Plutonium isotopes in seas around the Korean Peninsula

Pu239+240 concentrations and Pu-240/Pu-239 atom ratios in coastal seas adjacent to the Korean Peninsula were determined, during the period 1999 to 2002, to assess the current distribution and to identify sources of Pu isotopes. Pu239+240 concentrations in surface waters ranged from 3.1 to 22.3 mBq m(-3) with higher concentrations in winter than in summer. Pu239+240 concentrations in seawaters around the Korean Peninsula are greater than that in the western North Pacific. Pu-240/Pu-239 atom ratios ranged from 0.18 to 0.33 with an average value of 0.25 +/- 0.03, which is significantly higher than the global fallout average. The Pu-240/Pu-239 atom ratios of the 2000 m deep entire water column in the south western part of the East Sea (Sea of Japan) was comparable to that observed in waters near Bikini Atoll. The higher Pu-240/Pu-239 atom ratios than that of global fallout may be explained by the hypothesis that the earlier input signal of low Pu-240/Pu-239 atom ratio (0.18-0.19) of global fallout plutonium in seas adjacent to the Korean Peninsula is being gradually diluted by the high Pu-240/Pu-239 atom ratio plutonium transported from the tropical Pacific Proving Grounds via prevailing ocean current. (C) 2003 Elsevier B.V. All rights reserved.