Distribution of radioisotopes in sediment cores from nearshore off Xinghua Bay mouth, Fujian, China

Two marine sediment cores were collected from nearshore off Xinghua Bay mouth in Fujian, China and the K-40, Cs-137, Pb-210, Ra-226, Ra-228, Th-228 and U-238 in the cores were measured using gamma-spectroscopy. For the core ZK6, the activities of K-40 were vertically homogeneous within measured error in the whole core and Ra-226, Ra-228 and Th-228 showed large vertical variations with the same tendency. The sedimentation rates were 0.400 cm.y(-1) above 50 cm and 0.737 cm.y(-1) below depth of 50 cm. The change of sedimentation rates indicates the heterotaxy, which was justified by the absence of Cs-137 in the zone of 25-50 cm. For core ZK6, the sedimentation rate was 0.179 cm.y(-1). Vertical distributions of K-40, Ra-226, Ra-226, Th-228 and U-238 in the core ZK18 are similar to each other although there were significant large variations with depth. The large variations of radioisotopes with depth in the cores mean that the sediment cores have been disturbed largely due to marine environment change. The mean activities of radioisotopes in the core ZK6 are higher than ZK 18 that may be ascribed to different hydrodynamic environments