The distribution of uranium, radium and thorium isotopes in two anoxic Fjords : Framvaren Fjord (Norway) and Saanich inlet (British Columbia)

The behaviour of the naturally-occurring radionuclides uranium-238, uranium-234, radium-226, radium-228, and thorium-228 in two anoxic marine environments, the permanently anoxic Framvaren Fjord in southern Norway and the intermittently anoxic Saanich Inlet in British Columbia, were examined. In Framvaren, dissolved uranium-238 behaved conservatively throughout the water column, while dissolved radium-226 showed a sharp maximum just below the oxygen/hydrogen sulphide interface. In Saanich Inlet, uranium-238 showed a strongly non-conservative distribution. Reduction of particulate manganese appeared to regulate the behaviour of radium-226 and thorium-228 in the suboxic waters above the oxygen /hydrogen sulphide interface. Removal residence times for dissolved thorium-228 in the oxic surface waters of both systems are discussed.