Spatiotemporal variations of 137Cs and 90Sr in the global ocean based on the historical data

The anthropogenic radionuclides such as caesium-137 (¹³⁷Cs), strontium-90 (⁹⁰Sr), ³H, ¹⁴C, and plutonium (Pu) were released into the global ocean as results with large scale weapon tests in the late 1950s and early 1960s. Because these anthropogenic radionuclides have been still existed in the ocean, it is necessary to investigate the behavior of these anthropogenic radionuclides due to investigate the effects of human health. In this study, the spatiotemporal variations in the ¹³⁷Cs and ⁹⁰Sr activity concentrations in global ocean surface seawater from 1956 to 2021 using the HAMGlobal2021: Historical Artificial radioactivity database in Marine environment, Global integrated version 2021. The global ocean was divided into 37 boxes. The 0.5-yr average value of ⁹⁰Sr in the northern North Atlantic Ocean and its marginal sea, decreased exponentially in 1970–2010, just before the F1NPS accident. Estimated apparent half residence time of ¹³⁷Cs and ⁹⁰Sr ranged from 4.1-34.1 years and 3.6-25.2 years, respectively. Considering that longer Tap occurs larger inflow and shorter Tap occurs larger outflows/smaller inflow of radionuclide from the upstream region, ¹³⁷Cs and ⁹⁰Sr were inflowed into the Eastern China Sea from the subtropical western North Pacific Ocean. Inflow of ⁹⁰Sr into the Sea of Japan from the Eastern China Sea were relatively smaller than those of ¹³⁷Cs. Although ⁹⁰Sr were decreased exponentially, these trends tended to be larger than those of ¹³⁷Cs, which was investigated by our previous study (Inomata and Aoyama, 2023). This might be caused by the different behavior of ⁹⁰Sr and ¹³⁷Cs such as particulate form for ⁹⁰Sr in the seawater.

 

Keywords: ⁹⁰Sr, ¹³⁷Cs, Database, surface seawater, global ocean

Reference: Inomata and Aoyama, Evaluating the transport of surface seawater from 1956 to 2021 using ¹³⁷Cs deposited in the global ocean as a chemical tracer. Earth Syst. Sci. Data, 15, 1969–2007, 2023.