| Summary: | Due to the nuclear testing in the 20th century, a considerable amount of anthropogenic transuranic isotopes ( 237 Np, 239, 240 Pu, and 241 Am) was produced, spread, and deposited in the natural environment including Antarctica. Here, activities of 239+240 Pu, 237 Np, and 241 Am in Antarctic marine sediments are determined by ICP-SF-MS, ranging from 0.008 to 0.293 Bq/kg for 239+240 Pu, from 0.057 to 0.926 mBq/kg for 237 Np, and from 0.027 to 0.277 Bq/kg for 241 Am. The dominant source of 237 Np, 239, 240 Pu, and 241 Am in the study marine sediments is global fallout. 240 Pu/ 239 Pu atom ratio is measured to be 0.179 ± 0.010 ( n = 17) on average, which is consistent with the global fallout of the nuclear weapons tests. Average 237 Np/ 239 Pu atom ratio for global fallout is suggested as 0.221 ( n = 58), which may be used as a new characteristic index to indicate the current source of Np in a certain region. Due to the different fractionations of Pu and Am by seawater and the enrichment efficiency of marine particles, 241 Am/ 239+240 Pu activity ratios in these samples (mean, 2.037 ± 0.040; n = 17) are much higher than global fallout. In addition, 237 Np/ 239 Pu atom ratio and 241 Am/ 239+240 Pu activity ratio are found to be positively correlated with the sampling depth. Furthermore, the correlation between organic matter and eight heavy metals with transuranic activities is revealed. The cold climate, latitude, and sediment properties have an important influence on the distributions of Np, Pu, and Am in these marine sediments of Antarctic.
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