Sedimentation of particulate organic carbon on the Amundsen Shelf, Antarctica

Abstract

We examined the recent history of sedimentary organic carbon (SOC) accumulation on the western Amundsen Shelf, to help characterize the biological carbon pump in the Amundsen Sea, Antarctica. Vertical sedimentary profiles (in the upper 21-cm) of SOC content, radio- and stable-carbon isotopes were obtained at four locations in the western Amundsen Sea: near the shelf break, inside the polynya near the Dotson Ice Shelf, and at both the periphery and the center of the Amundsen Sea polynya. Profiles were representative not only of various distances from the coast, but also of various summertime sea ice conditions and bottom depths. The SOC content (up to 1.1%) and the radiocarbon content were distinctly higher at the periphery and at the center of the polynya than at the other sites. The SOC and ¹⁴C contents were generally consistent with the spatial distribution of primary productivity in the surface water. A linear SOC accumulation rate of about 1.0 g Cm^-2 yr^-1 was determined from the conventional ¹⁴C ages of bulk SOC below the surface mixed layer at the periphery and at the center of the polynya, for the time period of 3.1 - 4.7 kyr before present (BP). This linear SOC accumulation rate was about 20 times greater than the rates determined at the two other sites for the period of 4.6 - 15.7 kyr BP. Note that all values are for uncorrected 14C ages. At the center of the polynya, a sudden change in SOC accumulation rate was observed at about 16 cm depth, corresponding to 4.7 kyr BP, implying that changes (during this time period) in physical environments greatly affected primary production, SOC burial and/or supply of allochthonous particles to this site. The vertical distribution of ¹⁴C content in the sediments implies that aged organic matter, likely associated with resuspended sediments, was also being deposited inside the polynya, in addition to autochthonous biogenic particles. If our estimation of SOC accumulation is extrapolated to the western Amundsen Shelf between 110°W and 120°W, approximately 3×1010 g C yr^-1 is buried on the shelf, with ~90% of SOC accumulation occurring in the Amundsen Sea polynya