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Abstract: The 137Cs seawater transect along the 20°S latitude in the Indian Ocean, sampled during the round the globe BEAGLE2003 (Blue Ocean Global Expedition) clearly shows a presence of two cores of higher 137Cs concentrations at 100°E and 55°E in water column depths between 100 and 200m. The subsurface maximum of 137Cs activity concentration (2.1mBq/L) observed near 100°E is the highest level found in southern hemisphere seawater, which is comparable to the maximum 137Cs concentration observed in North Pacific surface water. This transect represents the first high density sight of 137Cs distribution in South Indian Ocean waters. The estimated 137Cs water column inventories (up to 1240Bq/m2), normalized for the 1000m water depth along the 20°S latitude are by a factor of three higher than would be expected from global fallout in the South Indian Ocean. The estimated residence time of 137Cs in surface waters of the South Indian Ocean (∼30years) is by about a factor of two higher than for the North Pacific. The 137Cs data confirm a transport of surface waters from the North Pacific via Indonesian seas to the South Indian Ocean, and to the subtropical gyre. The subtropical gyre is an important reservoir of anthropogenic pollutants that have been transported from the North Pacific and Indian Oceans to the south on a time-scale of several decades. [Copyright &y& Elsevier]

Abstract: The anthropogenic radionuclides such as 137Cs, 90Sr, 99Tc, 129I and some transuranics are important tracers of transport and biogeochemical processes in the ocean. 137Cs, with a half-life of 30years, a major fission product present in a dissolved form in seawater, is a good tracer of oceanic circulation at a time scale of several decades. At WOCE P6 line along 30°S during the BEAGLE cruise in 2003, surface seawater (around 80L) was collected a few meters below the ocean surface by a pumping system. Water column samples (from 5 to 20L) were collected using a Rosette multisampling system and Niskin bottles. 137Cs was separated from seawater samples using ammonium phosphomolybdate (AMP) and analysed for 137Cs in low-level HPGe gamma-ray spectrometers. Results allowed to draw a detailed picture of the distribution of 137Cs in the South Pacific Ocean along P6 line. A 137Cs depth section was depicted from about 160 samples. 137Cs concentrations in the subsurface layers ranged from 0.07±0.04Bqm−3 to 1.85±0.145Bqm−3, high in the Tasman Sea and very low in the eastern region where upwelling occurs. Water column inventories of 137Cs from surface to 1000dbar depth ranged from 270±104 to 1048±127Bqm−2. It was concluded that the source of higher 137Cs concentration and inventories in the Tasman Sea was 137Cs deposited in the mid latitude of the North Pacific Ocean and transported across the equator during four decades. [Copyright &y& Elsevier]

Abstract: During the reoccupation of the WOCE transect A10 at 30°S by the BEAGLE2003 cruise, the SHOTS project partners collected a large number of samples for the analysis of isotopic tracers. 137Cs was mostly deposited on the oceans surface during the late 1950s and early 1960s, after the atmospheric detonation of large nuclear devices, which mostly occurred in the Northern Hemisphere. The development of advanced radioanalytical and counting techniques allowed to obtain, for the first time in this region, a zonal section of 137Cs water concentrations, where little information existed before, thus constituting an important benchmark for further studies. 137Cs concentrations in the upper waters (0–1000m) of the south-eastern Atlantic Ocean are similar to those observed in the south-western Indian Ocean, suggesting transport of 137Cs labeled waters by the Agulhas current to the Benguela Current region. In contrast, bomb radiocarbon data do not show this feature, indicating the usefulness of 137Cs as a radiotracer of water mass transport from the Indian to the South Atlantic Ocean. [Copyright &y& Elsevier]