TESTING THE SUITABILITY OF THE CORALLINE ALGA CLATHROMORPHUM COMPACTUM AS A PROXY FOR PAST SEA ICE COVER IN THE ARCTIC

Summer sea ice extent is decreasing at a rate of -13.2 % per decade in the Arctic. This accelerated climate change is causing negative ecological repercussions on marine life and human livelihoods. Reliable cross-Arctic sea ice cover datasets are only available for the time period spanning the satellite record (since 1979). As such, it is important to reconstruct pre-satellite era environmental records to quantify the long-term rate of sea ice change in the Arctic and understand regional variability. It has recently been shown that the long lived coralline alga Clathromorphum compactum can record past sea ice information in its annual increment forming skeleton. During times of extensive sea ice cover little light reaches the seafloor resulting in low annual growth rates of the photosynthetic algae. In contrast, when sea ice cover is low annual algal growth rates increase. By measuring algal growth and geochemical composition year-by-year into the past, sea ice cover and temperatures can be reconstructed. C. compactum buildups are widespread throughout the entire Arctic where they can live for centuries attached to the shallow seafloor. Here we conducted sclerochronological and geochemical analyses of C. compactum to produce records of sea ice cover in the Central and Eastern Canadian Arctic, Greenland, and Svalbard. Algal time series were compared to observational sea ice records from 1979 to 2016 and other proxy data to test the strength of C. compactum as a sea ice cover proxy. Incremental magnesium to calcium (Mg/Ca) analysis along the axis of growth show annual cycles that help distinguish annual increment widths. Combined proxy data using Mg/Ca ratios and increment widths averaged from multiple samples at each collection site produced records for five sites. Results show significant correlations with annual regional summer sea ice concentration. Hence, with reported lifespans of >6 centuries, C. compactum can be used as an annual resolution in situ sea ice cover proxy throughout the Arctic.