Artificial radionuclides in the Yellow Sea: Inputs and redistribution

The Yellow Sea is one of the marginal seas of the Northwest Pacific receiving large amounts of material from the continent via rivers and atmosphere. In order to understand the sources and present levels of key artificial radionuclides (⁹⁰Sr, ¹³⁷C and ^239+240Pu) in the Yellow Sea, the processes affecting their distribution in the water column and their burial in the sea floor, their concentrations were determined in seawater and bottom sediment samples collected from the Yellow Sea during 1994-2000, and from the East China Sea and the tropical Northwest Pacific during 1993 and 1994. The atmospheric and riverine inputs were also assessed at the mid-eastern coast of the Yellow Sea. The atmospheric deposition of radionuclides appears to be dominated by the long-range transport from the arid regions of the Asian continent with the highest values during the spring Asian dust storms and lowest in the summer wet monsoon period. The dry atmospheric deposition flux appeared to be particularly important for ^239+240Pu. Riverine fluxes of radionuclides dominated the total input due to the sheer size of the riverine water and sediment fluxes into the sea. The river input was seen in their distribution in the surface of the sea, particularly for ⁹⁰Sr in winter. In summer, the water column stratification segregates these radionuclides vertically, so they are depleted in the surface layer and enriched in the bottom layer. The half-removal rate for ⁹⁰Sr and ¹³⁷Cs was estimated to be 7 years. The levels of radionuclides in the Yellow Sea were higher than in the adjacent seas, and significant amounts of them have been exported from the Yellow Sea to the adjacent seas.