Discharge of ice-rafted debris in the Amundsen Sea as recorder of past West Antarctic Ice Sheet dynamics during late Cenozoic super-warm periods

The marine-based West Antarctic Ice Sheet (WAIS) is currently subject to accelerated mass loss (Favier et al., 2014; Fox-Kemper et al., 2021; Jenkins et al., 2010; Meredith et al., 2019; Mouginot et al., 2014; Rignot et al., 2019, 2014) and it is assumed that parts of it will collapse entirely in the future (DeConto and Pollard, 2016; Garbe et al., 2020; Sutter et al., 2016), leading to significant global sea-level rise (Meredith et al., 2019). However, it remains unclear whether the current rapid changes are part of a natural cycle or already relate to human-induced climate change (Noble et al., 2020). Further, no reliable field data exist so far for answering the question if WAIS collapses happened in the past and under which conditions those were initiated. Therefore, marine sediment records from West Antarctica’s most dynamic sector – the Amundsen Sea Embayment (ASE) – are a valuable archive for such changes over past glacial-interglacial cycles (DeConto and Pollard, 2016; Feldmann and Levermann, 2015; Hillenbrand et al., 2009, 2002; Noble et al., 2020; Rignot et al., 2019, 2014; Teitler et al., 2015) and help evaluating those uncertainties in a long-term geological context. Moreover, a better understanding of past analogue time periods will help to better assess potential future climate scenarios by improving the predictive capability of numerical models. In this thesis, past discharge of ice-rafted debris (IRD) in marine sediment cores U1532A 3H and U1332C 2F and 6F retrieved during IODP Expedition 379 to the Amundsen Sea are analysed to identify WAIS dynamics during late Cenozoic super-warm periods. In a multi-proxy approach, the results are further compared to variations in magnetic susceptibility, grain sizes, total organic carbon (TOC) barium/ aluminium (Ba/Al) ratios and clay mineral compositions. For this, discrete samples were wetsieved, weighed, and the fine fraction further processed with the Atterberg method. Magnetic susceptibility and x-ray fluorescence (XRF) data, as well as Ba/Al ratios, TOC measurements, and clay mineral composition results were already available and used for this thesis to contextualize the grain-size data. Specific intervals of high IRD discharge have been detected throughout all cores. As all of those intervals occur during times previously identified as super-interglacials (Scherer et al., 2008; Teitler et al., 2015), it is proposed that the WAIS retreated significantly at these times. Based on the comparison with the other proxies, it is concluded that those times were not only characterized by strongly increased ice discharge from the continent but also by mostly sea-ice free conditions, indicating a relatively warm and productive surface ocean