Sea-ice dynamics along West Antarctic continental shelves from the last deglacial to the Holocene - A multi-proxy biomarker approach

After experiencing three record-breaking low sea-ice summers in a course of seven years, Antarctic sea ice prompts a gaining interest among climate researchers. It is now more important than ever to get the best possible understanding of past Antarctic sea-ice behavior and its response to long- and short-term atmospheric and oceanographic changes on regional and pan-Antarctic scales. The knowledge as well as newly collected data will improve model simulations that aim to predict the future development of this climate-sensitive feature. Therefore, the need for tools that allow consistent and reliable paleo-reconstructions of Southern Ocean sea ice is high. The recently introduced organic sea-ice biomarker proxy IPSO25 has the potential to fulfill this need, however, thorough assessments of its applicability hitherto are sparse. A suite of sediment samples from West Antarctic continental shelves, which are affected most by strongly negative sea-ice trends, were investigated within this thesis to evaluate the proxy’s potential to display the recent and past sea-ice coverage in the study areas.
A study on seafloor surface sediments from the West Antarctic Peninsula, the Amundsen and Weddell seas demonstrated that the IPSO25 concentrations within the sediments do not adequately reflect the recent sea-ice conditions derived from satellite and numerical model data. For a semi-quantitative estimation of the sea-ice cover, IPSO25 was combined with a phytoplankton marker, resulting in the sea-ice index PIPSO25 (analogous to the sea-ice index IP25 for the Arctic), that allows are more realistic estimate of sea-ice coverage and hence seems to be a more suitable tool for paleo sea- ice reconstructions. To gather more information on ocean temperature, measurements of isoprenoidal glycerol dialkyl glycerol tetraethers were carried out and compared to instrument measurements of sea surface and subsurface temperatures, revealing the general capability of the proxy to mirror ocean temperatures.
In a further study, the applicability of IPSO25 alongside phytoplankton biomarkers, the sea-ice index PIPSO25, sedimentological parameters and physical properties was further investigated by means of a high-resolution sediment core located in the direct vicinity of the Pine Island Glacier in the eastern Amundsen Sea Embayment. Here, the multi-proxy dataset revealed the evolution from a polynya setting towards a more sea- ice dominated regime during the early Holocene and a following build-up of a heavy sea-ice cover. Potential interconnections between the regional sea-ice conditions and the inflow of Circumpolar Deep Water onto the continental shelf were drawn and discussed. For the third study as part of this thesis, IPSO25, phytoplankton biomarkers, the sea- ice index PIPSO25 and sedimentological proxies were used for sea-ice reconstructions in the western Amundsen Sea and compared to winter sea ice-estimates based on diatom assemblages. The multi-proxy dataset documents the waxing and waning of the Getz Ice Shelf since the last deglaciation. The first break-up of the Getz Ice Shelf around 13 cal. ka BP and the establishment of a sea-ice cover was followed by a phase of significantly reduced sea-ice cover at around 12.7 cal. ka BP until a re-expansion of sea ice occurred throughout the Holocene. These developments were linked to interhemispheric climate
patterns.
Regarding the new findings collected within this thesis, IPSO25 and the PIPSO25
approach can be considered a promising tool for (paleo) sea-ice reconstructions on the continental shelves off West Antarctica when interpreted carefully and alongside other paleoenvironmental parameters.