Relationship between Tritium Concentration, Hydrogen and Oxygen of Stable Isotope Ratios, and Major Ion Components for Monthly Precipitation in Southwestern Part of Japan

Abstract

The aim of this study is to get a better understanding of the variation of tritium concentration for monthly precipitation collected at Okinawa Island, the southwestern part of Japan. Tritium concentrations of monthly precipitation in Okinawa from June 2014 to December 2019 ranged from 0.05 to 0.27 Bq L^–1. Seasonal patterns of tritium concentration are determined with higher in spring and lower in autumn. The results of δD and δ¹⁸O indicate that the tritium concentration in winter is affected by the dilution effect of isotopes over the East China Sea. The stable isotope ratios and major ion components of tritium concentrations in monthly precipitation on Okinawa Island suggest that tritium concentrations are strongly influenced by the surrounding ocean throughout the year due to the dynamics of air masses. This study makes a significant contribution to the understanding of the behavior of tritium concentrations in monthly precipitation under the special environment of subtropical island regions. In order to investigate the source of high tritium concentration in monthly precipitation in the future, it is necessary to understand the supply of tritium from the stratosphere to the troposphere due to vertical convection of the atmosphere.