Sectional distribution patterns of Cd, Ni, Zn, and Cu in the North
Pacific Ocean: Systematic importance of scavenging
Abstract
The North Pacific Ocean is the largest basin and is located at the end
point of the thermohaline circulation of deep water. Few concurrent data
of Cd, Ni, Zn, and Cu in seawater have been reported in this area so
far. Herein, we report the basin-scale full-depth sectional
distributions of the total dissolvable, dissolved, and labile
particulate Cd, Ni, Zn, and Cu along the 160°W, 165°E, and 47°N
GEOTRACES transects. Our data reveal that the relations of the four
dissolved metals (dMs) with Si(OH) and PO considerably differ from those
in other oceans. The plot of the preformed Cd vs. the preformed PO
exhibits strong linearity and passes an origin.The dCd/PO ratio is
0.34±0.02 mmol/mol at a depth lower than 800 m, which is in the range of
the phytoplankton Cd/PO ratio, thus indicating the dominant effect of
the biogeochemical cycling on the dCd distribution. The dMs/POratios of
the other examined metals are partially or completely out of the
phytoplankton ratios and generally increase with depth in waters deeper
than 800 m. Specifically, the increase is the strongest for Cu and
moderate for Ni and Zn. The dMs/PO ratios below 800 m decrease with the
apparent oxygen utilization increasing from 150 to 300 mmol/kg by 4%
for Cd, 21% for Zn and Ni, and 69% for Cu. We thus demonstrate that
scavenging is an important factor that significantly affects the
distributions of Zn, Ni, and Cu, whereas the effect increases in the
order Cd < Ni, Zn < Cu.