Spatial variations of Ra-226, Ra-228, Cs-134, and Cs-137 concentrations in western and southern waters off the Korean Peninsula in July 2014

Abstract

We examined the spatial distributions of Ra-228, Ra-228, (CS)-C-134, and Cs-137 concentrations (activities) in seawater off the western and southern Korean Peninsula in July 2014. Raditun-228 (and Ra-226) concentrations in water samples varied widely from 5 to 14 mBq/L (2-4 mBq/L), showing a negative correlation with salinity, particularly at the surface off the western Korean Peninsula. This indicates that the seawaters in this area are fundamentally comprised of Ra-228-poor and high-saline Kuroshio Current water and Ra-228-rich and low-saline water (e.g., continental shelf water), with various mixing ratios. Although Fukushima Dai-ichi Nuclear Power Plant (FDNPP)-derived Cs-134 was below the detection limit (< 0.08 mBq/L) in waters off the western Korean Peninsula, low level Cs-134 (0.1-0.2 mBq/L) was detected in waters off the southern Korean Peninsula accompanied by higher Cs-137 concentrations (1.6-1.9 mBq/L) relative to that off the western Korean Peninsula. Combined with the lower radium concentrations, the detection of Cs-134 is explained by mixing of FDNPP-derived radiocesium-contaminated Kuroshio Current water.