The deglacial history of southeast sector of the Greenland Ice Sheet during the Last Glacial Maximum

Roberts, D.H., Long, A.J., Schnabel, C., Freeman, S.P.H.T. and Simpson, M.J.R. (2008) The deglacial history of southeast sector of the Greenland Ice Sheet during the Last Glacial Maximum. Quaternary Science Reviews, 27(15-16), pp. 1505-1516. (doi:10.1016/j.quascirev.2008.04.008)

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Publisher's URL: http://dx.doi.org/10.1016/j.quascirev.2008.04.008

Abstract

The southeast sector of the Greenland Ice Sheet is currently experiencing rapid changes in mass balance and ice sheet dynamics at low elevations. However, to what extent these changes are typical of the behaviour of this sector of the ice sheet is uncertain, as our understanding of the longer-term controls on ice sheet dynamics in this region is limited. Two models exist for Last Glacial Maximum (LGM) ice sheet configuration in east Greenland. The first “minimum” model envisages a restricted ice sheet, with exposed nunataks in coastal areas and limited ice extent onto the continental shelf fed by ice flowing through bedrock troughs. A second, “maximum” model entails a thicker ice sheet with limited coastal nunataks, and ice filling the coastal valleys and extending across the entire continental shelf. Radiocarbon dates on foraminifera collected from seabed cores on the southeast Greenland continental shelf suggest that the ice sheet reached a maximum extent at ca 22 kcal. yr, before retreating, perhaps as early as ca 17 kcal. yr BP, and reaching the present coast at ca 10 kcal. yr BP. This paper presents the results of a study designed to test these different ice sheet models based on geomorphological mapping and cosmogenic isotope analyses in the Torqulertivit Imiat valley, an area to the east of the coastal town of Ammassalik. 26Al and 10Be measurements on abraded bedrock surfaces in terrain above local trimlines yield surface exposure ages of ca 11.8–9.9 ka. This demonstrates warm-based glacial erosion of high level surfaces (ca 740 m asl), followed by trimline formation during deglaciation and intense postglacial weathering. Our work constrains minimum ice thickness during the LGM to at least 740 m and supports a “maximum” ice sheet model in this sector of the GIS. Ice sheet retreat from the continental shelf to the southern edge of Sermilik Fjord is dated to ca 11.1–9.7 ka and helps to constrain the timing of the early Holocene retreat of the Helheim Glacier ice stream. Within the Torqulertivit Imiat valley, age determinations from glacially abraded terrain above the local marine limit on the coast (11.1–9.7 ka) and those from 10 km up-valley (12.8–9.9 ka), suggest rapid surface ablation during these intervals, coincident with rapid atmospheric warming observed in the Greenland ice core records.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Freeman, Professor Stewart and Schnabel, Dr Christoph
Authors: Roberts, D.H., Long, A.J., Schnabel, C., Freeman, S.P.H.T., and Simpson, M.J.R.
Subjects:Q Science > QE Geology
G Geography. Anthropology. Recreation > GE Environmental Sciences
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Quaternary Science Reviews
ISSN:0277-3791

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