PB-210-DERIVED CHRONOLOGY AND THE FLUXES OF PB-210 AND CS-137 ISOTOPES INTO CONTINENTAL-SHELF SEDIMENTS, EAST-CHUKCHI-SEA, ALASKAN ARCTIC

Eleven sediment cores and eight sediment trap samples from the continental shelf of the Eastern Chukchi Sea were analyzed for Pb-210, Cs-137, and Ra-226. In selected samples, the organic carbon content and stable carbon isotope ratios were also determined. The excess Pb-210 (Pb-210(xs)) concentrations in the 1-cm core tops are generally lower than those of surficial sediments of subarctic shelves and arctic lakes. The sediment inventory-derived depositional fluxes of Pb-210 vary between 0.09 and 0.38 dpm cm(-2) y(-1), with a mean of 0.18 dpm cm(-2) y(-1). The apparent mass sediment accumulation rates, which vary between 31 and 324 mg cm(-2) y(-1) with a mean value of 133 mg cm(-2) y(-1), are about an order of magnitude lower than the yearly particle flux obtained from the sediment trap experiments. This difference between the relatively long-term and short-term yearly accumulation rates is likely due to the occasional resuspension of fine particles in the continental shelf areas and their advective transport to sites other than their initial deposition. The sediment inventory of Cs-137 varied between 0.64 and 4.09 dpm cm(-2) with a mean of 2.18 dpm cm(-2). A comparison of this inventory with the expected fallout inventory of Cs-137 suggests that there had been no detectable input of Cs-137 to the study area from the former USSR nuclear dump sites.