New constraints on Greenland ice sheet dynamics during the last glacial cycle: evidence from the Uummannaq ice stream system

David H Roberts, Brice R Rea, Tim P Lane, Christopher Schnabel, Angel Rodés

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Abstract

This paper presents the first assessment of the Uummannaq ice stream system (UISS) in West Greenland. The UISS drained ~6% of the Greenland ice sheet (GrIS) at the Last Glacial Maximum (LGM). The onset of the UISS is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break. Mapping, cosmogenic radiogenic nuclide (CRN) dating, and model output reveal that glacially scoured surfaces up to 1266 m above sea level (asl) in fjord-head areas were produced by warm-based ice moving offshore during the LGM, with the elevation of warm-based ice dropping westwards to ~700 m asl as the ice stream trunk zone developed. Marginal plateaux with allochthonous blockfields suggest that warm-based ice produced till and erratics up to ~1200 m asl, but CRN ages and weathering pits suggest this was pre-LGM, with only cold-based ice operating during the LGM. Deglaciation began on the outer shelf at ~14.8 cal. kyrs B.P., with Ubekendt Ejland becoming ice free at ~12.4 ka. The UISS then collapsed with over 100 km of retreat by ~11.4 ka-10.8 cal. kyrs B.P., a rapid and complex response to bathymetric deepening, trough widening, and sea-level rise coinciding with rapidly increasing air temperatures and solar radiation, but which occurred prior to ocean warming at ~8.4 cal. kyrs B.P. Local fjord constriction temporarily stabilized the unzipped UISS margins at the start of the Holocene before ice retreat inland of the current margin at ~8.7 ka. Key Points Topograpy and geology control ice stream evolution Ice streams control regional landscape evolution through thermal partitioning Rapid deglaciation accelerated by bathymetric overdeepening + sea-level rise
Original languageEnglish
Pages (from-to)519-541
Number of pages23
JournalJournal of Geophysical Research: Earth Surface
Volume118
Issue number2
Early online date2 May 2013
DOIs
Publication statusPublished - Jun 2013

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ice stream
Greenland
Ice
Last Glacial
ice sheet
ice
cycles
Last Glacial Maximum
Sea level
fjord
sea level
deglaciation
trough
nuclides
ice retreat
landscape evolution
erratic
shelves
troughs
shelf break

Keywords

  • Greenland Ice Sheet
  • ice stream
  • landscape evolution

Cite this

New constraints on Greenland ice sheet dynamics during the last glacial cycle : evidence from the Uummannaq ice stream system. / Roberts, David H; Rea, Brice R; Lane, Tim P; Schnabel, Christopher; Rodés, Angel.

In: Journal of Geophysical Research: Earth Surface, Vol. 118, No. 2, 06.2013, p. 519-541.

Research output: Contribution to journalArticle

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N2 - This paper presents the first assessment of the Uummannaq ice stream system (UISS) in West Greenland. The UISS drained ~6% of the Greenland ice sheet (GrIS) at the Last Glacial Maximum (LGM). The onset of the UISS is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break. Mapping, cosmogenic radiogenic nuclide (CRN) dating, and model output reveal that glacially scoured surfaces up to 1266 m above sea level (asl) in fjord-head areas were produced by warm-based ice moving offshore during the LGM, with the elevation of warm-based ice dropping westwards to ~700 m asl as the ice stream trunk zone developed. Marginal plateaux with allochthonous blockfields suggest that warm-based ice produced till and erratics up to ~1200 m asl, but CRN ages and weathering pits suggest this was pre-LGM, with only cold-based ice operating during the LGM. Deglaciation began on the outer shelf at ~14.8 cal. kyrs B.P., with Ubekendt Ejland becoming ice free at ~12.4 ka. The UISS then collapsed with over 100 km of retreat by ~11.4 ka-10.8 cal. kyrs B.P., a rapid and complex response to bathymetric deepening, trough widening, and sea-level rise coinciding with rapidly increasing air temperatures and solar radiation, but which occurred prior to ocean warming at ~8.4 cal. kyrs B.P. Local fjord constriction temporarily stabilized the unzipped UISS margins at the start of the Holocene before ice retreat inland of the current margin at ~8.7 ka. Key Points Topograpy and geology control ice stream evolution Ice streams control regional landscape evolution through thermal partitioning Rapid deglaciation accelerated by bathymetric overdeepening + sea-level rise

AB - This paper presents the first assessment of the Uummannaq ice stream system (UISS) in West Greenland. The UISS drained ~6% of the Greenland ice sheet (GrIS) at the Last Glacial Maximum (LGM). The onset of the UISS is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break. Mapping, cosmogenic radiogenic nuclide (CRN) dating, and model output reveal that glacially scoured surfaces up to 1266 m above sea level (asl) in fjord-head areas were produced by warm-based ice moving offshore during the LGM, with the elevation of warm-based ice dropping westwards to ~700 m asl as the ice stream trunk zone developed. Marginal plateaux with allochthonous blockfields suggest that warm-based ice produced till and erratics up to ~1200 m asl, but CRN ages and weathering pits suggest this was pre-LGM, with only cold-based ice operating during the LGM. Deglaciation began on the outer shelf at ~14.8 cal. kyrs B.P., with Ubekendt Ejland becoming ice free at ~12.4 ka. The UISS then collapsed with over 100 km of retreat by ~11.4 ka-10.8 cal. kyrs B.P., a rapid and complex response to bathymetric deepening, trough widening, and sea-level rise coinciding with rapidly increasing air temperatures and solar radiation, but which occurred prior to ocean warming at ~8.4 cal. kyrs B.P. Local fjord constriction temporarily stabilized the unzipped UISS margins at the start of the Holocene before ice retreat inland of the current margin at ~8.7 ka. Key Points Topograpy and geology control ice stream evolution Ice streams control regional landscape evolution through thermal partitioning Rapid deglaciation accelerated by bathymetric overdeepening + sea-level rise

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