210Pb and 137Cs in margin sediments of the Arctic Ocean: Controls on boundary scavenging

Pb-210 and Cs-137 were measured in 25 sediment cores collected during the International Polar Year from a transect spanning the North American Arctic margin, from the North Bering Sea to Baffin Bay/Davis Strait. Profiles and inventories of the radioisotopes were used to determine sediment mixing and accumulation at each site and to assess the intensity of scavenging and burial. Sediment accumulation rates derived from Pb-210 and validated using Cs-137 are between <= 0.04 and 0.23 g cm(-2) yr(-1). Pb-210 cannot be used to derive sedimentation rates for vigorously biomixed sediments from the North Bering-Chukchi shelf. Elevated Cs-137 activities and inventories in recently deposited sediments imply delayed inputs of particle-associated Cs-137 to the sediments, likely transported from the watershed to the coast and subsequently redistributed to shelf/slope sediments. Inventories of Pb-210(ex) in all cores meet or exceed the estimated supply of Pb-210(ex) from atmospheric deposition and decay of Ra-226 in the water column. This implies that in contrast to the deep Arctic Ocean basin, there is a sufficient supply of suspended particulates along the North American Arctic margin to scavenge the supply of Pb-210(ex). Pb-210(ex) inventories in sediments are up to 21-fold greater than the in situ supply at some sites. Large inventories of Pb-210(ex) in sediments along the North Bering-Chukchi shelf result primarily from focusing, while those along the north Chukchi slope (Barrow Canyon) and in Baffin Bay/Davis Strait reflect strong boundary scavenging, likely supported by lateral exchanges with deep/interior Atlantic-origin waters.