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Sectional distribution patterns of Cd, Ni, Zn, and Cu in the North Pacific Ocean: Systematic importance of scavenging
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  • Linjie Zheng,
  • Tomoharu Minami,
  • Shotaro Takano,
  • Tung-Yuan Ho,
  • Yoshiki Sohrin
Linjie Zheng
Kyoto University

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Tomoharu Minami
Kanazawa University
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Shotaro Takano
Kyoto University
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Tung-Yuan Ho
Academia Sinica
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Yoshiki Sohrin
Kyoto University
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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.