Vertical distributions of 226Ra, 228Ra, and 137Cs activities in the southwestern part of the Sea of Okhotsk

We collected 14 water column seawater samples in the southwestern part of the Sea of Okhotsk and employed low-background γ-spectrometry with convenient minimal radiochemical processing to determine the activities of 226Ra (half-life t1/2 = 1600 y), 228Ra (5.75y), and 137Cs (30.2 y) of the samples. All of these nuclides exhibited unique vertical profiles; 226Ra, 228Ra, and 137Cs activities exhibit small variations from 50–500 m depth (226Ra, ~ 2 mBq l−1; 228Ra, ~0.4 mBq l−1; 137Cs, ~ 1 mBq l−1); These profiles can be explained by convective mixing of surface water to this layer.