Low 210Pb in the upper thermocline in the Canadian Basin: scavenge process over the Chukchi Sea

Pb-210 was measured during the 3rd Chinese National Arctic Research Expedition cruise to investigate its spatial pattern in the western Arctic Ocean, as well as its relation with the thermocline in the Canadian Basin. The specific activities varied from 0.04 to 2.72, < 0.013 to 4.37, and 0.1 to 4.85 Bq/m(3) for dissolved, particulate, and bulk Pb-210, respectively, corresponding to respective averages of 0.65, 0.43, and 1.08 Bq/m(3). In the Canadian Basin, the minimum Pb-210 activities occurred in the thermocline, which was characterized by low temperature of -1.52A degrees C and salinity of 33.1. Combining the spatial distribution of Pb-210 and hydrographical characteristics in the western Arctic Ocean, this scenario was ascribed to the effective scavenging of Pb-210 when the Pacific water flowed across the Chukchi Shelf. Quantitatively, this interpretation was supported by both the shorter residence times and higher scavenging efficiencies (SE) of dissolved Pb-210 over the Chukchi Shelf. The highest SE values were observed in the Herald Shoal and bottom waters over the slope.