Coralline algae as novel archive to decipher past North Atlantic/Arctic sea-ice cover and water temperature dynamics: climate trends and decadal variability

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In recent decades northern North Atlantic climate and ocean variability have experienced rapidly changing conditions, including accelerated decline in arctic sea-ice cover, substantial oceanic freshening trends, and drastic changes on the margins of Greenland's major ice sheets linked to ocean warming. Most prominent surface warming occurred in the northeastern Canadian Arctic and Greenland. These trends have already started altering ecosystems as well as human behaviour and may even influence the large-scale atmospheric circulation beyond the Arctic. However, climate models have not only failed to predict speed and extent of the observed Arctic sea-ice decline, but they also significantly underestimate recent surface warming. The major reason is lack of data. Hence the exploration of high-resolution marine archives from the extratropics will provide a perspective to reconstruct long-term climatic trends and variability, and in turn will improve climate models. The proposal will focus on encrusting coralline algae, marine plants growing attached to the seafloor, as novel climate recorders. Coralline algae have a multi-century lifespan and display clear annual growth bands, permitting sub-annually resolved reconstructions of paleoclimate. This project differs from all previous approaches in that: 1. For the first time a multicentury network of subannually-resolved paleo-records will be built from key sites, such as the Canadian Arctic, Greenland, and Spitsbergen. 2. Long-lived coralline algae are explored to reconstruct the past dynamics of seawater temperature, seasonal duration of sea-ice and ice cover, as well as freshwater flux over the past decades to centuries, and potentially even millennium. 3. The combination of geochemical and growth proxies are the powerful tools to reconstruct past variability, detect large-scale climate patterns and quantify the impact of anthropogenic warming. 4. Regional patterns of variability will be studied and compared to other climate archives. 5. Finally, algal multiproxy reconstructions will be integrated with millennium-scale paleo-simulations to better understand atmosphere-ocean interactions. Since instrument-derived data in subarctic and arctic environments are scarce, these new records will directly contribute to an improved understanding of climate dynamics prior to and since the industrial revolution.