LATE PLEISTOCENE AND HOLOCENE GLACIATION AND CLIMATE HISTORY OF THE ANTARCTIC PENINSULA REGION - ACCORDING TO THE LAND AND LAKE SEDIMENT RECORD

Christian Hjort, Lund University
Quaternary Geology
Sölvegatan 13, SE-223 62 Lund, Sweden
E-mail:christian.hjort@geol.lu.se

High marine shorelines in the South Shetland Islands (>100 m above present sea level) and on islands in the northwestern Weddell Sea (c. 80 m a.s.l.) indicate former heavy glacio-isostatic depression of the land. In combination with the occurrence of glacially transported Antarctic Peninsula crystalline boulders at considerable altitudes, e.g. among the islands in the Weddell Sea, and with glacially reworked shell-bearing marine sediments aged well beyond the limit of ¹⁴C-dating, this indicates at least one rather late Pleistocene glacial event predating and outsizing the Last Global Glacial Maximum (LGM; marine isotope stage 2) in this region. This major advance has not yet been absolutely dated, but an early-middle Weichselian/Wisconsinan age might be suspected.

The LGM glaciation in the region may not have been as thick as usually anticipated, and perhaps it only reached a few hundred meters above present sea level in the lanes among the islands in the northwestern Weddell Sea. It did however increase in thickness southwards - as mirrored by the "post-glacial" (Holocene) marine limit rising from c. 30 m in the north (James Ross Island) to c. 55 m in the south (Marguerite Bay).

The deglaciation of the presently ice-free land areas was late compared with events in the Northern Hemisphere. It commenced in the South Shetlands around 10 000 cal.years BP, but otherwise mostly took place after 8500 BP and in some places was not completed until some 2500 years later. There are also indications of mid-Holocene glacial advances around 5000 BP, associated with marine levels between 10-15 m a.s.l.

The Holocene climatic optimum, as recorded on land, e.g. from lake sediment cores, lasted between c. 4500-3000 BP. It thus came much later than its equivalent in the Northern Hemisphere - but its timing is well in accordance with what might be expected from the regional insolation curve.

After 3000 BP the climate again became colder, with the beginning of the Neoglacial period, perhaps heralding the onset of the post-Holocene ice age. It temporarily culminated with glacial advances some hundred years ago, documented e.g. from the South Shetlands and roughly parallell in time with the Little Ice Age in the Northern Hemisphere.