Meridional distribution of 226Ra in the west Pacific and the Southern Ocean surface waters

During the 13(th) (1996-1997) and the 19(th) (2002-2003) Chinese National Antarctica Research Expeditions, we collected 60 discrete surface seawater samples along the cruise from the Chanjiang River (Yangtze) estuary (30 degrees 59'S, 122 degrees 26'E) through Taiwan Strait, the South China Sea, and the Eastern Indian Ocean to Prydz Bay, Antarctica (69 degrees 10'S, 74 degrees 30'E), and analyzed them for the Ra-226 specific activity. The Ra-226 specific activity of the Chanjiang River estuary surface water (3.15 Bq/m(3)) was found to be the highest among all the surface samples because of the desorption of Ra-226 from riverine particles. Between Chanjiang River estuary and 40 degrees S, Ra-226 specific activity was found to be relatively uniform with a mean value of 1.07 Bq/m(3) (n = 19, SD = 0.14), similar to that of the open ocean. From 40 degrees S to 65 degrees S, Ra-226 specific activity increased intensively, then decreased moderately further southwards. Near the Antarctic shore, it increased again, to 2.31 Bq/m(3). This distribution was controlled by a combination of deep water upwelling, Southern Ocean fronts, water mixing and the continental Ra-226 import. In Prydz Bay and the adjacent sea area, the mean Ra-226 activity value was 2.26 Bq/m(3) (n = 31, SD = 0.28), with a relatively higher value outside of the bay and low Ra-226 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-226 dataset for surface water from the Bering Sea to the Japan Sea. We also discuss the Ra-226 distribution of high latitude oceanic surface water and its mechanisms.