Southern Hemisphere Ocean Tracer Study (SHOTS): An overview and preliminary results

摘要

Approximately 900 seawater samples were collected in the subtropical gyres in the South Pacific, the South Atlantic and the South Indian Ocean in 2003-2004 during the BEAGLE2003 cruise. Preliminary results show that ~(137)Cs and ~(239,240)Pu concentrations in surface waters were comparable with those in the subtropical gyres in the North Pacific. The ~(137)Cs profile shows a smaller effect of subduction on water mass transport. The estimated ~(137)Cs inventory of 800 Bq m~(-2) is about a half of the inventory in the North Pacific at the same latitude. The ~(239,240)Pu concentration at sub-surface maximum is one order of magnitude lower than that observed in the North Pacific, which is a remarkable difference when compared with ~(137)Cs profiles. Measured ~(240)Pu/~(239)Pu atom ratios are 0.20-0.24, statistically not different from the global fallout ratio. The SHOTS collaboration will produce a comprehensive dataset on anthropogenic radionuclides in the Southern Ocean. The obtained results will contribute to better understanding of processes in the water column using radionuclides as tracers, and they will improve our knowledge of circulation processes in the ocean, important for better understanding of climate change.