Premium
New constraints on Greenland ice sheet dynamics during the last glacial cycle: Evidence from the Uummannaq ice stream system
Author(s) -
Roberts David H.,
Rea Brice R.,
Lane Tim P.,
Schnabel Christoph,
Rodés Angel
Publication year - 2013
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1002/jgrf.20032
Subject(s) - geology , ice sheet , deglaciation , fjord , oceanography , ice stream , last glacial maximum , arctic ice pack , sea ice , greenland ice sheet , antarctic sea ice , fast ice , ice shelf , holocene , cryosphere
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.