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Bradwell T, Small D, Fabel D, Smedley RK, Clark CD, Saher MH, Callard SL, Chiverrell RC, Dove D, Moreton SG, Roberts DH, Duller GAT, Ó Cofaigh C. Ice-stream demise dynamically conditioned by trough shape and bed strength. Sci Adv 2019; 5:eaau1380. [PMID: 31058217 PMCID: PMC6498188 DOI: 10.1126/sciadv.aau1380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Accepted: 03/07/2019] [Indexed: 06/09/2023]
Abstract
Ice sheet mass loss is currently dominated by fast-flowing glaciers (ice streams) terminating in the ocean as ice shelves and resting on beds below sea level. The factors controlling ice-stream flow and retreat over longer time scales (>100 years), especially the role of three-dimensional bed shape and bed strength, remain major uncertainties. We focus on a former ice stream where trough shape and bed substrate are known, or can be defined, to reconstruct ice-stream retreat history and grounding-line movements over 15 millennia since the Last Glacial Maximum. We identify a major behavioral step change around 18,500 to 16,000 years ago-out of tune with external forcing factors-associated with the collapse of floating ice sectors and rapid ice-front retreat. We attribute this step change to a marked geological transition from a soft/weak bed to a hard/strong bed coincident with a change in trough geometry. Both these factors conditioned and ultimately hastened ice-stream demise.
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Affiliation(s)
- Tom Bradwell
- Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK
- British Geological Survey, The Lyell Centre, Edinburgh EH14 4AP, UK
| | - David Small
- Department of Geography and Planning, Durham University, Durham DH1 3LE, UK
| | - Derek Fabel
- Scottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 0QF, UK
| | - Rachel K. Smedley
- Department of Geography, University of Liverpool, Liverpool L69 3BX, UK
| | - Chris D. Clark
- Department of Geography, University of Sheffield, Sheffield S10 2TN, UK
| | - Margot H. Saher
- School of Ocean Sciences, Bangor University, Menai Bridge LL59 5AB, UK
| | - S. Louise Callard
- Department of Geography and Planning, Durham University, Durham DH1 3LE, UK
| | | | - Dayton Dove
- British Geological Survey, The Lyell Centre, Edinburgh EH14 4AP, UK
| | | | - David H. Roberts
- Department of Geography and Planning, Durham University, Durham DH1 3LE, UK
| | - Geoff A. T. Duller
- Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK
| | - Colm Ó Cofaigh
- Department of Geography and Planning, Durham University, Durham DH1 3LE, UK
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Ó Cofaigh C. Ice sheets viewed from the ocean: the contribution of marine science to understanding modern and past ice sheets. Philos Trans A Math Phys Eng Sci 2012; 370:5512-5539. [PMID: 23129711 DOI: 10.1098/rsta.2012.0398] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Over the last two decades, marine science, aided by technological advances in sediment coring, geophysical imaging and remotely operated submersibles, has played a major role in the investigation of contemporary and former ice sheets. Notable advances have been achieved with respect to reconstructing the extent and flow dynamics of the large polar ice sheets and their mid-latitude counterparts during the Quaternary from marine geophysical and geological records of landforms and sediments on glacier-influenced continental margins. Investigations of the deep-sea ice-rafted debris record have demonstrated that catastrophic collapse of large (10(5)-10(6) km(2)) ice-sheet drainage basins occurred on millennial and shorter time scales and had a major influence on oceanography. In the last few years, increasing emphasis has been placed on understanding physical processes at the ice-ocean interface, particularly at the grounding line, and on determining how these processes affect ice-sheet stability. This remains a major challenge, however, owing to the logistical constraints imposed by working in ice-infested polar waters and ice-shelf cavities. Furthermore, despite advances in reconstructing the Quaternary history of mid- and high-latitude ice sheets, major unanswered questions remain regarding West Antarctic ice-sheet stability, and the long-term offshore history of the East Antarctic and Greenland ice sheets remains poorly constrained. While these are major research frontiers in glaciology, and ones in which marine science has a pivotal role to play, realizing such future advances will require an integrated collaborative approach between oceanographers, glaciologists, marine geologists and numerical modellers.
