Cadmium in the southwest Pacific Ocean two factors significantly affecting the Cd---PO4 relationship in the ocean

Vertical profiles of dissolved Cd were determined in the southwest Pacific Ocean, which includes the Tasman Sea, the Solomon Sea, and the Coral Sea. Cd shows a nutrient type distribution, but weakly correlates with phosphate compared to the North Pacific Ocean when all data are plotted. The Cd/PO4 ratio in surface layer is < 0.1 nM/μM and the ratio in the intermediate and deep water shows an increase approaching the Pacific value of ˜ 0.3 nM/μM. The Cd/PO4 ratio in the regeneration process has been estimated using an AOU (apparent oxygen utilization) respiration model. This ratio is affected by that in surface layer, so deep water receives a regeneration flux with a low Cd/PO4 ratio. The preformed Cd and phosphate as estimated by the AOU relation are low in the surface layer and high in the deep layers. The intermediate water is a mixture of surface water and Antarctic Intermediate Water (AAIW). The characteristic Cd---PO4 relationship in this area would be a consequence of mixing with two water masses which have different original Cd/PO4 ratios. The factors affecting the Cd---PO4 relationship in the world ocean are physical mixing and biological cycling, based on the results of the southern Pacific Ocean.