Temporal And Spatial Variation Of ¹³⁷Cs In Offshore China

In this paper,we collected and processed the experimental data of 137Cs in seawater and sediments from offshore China,analyzed the temporal and spatial variation of 137Cs inputed into offshore China,discussed their properties,sources and the oceanographic process,and compared them with some experimental results.The spatial afid temporal distribution of 137Cs in surface seawater and water column was obtained based on the experimental data of 137Cs in offshore seawater of China in the research literature:(1)According to the time variation of 137Cs in surface seawater,the input history of 137Cs is reproduced,and the source term of 137Cs in offshore China is discussed,and the migration rates of Bohai Sea,Yellow Sea,East China Sea,South China Sea and offshore China are calculated as 0.050,0.029,0.028,0.013 and 0.029 a-1,respectively.The effective half-lives of the environment were 9.50,13.33,13.59,19.25,13.33 a,respectively.The average length of stay was 20.00,34.48,35.71,76.92 and 34.48 a,respectively.(2)Based on the spatial variation of 137Cs in surface seawater,the oceanographic processes such as ocean circulation and runoff input are discussed.The average 137Cs specific activity corrected to 2020 in surface waters of Bohai Sea,Yellow Sea,East China Sea,South China Sea and offshore China is 0.53,0.75,0.64,1.06 and 0.75 Bq·m-3,respectively.(3)Based on the spatial distribution of 137Cs inventory in the water column,the sedimentary characteristics of 137Cs and the invasion of ocean currents in offshore China are discussed.The average 137Cs inventory in Bohai Sea,Yellow Sea,East China Sea,South China Sea and offshore China are 2.68,97.25,323.06,695.54 and 279.63 Bq·m-2,respectively.Based on the experimental data of 137Cs in the offshore sediment cores of China in the research literature and the Stack processing method,the time change of specific activity,time change of flux and inventory spatial change of 137Cs in the sediment cores are obtained.Based on the experimental data of 137Cs in the surface sediments of offshore China in the research literature,the spatial distribution of 137Cs in the surface sediments is obtained:(1)According to the time variation of specific activity and flux of 137Cs in sediment cores,the input history of 137Cs is reproduced,and the source term of 137Cs in offshore China is discussed.(2)Based on the spatial variation of 137Cs inventory in sediment cores,the properties of 137Cs in offshore China and the oceanographic processes such as ocean circulation and runoff input are discussed.The inventory corrected to sedimentation age of Bohai Sea,Yellow Sea,East China Sea,South China Sea and offshore China are 5003.24,6141.84,7412.68,1601.31 and 5899.53 Bq·m-2,respectively.The inventory corrected to 2020 of Bohai Sea,Yellow Sea,East China Sea,South China Sea and offshore China are 1878.41,2317.19,2890.28,561.48 and 2266.63 Bq·m-2,respectively.(3)Based on the spatial distribution of 137Cs in surface sediments,the properties of 137Cs and oceanographic processes such as ocean circulation and runoff input in offshore China are discussed.The average 137Cs specific activity corrected to 2020 in surface sediments from Bohai Sea,Yellow Sea,East China Sea,South China Sea and offshore China is 2.11,1.38,1.32,0.99 and 1.45 Bq·kg-1,respectively.The specific activity of 137Cs in the surface seawater and surface sediments of several sea areas in the East China Sea was measured.From north to south,the studied sea areas were the East China Sea offshore,the sea areas adjacent to Ningde Nuclear Power Station,the sea areas adjacent to Fuqing Nuclear Power Station,and the sea areas adjacent to Xiamen.The average specific activity of 137Cs in surface waters adjacent to Ningde,Fuqing and Xiamen was 1.44,1.31 and 1.25 Bq·m-3,respectively,decreasing in turn.The average 137Cs specific activity in surface sediments adjacent to Ningde,Fuqing and Xiamen was 1.92,0.78 and 0.58 Bq·kg-1,respectively,decreasing in turn.The average specific activity of 137Cs in the offshore surface sediments of the East China Sea is 0.72 Bq·kg-1.Based on the historical data in the above-mentioned research literature,regression analysis and time series analysis were used as mathematical tools to predict the activity of surface seawater and surface sediments in the offshore China in recent years,and some experimental results were compared with those in this paper.In this study,we collected 137Cs data including seawater and sediments to understand the spatiotemporal variation of 137Cs in the waters of China in more detail,clarify their properties,sources and trace oceanographic processes,and discuss their geochemical behavior.The data on 137Cs content and inventory also provide important background information for future risk assessment and biogeochemical study of 137Cs in offshore China.