Seasonal variations of 228Ra/226Ra and 228Th/228Ra ratios in surface water from the eastern East China Sea

A total of 30 surface water samples were collected at 2 sites on the east side of the East China Sea (ECS) during 2008-2010, and 226 Ra, 228 Ra, and 228 Th activities were measured using low-background γ-spectrometry. The 228 Ra/ 226 Ra and 228 Th/ 228 Ra activity ratios of the samples exhibited notable seasonal variations ( 228 Ra/ 226 Ra = 0.2-3.3; 228 Th/ 228 Ra = < 0.1-0.4) accompanying salinity changes (31.0-34.6). These changes are hypothesized to cause the change by altering the mixing ratio of 228 Ra-rich and particle-rich continental shelf water within the ECS.