Utilization and Importance of Sea Ice Derived Organic Carbon to Benthic Communities of the Chukchi Sea: Evidence from Highly Branched Isoprenoid Biomarkers

Peak ice algal export in the northern Chukchi Sea typically occurs during the initiation of ice retreat in June and July. The presence of highly branched isoprenoid biomarkers in macrofaunal invertebrate communities collected during the seasonally ice-free period indicates utilization and/or storage of organic carbon linked to sympagic sources. Preferential uptake of sea ice organic carbon varied among different species and feeding strategies. These biomarkers were also observed in particle fluxes collected from the Chukchi Ecosystem Observatory moored sediment trap and surface sediment samples. These results confirm that ice algal compounds are present year round in the northeast Chukchi Sea, with maximum concentrations in July. This is likely from production during ice break up, as well as advection (spring/summer), resuspension (fall/winter), and production during ice formation. The presence of biomarkers suggests that following an ice algae bloom, the particles settle on the seafloor and are retained in the sediments through rapid burial of freshly deposited organic matter by bioturbation. The year round presence of sea ice organic carbon in the particle fluxes, stored in the sediments and in invertebrate tissue highlights the probable importance of ice algae in the Pacific Arctic ecosystem. The persistent storage of sea ice organic carbon may also help buffer the loss or redistribution of sea ice algae in the short term as seasonal sea ice continues to decline, supporting the concept of a sediment “food bank” as influenced by the retentive properties of the northeast Chukchi region driven by the physical current structure.