Preformed Cd and PO4 and the relationship between the two elements in the northwestern Pacific and the Okhotsk Sea

Abstract

Abstract Preformed Cd and PO 4 were investigated in the northwestern Pacific (Station CM05) and the Okhotsk Sea (Station CM06), and the relationship between the two elements was examined. At CM05, from the apparent oxygen utilization (AOU)–Cd and PO 4 plot, the different molecular ratios of consumed O 2 to regenerated Cd and PO 4 were calculated to be 254,000 (Cd) and 96 (PO 4 ) for the shallow layer (30–99 m) and 613,000 (Cd) and 170 (PO 4 ) for the deep layer (below the oxygen minimum layer), which suggested the preferential remineralization of Cd and PO 4 in the shallow layer. At CM06, regeneration ratios of O 2 /Cd, PO 4 were obtained only in the shallow layer (29–124 m) as 227,000 (Cd) and 75 (PO 4 ). The calculated preformed Cd and PO 4 concentrations in the shallow layer were 0.59 nM of Cd and 1.6 μM of PO 4 at CM05 and 0.35 nM of Cd and 0.95 μM of PO 4 at CM06. These concentrations were much higher than those (close to 0) in the low-latitude area, which was attributable to the supply of these constituents from deep water by the strong winter convection. In the deep layer, at CM05, preformed concentrations were 0.64 nM of Cd and 1.4 μM of PO 4 . Preformed PO 4 generally agreed with previously reported values in the Pacific, which suggested that the concentrations of the initial PO 4 in the deep water were preserved as preformed through the movement to the northwestern Pacific. On the other hand, obtained preformed Cd in the northwestern Pacific deep water showed a somewhat higher value than that in the southwest Pacific. The possibility of the terrestrial input and remineralization of Cd by CaCO 3 dissolution during the northward movement was considered. A plot of Cd and PO 4 showed a linear relationship with slopes of 0.34 and 0.40 (nM/μM) at CM05 and CM06, respectively, which generally agreed with the reported values in the North Pacific.