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Abstract

Zinc (Zn) in the ocean is a trace metal and the distribution is controlled by the biological processes, and therefore it is considered a biogeochemically important element. The distribution of dissolved Zn in the global ocean is similar to that of silica (Si). Previous model-based experiments proposed the Southern Ocean hypothesis: the similarity of Zn and Si distribution spreads from the Southern Ocean surface to the global ocean. The hypothesis is based on the diatom Zn uptake characteristics and the water mass formation process in the Southern Ocean. However, observational data from the North Pacific showed that there is decoupling of Zn and Si: the correlation between Zn and Si breaks down in the North Pacific. The objective of this study is to understand the Zn cycle processes in the North Pacific with an ocean general circulation model, focusing on Zn-Si decoupling. We conducted the model experiment with various Zn uptake speeds in the surface ocean, but it was not easy to reproduce Zn concentrations in the North Pacific. By considering additional Zn sources from the continental shelves of the Sea of Okhotsk and the Bering Sea, we found that high Zn concentration and the Zn–Si decoupling in the North Pacific were reproduced, consistent with observational data. Our result suggests the Zn supply from the coastal regions in the North Pacific.