The decline in sea ice is one of the most prominent features of climate change. Besides the discussions on the ecological effects of the ice-loss, a high focus is on the associated feedback mechanisms within the global climate system. Sea ice is not only highly responsive to climate change, it also has a strong impact on it. The major goal of the Helmholtz Young Investigator Group PALICE is to investigate changes in polar sea ice cover and associated shifts in oceanic and atmospheric circulation patterns during past climate fluctuations. Reliable and primarily quantitative indicators (proxies) to reconstruct sea ice conditions and ocean temperatures in the polar latitudes are, however, missing yet. The development of these urgently needed proxies and their systematic application for studying marine sediment cores from the Antarctic are a key aspect of our research. In close cooperation with the University of Bremen and the MARUM, these geological studies are accompanied by modelling approaches, which permit uncertainty estimates and hypothesis testing.