
| | - Helen A Fricker
- Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
| | - Ryan A Venturelli
- Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO, USA
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3
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Zoet LK, Iverson NR. A slip law for glaciers on deformable beds. Science 2020; 368:76-78. [PMID: 32241945 DOI: 10.1126/science.aaz1183] [Citation(s) in RCA: 50] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 02/12/2020] [Indexed: 11/02/2022]
Abstract
Slip of marine-terminating ice streams over beds of deformable till is responsible for most of the contribution of the West Antarctic Ice Sheet to sea level rise. Flow models of the ice sheet and till-bedded glaciers elsewhere require a law that relates slip resistance, slip velocity, and water pressure at the bed. We present results of experiments in which pressurized ice at its melting temperature is slid over a water-saturated till bed. Steady-state slip resistance increases with slip velocity owing to sliding of ice across the bed, but above a threshold velocity, till shears at its rate-independent Coulomb strength. These results motivate a generalized slip law for glacier-flow models that combines processes of hard-bedded sliding and bed deformation.
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Affiliation(s)
- Lucas K Zoet
- Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA. .,Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011, USA
| | - Neal R Iverson
- Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011, USA
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Christoffersen P, Bougamont M, Hubbard A, Doyle SH, Grigsby S, Pettersson R. Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture. Nat Commun 2018. [PMID: 29540693 PMCID: PMC5852115 DOI: 10.1038/s41467-018-03420-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Supraglacial lakes on the Greenland Ice Sheet are expanding inland, but the impact on ice flow is equivocal because interior surface conditions may preclude the transfer of surface water to the bed. Here we use a well-constrained 3D model to demonstrate that supraglacial lakes in Greenland drain when tensile-stress perturbations propagate fractures in areas where fractures are normally absent or closed. These melt-induced perturbations escalate when lakes as far as 80 km apart form expansive networks and drain in rapid succession. The result is a tensile shock that establishes new surface-to-bed hydraulic pathways in areas where crevasses transiently open. We show evidence for open crevasses 135 km inland from the ice margin, which is much farther inland than previously considered possible. We hypothesise that inland expansion of lakes will deliver water and heat to isolated regions of the ice sheet’s interior where the impact on ice flow is potentially large. Lakes on the Greenland Ice Sheet transfer water to the bed when they drain, but the impact is unknown. Here, the authors use a 3D model to show that lakes drain when fractures form, causing a chain reaction in which cascading lake drainages extend inland and deliver water to previously isolated regions of the bed.
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Affiliation(s)
- Poul Christoffersen
- Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER, UK.
| | - Marion Bougamont
- Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER, UK
| | - Alun Hubbard
- Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology, The Arctic University of Norway, N-9037, Tromsø, Norway.,Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK
| | - Samuel H Doyle
- Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK
| | - Shane Grigsby
- Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO, 80309, USA
| | - Rickard Pettersson
- Department of Earth Sciences, Geocentrum, Villavägen 16, 752 36, Uppsala, Sweden
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Kulessa B, Hubbard AL, Booth AD, Bougamont M, Dow CF, Doyle SH, Christoffersen P, Lindbäck K, Pettersson R, Fitzpatrick AAW, Jones GA. Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow. SCIENCE ADVANCES 2017; 3:e1603071. [PMID: 28835915 PMCID: PMC5559208 DOI: 10.1126/sciadv.1603071] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 07/19/2017] [Indexed: 06/07/2023]
Abstract
The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.
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Affiliation(s)
- Bernd Kulessa
- Glaciology Group, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK
| | - Alun L. Hubbard
- Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT The Arctic University of Norway, 9037 Tromsø, Norway
- Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK
| | - Adam D. Booth
- Institute of Applied Geoscience, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | - Marion Bougamont
- Scott Polar Research Institute, Department of Geography, University of Cambridge, Cambridge CB2 1ER, UK
| | - Christine F. Dow
- Department of Geography and Environmental Management, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
| | - Samuel H. Doyle
- Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK
| | - Poul Christoffersen
- Scott Polar Research Institute, Department of Geography, University of Cambridge, Cambridge CB2 1ER, UK
| | | | - Rickard Pettersson
- Department of Earth Sciences, Uppsala Universitet, Villavägen 16, 752 36 Uppsala, Sweden
| | - Andrew A. W. Fitzpatrick
- Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK
| | - Glenn A. Jones
- Glaciology Group, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK
- Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK
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Abstract
Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution.
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Abstract
Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow 'elements' specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development.
