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Smith HJ, Dieser M, McKnight DM, SanClements MD, Foreman CM. Relationship between dissolved organic matter quality and microbial community composition across polar glacial environments. FEMS Microbiol Ecol 2018; 94:4995909. [DOI: 10.1093/femsec/fiy090] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Accepted: 05/11/2018] [Indexed: 11/12/2022] Open
Affiliation(s)
- HJ Smith
- Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, USA
| | - M Dieser
- Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, USA
- Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717, USA
| | - DM McKnight
- INSTAAR, University of Colorado Boulder, Boulder, CO 80303, USA
| | - MD SanClements
- INSTAAR, University of Colorado Boulder, Boulder, CO 80303, USA
- National Ecological Observatory Network, Boulder, CO 80301, USA
| | - CM Foreman
- Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, USA
- Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717, USA
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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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Flow Routing for Delineating Supraglacial Meltwater Channel Networks. REMOTE SENSING 2016. [DOI: 10.3390/rs8120988] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Dow CF, Kulessa B, Rutt IC, Tsai VC, Pimentel S, Doyle SH, van As D, Lindbäck K, Pettersson R, Jones GA, Hubbard A. Modeling of subglacial hydrological development following rapid supraglacial lake drainage. JOURNAL OF GEOPHYSICAL RESEARCH. EARTH SURFACE 2015; 120:1127-1147. [PMID: 26640746 PMCID: PMC4662019 DOI: 10.1002/2014jf003333] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Accepted: 05/08/2015] [Indexed: 06/05/2023]
Abstract
The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections. KEY POINTS Model for subglacial hydrological analysis of rapid lake drainage eventsLimited subglacial channel growth during and following rapid lake drainagePersistence of distributed drainage in inland areas where channel growth is limited.
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Affiliation(s)
- C F Dow
- Glaciology Group, College of Science, Swansea University Swansea, UK ; Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center Greenbelt, Maryland, USA
| | - B Kulessa
- Glaciology Group, College of Science, Swansea University Swansea, UK
| | - I C Rutt
- Glaciology Group, College of Science, Swansea University Swansea, UK
| | - V C Tsai
- Seismological Laboratory, California Institute of Technology Pasadena, California, USA
| | - S Pimentel
- Faculty of Natural and Applied Sciences, Department of Mathematics, Trinity Western University Langley, British Columbia, Canada
| | - S H Doyle
- Institute of Geography and Earth Sciences, Aberystwyth University Aberystwyth, UK
| | - D van As
- Geological Survey of Denmark and Greenland Copenhagen, Denmark
| | - K Lindbäck
- Department of Earth Sciences, Uppsala University Uppsala, Sweden
| | - R Pettersson
- Department of Earth Sciences, Uppsala University Uppsala, Sweden
| | - G A Jones
- Glaciology Group, College of Science, Swansea University Swansea, UK
| | - A Hubbard
- Institute of Geography and Earth Sciences, Aberystwyth University Aberystwyth, UK
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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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Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet. Proc Natl Acad Sci U S A 2015; 112:1001-6. [PMID: 25583477 DOI: 10.1073/pnas.1413024112] [Citation(s) in RCA: 134] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km(2) of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54-2.81 cm⋅d(-1)) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41-98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056-0.112 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅d(-1)), and when integrated over the melt season, totaled just 37-75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.
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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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