Sectional Distribution Patterns of Cd, Ni, Zn, and Cu in the North Pacific Ocean: Relationships to Nutrients and Importance of Scavenging

Abstract

AbstractThe North Pacific Ocean is located at the end of the thermohaline circulation of deep water. This study reports on basin‐scale full‐depth sectional distributions of total dissolvable (td), dissolved (d), and labile particulate (lp) Cd, Ni, Zn, and Cu along three transects: the GEOTRACES transects GP18 (165°E) and GP02 (47°N), and along 160°W. We find that scavenging is an important factor that significantly affects the distributions of dZn, dNi, and dCu, of which the magnitude of influence increases in the order of Cd < Ni, Zn < Cu. The relationships between the four dissolved metals with Si(OH)4 and PO4 differed considerably from those in other oceans. The spot concentration ratio of dCd/PO4 was 0.34 ± 0.02 nmol/μmol (n = 296) in waters >800 m deep, which is in the range of the phytoplankton Cd/P ratio. This is indicative of the dominant effect of water circulation and biological processes on dCd distribution. The dissolved metals (dMs) to PO4 ratios of other examined metals were either partially or completely outside the range of typical biomass ratios. They generally increased with depth in waters >800 m deep; the magnitude of increase was the highest for Cu and moderate for Ni and Zn. Below 800 m, an increase in the apparent oxygen utilization from 150 to 300 μmol/kg was concurrent with a decrease in the dMs/PO4 ratios: 4 ± 3% for Cd, 21 ± 4% for Zn, 21 ± 3% for Ni, and 69 ± 7% for Cu.