Meridional distribution of Ra in the west pacific and the southern ocean surface waters.

During the 13 (1996-1997) and the 19 (2002-2003) Chinese National Antarctica Research Expeditions, we collected 60 discrete surface seawater samples along the cruise from the Chanjiang River (Yangtze) estuary (30°59′S, 122°26′E) through Taiwan Strait, the South China Sea, and the Eastern Indian Ocean to Prydz Bay, Antarctica (69°10′S, 74°30′E), and analyzed them for the Ra specific activity. The Ra specific activity of the Chanjiang River estuary surface water (3.15 Bq/m) was found to be the highest among all the surface samples because of the desorption of Ra from riverine particles. Between Chanjiang River estuary and 40°S, Ra specific activity was found to be relatively uniform with a mean value of 1.07 Bq/m ( n = 19, SD = 0.14), similar to that of the open ocean. From 40°S to 65°S, Ra specific activity increased intensively, then decreased moderately further southwards. Near the Antarctic shore, it increased again, to 2.31 Bq/m. This distribution was controlled by a combination of deep water upwelling, Southern Ocean fronts, water mixing and the continental Ra import. In Prydz Bay and the adjacent sea area, the mean Ra activity value was 2.26 Bq/m ( n = 31, SD = 0.28), with a relatively higher value outside of the bay and low Ra activity value in the center of the bay. This was consistent with the topography and hydrological setting of the bay. In addition, we extended the study area northward to the Arctic, by combining the published Ra dataset for surface water from the Bering Sea to the Japan Sea. We also discuss the Ra distribution of high latitude oceanic surface water and its mechanisms. [ABSTRACT FROM AUTHOR]