Abstract
The main introduction routes of 137Cs into the Pacific Ocean are worldwide global fallout from atmospheric nuclear weapons testing and close-in fallout from U. S. tests in the northern Marshall Islands. The 137Cs activities and inventories in the water columns have been well investigated in the North Pacific Ocean, however, investigations on vertical profiles of 137Cs activities and inventories have been limited in the South Pacific Ocean. The objectives of this study are to measure the 137Cs activities in water columns collected in the western South Pacific Ocean and to discuss the processes controlling the 137Cs inventory. The 137Cs activities ranged from 1.4 to 2.3 Bq/m3 over the depth interval 0 - 250 m and decreased exponentially from the subsurface to 1000 m depth. The total 137Cs inventories ranged from 850 Bq/m2 in the Coral Sea Basin to 1270 Bq/m2 in the South Fiji Basin. The 137Cs inventories were 1.9 - 4.5 times higher than that of the expected deposition density of atmospheric global fallout at the same latitude. The possible sources of excess 137Cs inventories might be attributable to both the inter-hemisphere dispersion of the atmospheric nuclear weapons testing 137Cs from the northern stratosphere to the southern one and its subsequent deposition, and water-bearing transport of 137Cs from the North Pacific Ocean to the South Pacific.