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Ó Cofaigh C, Evans J, Dowdeswell JA, Larter RD. Till characteristics, genesis and transport beneath Antarctic paleo-ice streams. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006jf000606] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Ó Cofaigh C, Larter RD, Dowdeswell JA, Hillenbrand CD, Pudsey CJ, Evans J, Morris P. Flow of the West Antarctic Ice Sheet on the continental margin of the Bellingshausen Sea at the Last Glacial Maximum. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005jb003619] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Colm Ó Cofaigh
- Department of Geography; University of Durham; Durham UK
| | | | | | | | | | - Jeffrey Evans
- Scott Polar Research Institute; University of Cambridge; Cambridge UK
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Cofaigh CÓ, Taylor J, Dowdeswell JA, Rosell-Melé A, Kenyon NH, Evans J, Mienert J. Sediment reworking on high-latitude continental margins and its implications for palaeoceanographic studies: insights from the Norwegian-Greenland Sea. ACTA ACUST UNITED AC 2002. [DOI: 10.1144/gsl.sp.2002.203.01.17] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractGeological evidence indicates that sediment reworking is common around the continental margins and abyssal depths of the Norwegian-Greenland Sea, a high-latitude setting with glacier-influenced margins. Detailed analysis of 22 cores up to 5 m long, placed in context by accompanying geophysical data including high resolution sub-bottom profiles, swath bathymetry and backscatter maps, indicates that reworking is variable and ranges from debris flows and turbidity currents, to bottom-current activity, as well as iceberg scouring. Reworking by debris flows appears to be restricted mainly to the main trough-mouth fans and sediment slides. Elsewhere, turbidity-current activity frequently dominates, although iceberg ploughing down to 600 m depth and current winnowing assume increasing significance on continental shelves. Reworking in the Norwegian-Greenland Sea reflects variations in ice-sheet dynamics that, in turn, influence the rate of sediment delivery and location of depocentres. Spatial variations in the style of reworking may also reflect the influence of continental slope gradient and bedrock geology on continental shelves. The widespread nature of sediment reworking has important implications for palaeoceanographic investigations in the region, as reworking can result in erosion and disturbance of the sediment column. It is estimated that less than 7% of material delivered to the Norwegian-Greenland Sea since the Late Weichselian is derived from hemipelagic and pelagic sedimentation. This problem is significant where continuous, high-resolution records of hemipelagic and pelagic sedimentation are required, and attempts are made to correlate with other high-resolution proxy records, such as ice cores, at sub-millennial scales. Bioturbation results in the smoothing of high-resolution records and imposes a maximum resolution for sediment-core time-slices of generally 400 years or more. In the Norwegian-Greenland Sea, areas of high sedimentation such as trough-mouth fans or contourite drifts are commonly associated with extensive reworking. Identification of reworking is particularly important where attempts are made to link records of iceberg-rafted debris to past ice-sheet dynamics, as bottom-current winnowing and mass-flow processes can increase the concentration of coarse-grained iceberg-rafted debris. Such localized accentuation of the iceberg-rafted debris signal may lead to erroneous palaeo-environmental interpretations. It is therefore critical that palaeoceanographic interpretations are firmly underpinned by an explicit sedimentological assessment of reworking.
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Affiliation(s)
- Colm Ó Cofaigh
- Scott Polar Research Institute and Department of Geography, University of Cambridge Cambridge CB2 1ER, UK
| | - Justin Taylor
- Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol Bristol BS8 1SS, UK
| | - Julian A. Dowdeswell
- Scott Polar Research Institute and Department of Geography, University of Cambridge Cambridge CB2 1ER, UK
| | - Antoni Rosell-Melé
- ICREA, Centre of Environmental Studies, Universitat Autonoma de Barcalona 018193 Bellaterra, Catalonia, Spain
| | - Neil H. Kenyon
- Southampton Oceanography Centre European Way, Southampton SO14 3ZH, UK
| | - Jeffrey Evans
- British Antarctic Survey High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Jürgen Mienert
- Department of Geology, University of Tromsø Dramsveien 201, 9037 Tromsø, Norway
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