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 Th-234 and Pb-210. The study was undertaken in order to evaluate carbon sequestration in shelf sediments for this biologically productive Arctic shelf sea. Th-234 was detected below the sediment surface at only 3 of 11 stations (VIII, XII, XVIII). At these stations, 234Th sediment-mixing coefficients ranged from I to 12 cm(2) yr(-1). Among all stations, Pb-210-derived mass sediment accumulation rates quantified below the depth of surface sediment mixing vary from 320 to 650gm(-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 (similar to 10cm depth). The resulting OrgC burial rates range from 3.7 to 8.5 gCm(-2)yr(-1). Rates are highest (> 7 gCm(-2)yr(-1)) in troughs (Hopen Trench and N. Kvitoya Trench) with an average for all other stations of 5.5 +/- 1.7gCm(-2)yr(-1). Burial rates are tightly coupled to mass sediment accumulation except in Hopen Trench where OrgC burial rates are high (7.5gCm(-2)yr(-1)) despite low mass accumulation (similar to 330gm(-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 modem 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. (C) 2008 Elsevier Ltd. All rights reserved.