Terrestrial and submarine evidence for the extent and timing of the Last Glacial Maximum and the onset of deglaciation on the maritime-Antarctic and sub-Antarctic islands

Dominic A Hodgson,Vincent Favier,William A Dickens,Michael J Bentley,Krystyna M Saunders,Eric A Colhoun,Elie Verleyen,Kevin Hall,Colm Ó Cofaigh,Vincent Jomelli,Daniel Brunstein,Andrew Mackintosh,Nathalie Van Der Putten,Werner Nel,Matt S Mcglone,Wim Vyverman,Roberts Sj ,David William Hedding ,P M Selkirk ,Alastair G C Graham ,Déborah Verfaillie ,James A Smith

doi:10.1016/j.quascirev.2013.12.001

Abstract

This paper is the maritime and sub–Antarctic contribution to the Scientific Committee for Antarctic Research (SCAR) Past Antarctic Ice Sheet Dynamics (PAIS) community Antarctic Ice Sheet reconstruction. The overarching aim for all sectors of Antarctica was to reconstruct the Last Glacial Maximum (LGM) ice sheet extent and thickness, and map the subsequent deglaciation in a series of 5000 year time slices. However, our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub–Antarctic sector. Therefore, in this paper we focus on an assessment of the terrestrial and offshore evidence for the LGM ice extent, establishing minimum ages for the onset of deglaciation, and separating evidence of deglaciation from LGM limits from those associated with later Holocene glacier fluctuations. Evidence included geomorphological descriptions of glacial landscapes, radiocarbon dated basal peat and lake sediment deposits, cosmogenic isotope ages of glacial features and molecular biological data. We propose a classification of the glacial history of the maritime and sub–Antarctic islands based on this assembled evidence. These include: (Type I) islands which accumulated little or no LGM ice; (Type II) islands with a limited LGM ice extent but evidence of extensive earlier continental shelf glaciations; (Type III) seamounts and volcanoes unlikely to have accumulated significant LGM ice cover; (Type IV) islands on shallow shelves with both terrestrial and submarine evidence of LGM (and/or earlier) ice expansion; (Type V) Islands north of the Antarctic Polar Front with terrestrial evidence of LGM ice expansion; and (Type VI) islands with no data. Finally, we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme.

Highlights

66 Reconstructing the Antarctic Ice Sheet through its Last Glacial Maximum (LGM) and post LGM deglacial history is important for a number of reasons
The minimum age of deglaciation of these cirques has not yet been determined, but chronological analyses of basal lake sediments in those occupied by tarns, or cosmogenic isotope analyses of moraines reported in some cirques, would provide this data. 227 The absence of widespread LGM glaciation at altitude is supported by cosmogenic isotope (10Be and 26Al) surface exposure dates on valley-axis and hillslope stone runs which range from 827,366 to 46,275 yr BP (Wilson et al, 2008, Table 2)
OSL dating of the sediments that underlie some stone runs suggest a period of enhanced periglacial activity between about 32,000 –27,000 yr BP, and confirms that parts of the stone runs may have been in existence from before 54,000 yr BP and so may substantially pre-date the LGM (Hansom et al, 2008). 237 Peat deposits as old as 40,521 – 41,705 cal yr BP have been found at Plaza Creek (Clark et al, 1998)

Summary

Introduction

66 Reconstructing the Antarctic Ice Sheet through its Last Glacial Maximum (LGM) and post LGM deglacial history is important for a number of reasons. The use of recent satellite gravity measurements (e.g. GRACE), and other geodetic data such as GPS, for ice sheet mass balance estimates requires an understanding of glacial–isostatic adjustment (GIA). A notable reconstruction has been that produced by Ivins and James (2005) which attempted to provide time-slices of the ice sheet from the LGM to the present-day to use as the basis of their GIA modelling. This ‘model’, termed IJ05, has been widely adopted by the satellite gravity and GPS communities as the ice sheet reconstruction with which to underpin their GIA assessments. Other sectors of the Antarctic Ice Sheet, including the maritime Antarctic islands west of the Antarctic Peninsula, are described elsewhere in this Special Issue. the combined volume of the maritime and sub-Antarctic LGM glaciers has had a very limited effect on global sea level, understanding past extent and timing of past glaciations in the sub-

Methods

Results

Discussion

Conclusion