Dramatic changes in sea ice have been observed in both poles in recent decades. However, the observational period for sea ice is short, and the climate models tasked with predicting future change in sea ice struggle to capture the current Antarctic trends. Paleoclimate archives, from marine sedimentary records and coastal Antarctic ice cores, provide a means of understanding sea ice variability and its drivers over decadal to centennial timescales. In this study, we collate published records of Antarctic sea ice over the past 2000 years (2 ka). We evaluate the current proxies and explore the potential of combining marine and ice core records to produce multi-archive reconstructions. Despite identifying 92 sea ice reconstructions, the spatial and temporal resolution is only sufficient to reconstruct circum-Antarctic sea ice during the 20th century, not the full 2 ka. Our synthesis reveals a 90 year trend of increasing sea ice in the Ross Sea and declining sea ice in the Bellingshausen, comparable with observed trends since 1979. Reconstructions in the Weddell Sea, the Western Pacific and the Indian Ocean reveal small negative trends in sea ice during the 20th century (1900–1990), in contrast to the observed sea ice expansion in these regions since 1979.

Reconstructing past hydrological and biogeochemical cycles, as well as sea ice variability in the Southern Ocean—especially along the Antarctic margin—relies on several micropaleontological, inorganic, and organic geochemical proxies preserved in marine sediments that have been developed and validated. However, robust local and regional calibrations for most of these paleoproxies, across the water column and in sediments, are still lacking when compared to present-day conditions and observations, hindering the quantification of past environmental variability. ICEPRO aims to address this gap by enhancing our understanding of past ocean-ice-earth interactions, linking modern observations with paleo-records through transnational collaborations on (paleo)environmental studies in the Southern Ocean. To achieve this goal, ICEPRO brings together international partners from diverse research disciplines (e.g., (paleo)climatologists, (paleo)oceanographers, biologists, and modelers) to coordinate and harmonize joint research activities, including sampling strategies, methodologies, proxy calibrations, and the planning of future Antarctic expeditions. Here, we present the main activities of ICEPRO.