Zinc (Zn) plays a crucial role in biological processes. In the global ocean, Zn and silicon (Si) exhibit a relatively constant ratio, suggesting a strong coupling between them. However, the processes governing their distributions are fundamentally different: Zn is primarily taken up in organic particles, whereas Si is mainly assimilated to diatom frustules. Because of their different remineralization process, the mechanisms behind this coupling have long been debated.

Recent advances in observational techniques and the accumulation of oceanographic data have enabled more detailed discussions on this coupling. Vance et al. (2017) proposed that the similarity in Zn and Si distributions originates from the uptake in the Southern Ocean and subsequent water transportation through water mass formation are key processes to the Zn-Si coupling. However, observational studies report that this coupling is disrupted in the subarctic North Pacific, where Zn-Si decoupling is evident in intermediate waters. The Zn-Si relationship deviates from a linear trend. While several hypotheses have been proposed to explain this decoupling, none have been quantitatively validated, and the specific mechanisms driving it remain quantitively unclear.
Our previous study suggested that Zn-Si decoupling in the North Pacific could be attributed either to Zn inputs from the continental shelf or to differences in the regeneration processes of Zn and Si. The conclusions varied depending on the ocean circulation fields used in model experiments. A key limitation of our previous study was the inability to accurately reproduce regenerated Zn concentrations in the subarctic North Pacific. 
In this study, we refine the circulation fields by applying an inverse approach that incorporates observed distributions of phosphate (P) and Si, as well as temperature, salinity, ∆14C, and preformed P. By utilizing improved circulation fields, we provide a more robust quantitative assessment of the mechanisms contributing to Zn-Si decoupling in the
North Pacific. 

The results revealed that the global Zn–Si coupling is not maintained only by the preformed relationship in the Southern Ocean. Instead, it is established by a delicate balance between two opposing internal processes: regeneration from organic particles, which tends to accumulate Zn at shallower depths (decoupling Zn from Si), and reversible scavenging, which transports Zn from intermediate waters to the deep ocean (coupling Zn with Si). Regarding the subarctic North Pacific, the model demonstrated that internal cycling alone (regeneration and scavenging) cannot explain the observed decoupling. We quantitatively concluded that the supply of high-concentration Zn originating from the continental shelf of the western Bering Sea is the decisive factor driving the Zn–Si decoupling. 

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