Tidally modified western boundary current drives interbasin exchange between the Sea of Okhotsk and the North Pacific

Abstract The interbasin exchange between the Sea of Okhotsk and the North Pacific governs the intermediate water ventilation and fertilization of the nutrient-rich subpolar Pacific, and thus has an enormous influence on the North Pacific. However, the mechanism of this exchange is puzzling; current...

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Bibliographic Details
Published in:Scientific Reports
Main Authors: Shu, Hung-Wei, Mitsudera, Humio, Yamazaki, Kaihe, Nakamura, Tomohiro, Kawasaki, Takao, Nakanowatari, Takuya, Nishikawa, Hatsumi, Sasaki, Hideharu
Other Authors: Grant-in-Aid for Scientific Research, Ministry of Education, Culture, Sports, Science and Technology, Japan, Special Grant Program for International Students, Graduate School of Environmental Science, Hokkaido University, Japan
Format: Article in Journal/Newspaper
Language:English
Published: Springer Science and Business Media LLC 2021
Subjects:
Multidisciplinary
Okhotsk
Pacific
Subarctic
Online Access:http://dx.doi.org/10.1038/s41598-021-91412-y
http://www.nature.com/articles/s41598-021-91412-y.pdf
http://www.nature.com/articles/s41598-021-91412-y
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Summary:Abstract The interbasin exchange between the Sea of Okhotsk and the North Pacific governs the intermediate water ventilation and fertilization of the nutrient-rich subpolar Pacific, and thus has an enormous influence on the North Pacific. However, the mechanism of this exchange is puzzling; current studies have not explained how the western boundary current (WBC) of the subarctic North Pacific intrudes only partially into the Sea of Okhotsk. High-resolution models often exhibit unrealistically small exchanges, as the WBC overshoots passing by deep straits and does not induce exchange flows. Therefore, partial intrusion cannot be solely explained by large-scale, wind-driven circulation. Here, we demonstrate that tidal forcing is the missing mechanism that drives the exchange by steering the WBC pathway. Upstream of the deep straits, tidally-generated topographically trapped waves over a bank lead to cross-slope upwelling. This upwelling enhances bottom pressure, thereby steering the WBC pathway toward the deep straits. The upwelling is identified as the source of joint-effect-of-baroclinicity-and-relief (JEBAR) in the potential vorticity equation, which is caused by tidal oscillation instead of tidally-enhanced vertical mixing. The WBC then hits the island chain and induces exchange flows. This tidal control of WBC pathways is applicable on subpolar and polar regions globally.

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