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

Preformed Cd and PO4 were investigated in the northwestern Pacific (Station CMO5) and the Okhotsk Sea (Station CMO6), and the relationship between the two elements was examined. At CMO5, from the apparent oxygen utilization (AOU)-Cd and PO4 plot, the different molecular ratios of consumed O-2 to regenerated Cd and PO4 were calculated to be 254,000 (Cd) and 96 (PO4) for the shallow layer (30-99 m) and 613,000 (Cd) and 170 (PO4) for the deep layer (below the oxygen minimum layer), which suggested the preferential remineralization of Cd and Po-4 in the shallow layer. At CMO6, regeneration ratios of O-2/Cd, PO4 were obtained only in the shallow layer (29-124 m) as 227,000 (Cd) and 75 (PO4). The calculated preformed Cd and PO4 concentrations in the shallow layer were 0.59 nM of Cd and 1.6 muM of PO4 at CMO5 and 0.35 nM of Cd and 0.95 muM of PO4 at CMO6. 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 CMO5, preformed concentrations were 0.64 nM of Cd and 1.4 muM of PO4. Preformed PO4 generally agreed with previously reported values in the Pacific, which suggested that the concentrations of the initial PO4 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 CaCO3 dissolution during the northward movement was considered. A plot of Cd and PO4 showed a linear relationship with slopes of 0.34 and 0.40 (nM/muM) at CMO5 and CMO6, respectively, which generally agreed with the reported values in the North Pacific. (C) 2002 Elsevier Science B.V. All rights reserved.