Reconstruction of paleo sea ice and climate dynamics based on highly branched isoprenoids at the Western Antartic Peninsula

Abstract

In context of rapid environmental change, the investigation of vulnerable parts of the global climate system is the focus of recent research. The assessment of global interactions between a changing climate and Antarctic sea ice, especially at the rapidly warming Western Antarctic Peninsula (WAP), aims to improve climate and ice sheet modelling for future projections. For this, the reconstruction of past sea ice distribution provides crucial information to enhance the capability of climate models. The goal of this thesis is the evaluation of the novel organic sea ice biomarker IPSO25 (ice proxy for the Southern Ocean with 25 carbon atoms) and its application as a new tool for past sea ice reconstructions analogously to its counterpart IP25 in the Arctic Ocean. This organic biomarker is a source specific organic compound from sea ice algae and associated with Antarctic spring sea ice. Information about the significance and limitations of this sea ice biomarker is still sparse and shall be revealed by using surface and downcore marine sediments. Comparisons to independent data such as biomarkers for open marine conditions, diatom assemblages, satellites data, ice core and marine sediment records improve the precise assessment of IPSO25. The distribution and evaluation of IPSO25 with recent sea ice data is the topic of the first study (Part I). The multiproxy investigation of surface sediment samples from the Drake Passage and the WAP reveals a good agreement of IPSO25 with ecological diatom data and satellite sea ice observations. The implementation of a sea ice index from combined open marine and sea ice biomarkers – PIPSO25 – implies that this tool is promising for paleo sea ice studies. The following two investigations (Part II and III) cover the last 200 a and 17 ka BP, respectively, based on three short and one long sediment records, and highlight the regional significance of IPSO25. Evaluation of the relation to sea salt sodium, methanesulfonic acid, numerical model output and reconstructed atmospheric circulation patterns (El Nino Southern Oscillation, Southern Annular Mode and Southern Westerly Winds) reveals that IPSO25 and PIPSO25 more likely indicate seasonal and dynamic sea ice changes than sea ice quantities. The development of past sea ice during the deglaciation and the Holocene at the WAP shows a significant change in sea ice seasonality in agreement with past investigations. The influence of the El Nino Southern Oscillation, the Southern Annular Mode and the Southern Westerly Winds is evident in sea ice biomarker production pattern due to high variability and the latitudinal position of westerly winds at the WAP. This thesis provides new reference data for paleo sea ice studies and provides a first research approach in further application of IPSO25, PIPSO25 and paleo sea ice investigations in Antarctica and the Southern Ocean.