Cross equator transport of 137Cs from North Pacific Ocean to South Pacific Ocean (BEAGLE2003 cruises)

The anthropogenic radionuclides such as Cs-137, Sr-90, Tc-99, I-129 and some transuranics are important tracers of transport and biogeochemical processes in the ocean. Cs-137, with a half-life of 30 years, 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 degrees S during the BEAGLE cruise in 2003, surface seawater (around 80 L) was collected a few meters below the ocean surface by a pumping system. Water column samples (from 5 to 20 L) were collected using a Rosette multisampling system and Niskin bottles. Cs-137 was separated from seawater samples using ammonium phosphomolybdate (AMP) and analysed for Cs-137 in low-level HPGe gamma-ray spectrometers. Results allowed to draw a detailed picture of the distribution of Cs-137 in the South Pacific Ocean along P6 line. A Cs-137 depth section was depicted from about 160 samples. Cs-137 concentrations in the subsurface layers ranged from 0.07 +/- 0.04 Bq m(-3) to 1.85 +/- 0.145 Bq m(-3), high in the Tasman Sea and very low in the eastern region where upwelling occurs. Water column inventories of Cs-137 from surface to 1000 dbar depth ranged from 270 +/- 104 to 1048 +/- 127 Bq m(-2). It was concluded that the source of higher Cs-137 concentration and inventories in the Tasman Sea was Cs-137 deposited in the mid latitude of the North Pacific Ocean and transported across the equator during four decades. (C) 2010 Elsevier Ltd. All rights reserved.