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Affiliation(s)
- Gwenn E Flowers
- Department of Earth Sciences , Simon Fraser University, 8888 University Drive , Burnaby, British Columbia, Canada V5A 1S6
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Kyrke-Smith TM, Fowler AC. Subglacial swamps. Proc Math Phys Eng Sci 2014; 470:20140340. [PMID: 25383024 PMCID: PMC4197471 DOI: 10.1098/rspa.2014.0340] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 08/05/2014] [Indexed: 11/15/2022] Open
Abstract
The existence of both water and sediment at the bed of ice streams is well documented, but there is a lack of fundamental understanding about the mechanisms of ice, water and sediment interaction. We pose a model to describe subglacial water flow below ice sheets, in the presence of a deformable sediment layer. Water flows in a rough-bedded film; the ice is supported by larger clasts, but there is a millimetric water layer submerging the smaller particles. Partial differential equations describing the water film are derived from a description of the dynamics of ice, water and mobile sediment. We assume that sediment transport is possible, either as fluvial bedload, but more significantly by ice-driven shearing and by internal squeezing. This provides an instability mechanism for rivulet formation; in the model, downstream sediment transport is compensated by lateral squeezing of till towards the incipient streams. We show that the model predicts the formation of shallow, swamp-like streams, with a typical depth of the order of centimetres. The swamps are stable features, typically with a width of the order of tens to hundreds of metres.
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Affiliation(s)
- T M Kyrke-Smith
- Department of Earth Sciences , University of Oxford , Oxford, UK ; MACSI , University of Limerick , Limerick, Republic of Ireland
| | - A C Fowler
- OCIAM , University of Oxford , Oxford, UK ; MACSI , University of Limerick , Limerick, Republic of Ireland
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9
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Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed. Nat Commun 2014; 5:5052. [PMID: 25262753 DOI: 10.1038/ncomms6052] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Accepted: 08/21/2014] [Indexed: 11/08/2022] Open
Abstract
The dynamic response of the Greenland Ice Sheet (GrIS) depends on feedbacks between surface meltwater delivery to the subglacial environment and ice flow. Recent work has highlighted an important role of hydrological processes in regulating the ice flow, but models have so far overlooked the mechanical effect of soft basal sediment. Here we use a three-dimensional model to investigate hydrological controls on a GrIS soft-bedded region. Our results demonstrate that weakening and strengthening of subglacial sediment, associated with the seasonal delivery of surface meltwater to the bed, modulates ice flow consistent with observations. We propose that sedimentary control on ice flow is a viable alternative to existing models of evolving hydrological systems, and find a strong link between the annual flow stability, and the frequency of high meltwater discharge events. Consequently, the observed GrIS resilience to enhanced melt could be compromised if runoff variability increases further with future climate warming.
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Kyrke-Smith TM, Katz RF, Fowler AC. Subglacial hydrology and the formation of ice streams. Proc Math Phys Eng Sci 2014; 470:20130494. [PMID: 24399921 PMCID: PMC3857858 DOI: 10.1098/rspa.2013.0494] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2013] [Accepted: 10/09/2013] [Indexed: 11/28/2022] Open
Abstract
Antarctic ice streams are associated with pressurized subglacial meltwater but the role this water plays in the dynamics of the streams is not known. To address this, we present a model of subglacial water flow below ice sheets, and particularly below ice streams. The base-level flow is fed by subglacial melting and is presumed to take the form of a rough-bedded film, in which the ice is supported by larger clasts, but there is a millimetric water film which submerges the smaller particles. A model for the film is given by two coupled partial differential equations, representing mass conservation of water and ice closure. We assume that there is no sediment transport and solve for water film depth and effective pressure. This is coupled to a vertically integrated, higher order model for ice-sheet dynamics. If there is a sufficiently small amount of meltwater produced (e.g. if ice flux is low), the distributed film and ice sheet are stable, whereas for larger amounts of melt the ice–water system can become unstable, and ice streams form spontaneously as a consequence. We show that this can be explained in terms of a multi-valued sliding law, which arises from a simplified, one-dimensional analysis of the coupled model.
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Affiliation(s)
- T M Kyrke-Smith
- Department of Earth Sciences , University of Oxford , Oxford, UK
| | - R F Katz
- Department of Earth Sciences , University of Oxford , Oxford, UK
| | - A C Fowler
- OCIAM , University of Oxford , Oxford, UK ; MACSI , University of Limerick , Limerick, Ireland
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