Oceanic concentrations of 228Radium

This paper evaluates the worldwide oceanic distribution of ²²⁸Ra. Nearshore waters, especially waters from restricted bays and sounds, are very high in unsupported ²²⁸Ra. The concentrations decrease away from land. The ²²⁸Ra content of surface waters bears a close correlation with the proximity to land. Samples from the Atlantic Ocean are higher than those from the Pacific Ocean. Apparently the source of ²²⁸Ra in surface waters is diffusion from ²³²Th-bearing sediments in contact with these waters. Deep water samples collected < 100m from the sea floor have significant ²²⁸Ra concentrations. Apparently ²²⁸Ra is diffusing from deep-sea sediments as it is from nearshore sediments. Deep Pacific samples are generally lower than deep Atlantic samples. This may mean that ²²⁸Ra released from Pacific sediments is mixed upward more rapidly, thereby decreasing the near-bottom concentrations. Intermediate water samples have less ²²⁸Ra than either surface or bottom samples from the same area. These concentrations are near the lower limit of detection. Because the vertical mixing rate of the ocean is much greater than the mean life of ²²⁸Ra, little ²²⁸Ra can penetrate into the intermediate ocean.