Tidally modified western boundary current drives interbasin exchange between the Sea of Okhotsk and the North Pacific
Shu, H.-W.; Mitsudera, H.; Yamazaki, K.; Nakamura, T.; Kawasaki, T.; Nakanowatari, T.; Nishikawa, H.; Sasaki, H. (2021). Tidally modified western boundary current drives interbasin exchange between the Sea of Okhotsk and the North Pacific. NPG Scientific Reports 11(1): 12037. https://dx.doi.org/10.1038/s41598-021-91412-y
In: Scientific Reports (Nature Publishing Group). Nature Publishing Group: London. ISSN 2045-2322; e-ISSN 2045-2322, more
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| Authors | | Top |
- Shu, H.-W.
- Mitsudera, H.
- Yamazaki, K.
- Nakamura, T.
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- Kawasaki, T.
- Nakanowatari, T.
- Nishikawa, H.
- Sasaki, H.
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| 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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