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Subarctic Pacific Intermediate Water: An Oceanic Highway for the Transport of Trace Metals in the North Pacific

GEOTRACES is an international collaboration project aiming to unravel the distributions of trace elements and their isotopes in the global ocean. As part of the GEOTRACES‐Japan project, we carried out two surveys in the subarctic Pacific in 2012 and 2017. Here, we synthesize the outcomes of research completed so far associated with these surveys. Together our findings revealed that the Subarctic Pacific Intermediate Water is an efficient carrier of trace metals. Trace metals such as iron and manganese originating in coastal regions are transported far into the open ocean due to combinations of favorable conditions. First, the young upper Subarctic Pacific Intermediate Water receives fresh inputs of trace metals, which are stabilized by organic ligands, from terrestrial sources. Meanwhile, the lower Subarctic Pacific Intermediate Water has a relatively low dissolved oxygen concentration, which slows down scavenging processes and allows trace metals to persist in seawater. Decaying sinking organic matter also releases additional trace metals into the intermediate water. The Subarctic Pacific Intermediate Water has unusually high concentrations of dissolved zinc relative to silicate, even though zinc and silicate generally have strongly coupled distribution patterns in the global ocean. We hope that the datasets and insights generated by our surveys and associated studies can contribute to greater understanding of the subarctic Pacific and provide useful information for future studies.