Late Pleistocene and Holocene sediments around South Georgia: archives for climate-induced signals in sub-Antarctica since the last glaciation

Abstract

The island of South Georgia, along with a number of other smaller islands, is part of a microcontinent surrounded by oceanic crust in the Atlantic sector of the sub-Antarctic. Oceanographically, South Georgia lies within the Antarctic Circumpolar Current (ACC), the broad oceanic current system that is driven by the Southern Hemisphere Westerlies (SHW) and climatically isolates the Antarctic continent from the warmer Northern Hemisphere. Its location in the middle of the ACC and its isolation from continental influences makes South Georgia a sensitive region, where climate changes are registered earlier than on the more thermally isolated Antarctic continent. So far, however, the timing and extent of the Last Glacial Maximum on South Georgia have not been completely resolved, mostly because radiocarbon dated sediment investigations are missing. This is mainly due to the lack of marine geological studies on the continental shelf of the southern side of the island, which is climatically much harsher and therefore less accessible than the northern side. This information, however, is important to create and evaluate reliable climate and ice sheet models. This thesis, based on the investigations of sediment cores, sediment echosounder profiles and high-resolution bathymetry data, closes important knowledge gaps in the King Haakon Trough System and Drygalski Fjord System on the southern shelf of South Georgia. For the latter, the radiocarbon-dated sediments reveal an extensive ice cap before 30 ka BP during the Local Last Glacial Maximum. In the King Haakon Trough System, the bathymetric and sediment echo-graphic mapping of this thesis also reveal shelf-wide glaciation, possibly related to the last glacial period. Furthermore, this thesis investigates the subsequent deglaciation and the traces left by climate variability and its drivers within the sedimentary records in the two cross-shelf troughs. The results show that the southern shelf environments were ice-free since before the Antarctic Cold Reversal and thus exposed to currents at least since the start of the Holocene. These likely reacted to climate fluctuations of the present interglacial and, therefore, impacted trough sedimentation. Thus, this thesis does not only provide evidence for past ice-extent, which is crucial for benchmarking modelling approaches, but also gives further insight into the Holocene climate variability and sedimentary processes around South Georgia, potentially even archiving shelf-intruding behaviour of the nearby Southern Antarctic Circumpolar Current Front (SACCF) for at least the last 8 ka BP.