Accumulation of organic carbon in western Barents Sea sediments

Seafloor sediment dynamics operating in the western Barents Sea modulate the accumulation of particulate organic carbon on the shelf. As part of the CABANERA project, an integrated study of carbon dynamics in the marginal ice zone, we quantify burial rates of organic carbon (OrgC) at 11 sites. We further assess physical and biological mixing of surface sediments using the radionuclide tracers 234Th and 210Pb. The study was undertaken in order to evaluate carbon sequestration in shelf sediments for this biologically productive Arctic shelf sea. 234Th was detected below the sediment surface at only 3 of 11 stations (VIII, XII, XVIII). At these stations, 234Th sediment-mixing coefficients ranged from 1 to 12 cm2 yr−1. Among all stations, 210Pb-derived mass sediment accumulation rates quantified below the depth of surface sediment mixing vary from 320 to 650 g m−2 yr−1. With the exception of stations in Hopen Trench (OrgC=1.9–2.6%), sedimentary OrgC content ranges from 1.0% to 1.6%, decreasing only slightly from present-day (surface sediments) back to 1860 (∼10 cm depth). The resulting OrgC burial rates range from 3.7 to 8.5 g C m−2 yr−1. Rates are highest (>7 g C m−2 yr−1) in troughs (Hopen Trench and N. Kvitøya Trench) with an average for all other stations of 5.5±1.7 g C m−2 yr−1. Burial rates are tightly coupled to mass sediment accumulation except in Hopen Trench where OrgC burial rates are high (7.5 g C m−2 yr−1) despite low mass accumulation (∼330 g m−2 yr−1). Homogenization of surface sediments through mixing diminishes the time-scale of resolution for our derived carbon burial rates to 10–25 years. We find that modern sediments accumulating on the shelf represent on average 5–7% of the annual integrated pelagic primary production or 11–15% of the vertical flux for the Barents Sea.