Sedimentary fluxes of ⁹⁰Sr, ¹³⁷Cs, ^239,240Pu and ²¹⁰Pb in the East Sea (Sea of Japan)

Sediment cores collected from the deep basins of the East Sea (Sea of Japan) provide an ongoing and historical record of artificial radionuclides contamination into one of the most highly publicized radioactive waste dumping areas in the world ocean. The depth distributions of ⁹⁰Sr, ¹³⁷Cs and ^239,240Pu in sediment cores were investigated with the aid of ²¹⁰Pb-derived sediment accumulation and mixing rates in the deep basins of the East Sea (Sea of Japan). Five box core samples were collected from the northern Yamato Ridge, Korea Plateau, Ulleung and Japan Basins below 1000-m depth. Sediment inventories of ¹³⁷Cs and ^239,240Pu are inversely correlated with water depth and linearly correlated with sediment accumulation rates. The inventories of these nuclides are linearly correlated with the accumulation rates of organic carbon in sediments. The ²³⁸Pu/^239,240Pu activity ratios in sediments are 0.036±0.009 suggesting that most of the Pu to the study area is derived from the global fallout. The activity ratios of ^239,240Pu/¹³⁷Cs, and ⁹⁰Sr/¹³⁷Cs in bottom sediments are much lower than those of global fallout due to the differences of particle affinity and biological uptake of these nuclides. Sediment inventories of ⁹⁰Sr and ¹³⁷Cs constitute <4% of the anticipated inventories from the global fallout, while those of ^239,240Pu constitute 30-150% of the anticipated inventories from the global fallout. The residence time of the dissolved ^239,240Pu in the study area is estimated to be 200-400 years based on the sediment inventory and/or sediment accumulation rate, and water column inventory.