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

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

Testing models of ice cap extent, South Georgia, sub-Antarctic

“…Our model results suggests that deglaciation on South Georgia occurred ca. 15 ka, which fits with geomorphological data from the east Antarctic Peninsula where initial retreat was underway by ~18-17.5 ka (Bentley et al, 2014), as 19 well as dates of the onset of peat formation and lake sedimentation at other sub-Antarctic islands, including Kerguelen, Auckland and Campbell, around this time (Hodgson et al, 2014b). …”

“…If a large LGM ice cap existed in South Georgia then there is potential for the same to have occurred on other sub-Antarctic islands within a similar climatic context e.g. Kerguelen, and also fits with other models of extensive LGM ice proposed for Heard, Bouvet and the South Orkney Islands (Hodgson et al, 2014b). The presence of an extensive LGM ice cap that reached the continental shelf edge around South Georgia suggests affinity with West Antarctica and the Antarctica Peninsula, which also experienced the most extensive glaciation at the LGM, rather than with Patagonia where the greatest glacial extents were earlier in the Quaternary (Darvill et al, 2015).…”

“…Though limited in size, the extent of glaciations of the sub-Antarctic islands, such as South Georgia, is of considerable interest due to their position in the Southern Ocean, providing a potential link between the climates of South America and West Antarctica (Hall, 2009;Hodgson et al, 2014a;2014b). Moreover, the extent of ice has important implications as to whether the sub-Antarctic islands acted as glacial refugia for biota (Barnes et al, 2006; Barnes et al, 2016;Hodgson et al, 2014b;Hogg et al, 2011; Thatje et al, 2008).…”

The Last Termination in the South Indian Ocean: A unique terrestrial record from Kerguelen Islands (49°S) situated within the Southern Hemisphere westerly belt

“…Nougier, 1970). In contrast, Hall (1984) suggested a more extensive ice-cover during the LGM with an equilibrium line altitude of c. 200 m. The timing of the last deglaciation is also not well known and is mainly based on a few basal radiocarbon dates of peat deposits (Hodgson et al, 2014;Van der Putten et al, 2010).…”

“…When sea level subsequently rose, peat deposits might have been eroded away. The interplay between eustatic and local sea level changes, however, is poorly constrained on Kerguelen Islands (Hodgson et al, 2014 and references there in). During fieldwork, it was observed that in front of the peat bank big rounded pebbles were present, probably representing an ancient beach level.…”