Long term behaviour of 137Cs in the global marine environment: observations and model simulations

137Cs concentration surface water time series in 12 latitudinal boxes of the Pacific Ocean are re-investigated for the period from 1970 to 2005. The apparent half-residence times of 137Cs ranged from 11 to 36 years, depending on the position of the box. Generally these revised estimations of the apparent half-residence times are in good agreement with previous estimations. However, in a few boxes in the South Pacific we found longer apparent half-residence times. 137Cs inventories in the water column of the Pacific were also re-investigated for the period from 1970 to 2003. They are much smaller in the north of the subtropical gyre, however, they showed a less decrease in the south edge of the subtropical gyre. In the equatorial areas, 137Cs inventories had increased or been maintained constant. The main processes of these differences are caused by the southward transport of water masses due to subduction, and due to the existence of mid-depth minima at 300-400 m layers which correspond to the central mode water. (author)