High Spatial Variability in Under-Ice Export Fluxes over the Chukchi Plateau in the Pacific Arctic Region

A large proportion of algal production and carbon export occurs after snowmelt and before ice melt in the Arctic Ocean. To determine the magnitude of under-ice export fluxes over the Chukchi Plateau (CP), a total of 25 sediment trap deployments were completed at two ice camps during the annual field survey of the Korean IBRV Araon in 2018: a first ice camp (CP1) conducted from August 17 to 19 and a second ice camp (CP2) conducted from August 20 to 22. Chlorophyll a (chl a) and particulate organic carbon (POC) fluxes were measured at 2, 5, 10 and 30 m under ice, and zooplankton collected in the sediment traps were enumerated and identified. Both chl a and POC fluxes were the highest at 5 m under ice at CP2, likely due to enhanced fluxes of the sea ice algae Melosira arctica and to a potential higher release of particulate matter from a thinner sea ice cover. Whereas Calanus glacialis/marshallae were dominant at all depths and both sites, the large numbers of individuals observed at 10 m at CP1 likely enhanced zooplankton grazing pressure at that site, further contributing to the high spatial variability in under-ice export fluxes. Overall, under-ice fluxes obtained in August 2018 highlighted the importance of M. arctica aggregates as a source of carbon for pelagic consumers and for carbon export during summer over the Chukchi Plateau.