Abstract
To re-evaluate the total amount of the Cs-137 global fallout, we analyzed worldwide historical data of Cs-137 observations in rain, seawater, soil and ice core. Another objective is to re-construct of temporal and spatial variation of Cs-137 global fallout as a source term for simulation of Cs-137 in the ocean using OGCM. A grid size is set 10 degree latitude by 10 degree longitude considering distribution of available data. 77 data for seawater column inventory, 179 data for deposition, 492 data for soil inventory and 3 data for ice core inventory were available for this study, respectively. 157 of 324 grid data obtained from the observational data in the Northern Hemisphere. For the grids in which no observational data was available, we fill them using the relationship between the fallout amount and precipitation amount at the neighboring grids. This study shows that total amount of Cs-137 fallout as of Jan. 1970 becomes ca. 770 PBq which largely exceeds previously reported value of 545 PBq in UNSCERA2000. The higher fallout regions are observed at the regions of warm current systems in the Pacific and Atlantic Oceans where higher precipitation amount occurs and the grater air mass exchange between stratosphere and troposphere also occurs. This study shows that UNSCEAR report on the part of total amount of Cs-137 fallout should be revised.
