Beschreibung: During expedition PS104 with RV Polarstern in February and March 2017 the MARUM MeBo 70 seabed drilling system was deployed at nine sites on the continental shelf of the Amundsen Sea Embayment, West Antarctica. A total of 57 meters of sediment core were recovered from 11 boreholes located in Pine Island Bay, Pine Island Trough, Bear Ridge and Cosgrove-Abbot Trough with recovery rates ranging from 7 to 76%. The main scientific objective of the drilling was to reconstruct the Late Mesozoic to Quaternary environmental history in this part of the Antarctic continental margin, with a special focus on the past dynamics of the marine based West Antarctic Ice Sheet (WAIS) from its inception to the last glacial cycle. Another main goal of the expedition was to test the suitability of the MeBo drill system for operating on the Antarctic continental shelf and recovering pre-glacial and glacially influenced sedimentary sequences. Here we will present the first results of sedimentological investigations carried out on the drill cores. These comprise (i) visual lithological descriptions, (ii) CT-scanning records of core stratigraphy, sedimentary structures, and possible artefacts induced by the drilling process, (iii) measurements of physical properties performed with a multi-sensor core logger, and (iv) characterisation of the geochemical composition of the drilled sedimentary strata using X-ray fluorescence (XRF) scanner data. Preliminary biostratigraphic investigations conducted on board ship indicated that the recovered sedimentary strata were deposited during various time slices spanning from the Late Cretaceous–Palaeocene to the Late Quaternary. We will provide an update of these initial chronological findings. Keywords: Drill cores, shelf sediments, West Antarctic Ice Sheet.

Beschreibung: The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological timescales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennialscale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.