Plutonium isotopes in seas around the Korean Peninsula

^239+240Pu concentrations and ²⁴⁰Pu/²³⁹Pu 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. ^239+240Pu concentrations in surface waters ranged from 3.1 to 22.3 mBq m^-3 with higher concentrations in winter than in summer. ^239+240Pu concentrations in seawaters around the Korean Peninsula are greater than that in the western North Pacific. ²⁴⁰Pu/²³⁹Pu 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 ²⁴⁰Pu/²³⁹Pu 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 ²⁴⁰Pu/²³⁹Pu atom ratios than that of global fallout may be explained by the hypothesis that the earlier input signal of low ²⁴⁰Pu/²³⁹Pu atom ratio (0.18-0.19) of global fallout plutonium in seas adjacent to the Korean Peninsula is being gradually diluted by the high ²⁴⁰Pu/²³⁹Pu atom ratio plutonium transported from the tropical Pacific Proving Grounds via prevailing ocean current.