210Pb and 226Ra distributions in the Circumpolar waters

Abstract

210Pb and 226Ra profiles have been measured at five GEOSECS stations in the Circumpolar region. These profiles show that 226Ra is quite uniformly distributed throughout the Circumpolar region, with slightly lower activities in surface waters, while 210Pb varies with depth as well as location or area. There is a subsurface 210Pb maximum which matches the oxygen minimum in depth and roughly correlates with the temperature and salinity maxima. This 210Pb maximum has its highest concentrations in the Atlantic sector and appears to originate near the South Sandwich Islands northeast of the Weddell Sea. Concentrations in this maximum decrease toward the Indian Ocean sector and then become fairly constant along the easterly Circumpolar Current. Relative to 226Ra, the activity of 210Pb is deficient in the entire water column of the Circumpolar waters. The deficiency increases from the depth of the 210Pb maximum toward the bottom, and the 210Pb/ 226Ra activity ratio is lowest in the Antarctic Bottom Water, indicating a rapid removal of Pb by particulate scavenging in the bottom layer and/or a short mean residence time of the Antarctic Bottom Water in the Circumpolar region. 226Ra is essentially linearly correlated with silica and barium in the Circumpolar waters. However, close examination of the vertical profiles reveals that Ba and Si are more variable than 226Ra in this region.