Sinking particle flux in the sea ice zone of the Amundsen Shelf, Antarctica

Abstract

We have examined the flux, biogenic composition, and isotopic values of sinking particles collected by a time-series sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for one year. The major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to <60 %. Biogenic components, dominated by opal (~78 % of the biogenic components), accounted for over 75 % of particle flux during this high flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content (>30 %) and low bio-Si/POC ratio (<0.5) during the austral winter. CaCO3 content and its contribution to total particle flux were low (~6 %) throughout the study period. Aged POC likely supplied from sediment resuspension accounted for a considerable fraction only from October to December, which was evidenced by low radiocarbon content and relatively high (30-50 %) content of the non-biogenic component. When compared to POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical although maximum POC flux was about half that inside the Amundsen Sea polynya. This comparatively high POC flux integrated over the austral summer in the SIZ may be caused by persistence of phytoplankton bloom for a longer period and more efficient export of organic matter potentially owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen Shelf, the role of the SIZ compared to the polynyas need to be examined more carefully when trying to characterize the POC export in this region.