Through this MSC action, I propose to design, test, and apply new genetic proxies for reconstruction of past sea ice extent. Satellite observations show an abrupt decrease in the extent of seasonal sea ice and state-of-the-art projections point to a seasonally ice-free Arctic Ocean by mid-century. Predicting the full range of climate change impacts on the Earth system requires an understanding of past variability. Past sea ice information is, however, limited by the fact that sea ice leaves no direct fingerprint in the geological record. The identification of new reliable proxies for sea ice is one of the most important challenges facing paleoclimatology today. DNA from sea ice microalgae offers an exciting possibility, as the sea ice environment harbours an enormously diverse and highly specialized community of protists, including diatoms and dinoflagellates. Because only a small fraction of sea ice microalgae leave a microfossil imprint in marine sediments and many species are only identifiable by advanced microscopy techniques, one limitation is that molecular references are lacking for many potential DNA gene markers. To identify the potential proxies I will apply classical taxonomy and DNA metabarcoding to study the vertical export of microalgae in the spring, after sea ice melt. The potential of the new sea ice proxies will be tested and selected markers will be applied by exploring sedimentary ancient DNA preserved in marine sediments records from the Arctic.