Overturning circulation that ventilates the intermediate layer of the Sea of Okhotsk and the North Pacific: The role of salinity advection

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Matsuda, Junji, Mitsudera, Humio, Nakamura, Tomohiro, Sasajima, Yuichiro, Hasumi, Hiroyasu, Wakatsuchi, Masaaki
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union
• Subjects: overturning circulation; salinity advection; Sea of Okhotsk; wind stress; high‐resolution modeling; 450; Bering Sea; Okhotsk; Pacific; okhotsk sea; Subarctic
• Online Access: http://hdl.handle.net/2115/80686; https://doi.org/10.1002/2014JC009995

Dense Shelf Water (DSW) formation in the northwestern continental shelf of the Sea of Okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the North Pacific Ocean. The upper limb consisting of surface currents in the Okhotsk Sea and the subarctic gyre has not been clarified. Using a high‐resolution North Pacific Ocean model with a curvilinear grid as fine as 3 km × 3 km in the Sea of Okhotsk, we succeeded in representing the three‐dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb, as well as the lower limb consisting of DSW formation and ventilation. In particular, pathways and time scales from the Bering Sea to the intermediate layer via the ventilation in the Sea of Okhotsk were examined in detail using tracer experiments. Further, we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress. In the case of strong winds, the coastal current under polynyas where DSW forms is intensified, and consequently diapycnal transport from the surface layer to the intermediate layer increases. Strong winds also induce a positive sea surface salinity anomaly in the subarctic region, causing a significant decrease in the density stratification and increase in the DSW salinity (i.e., density). These processes act together to produce intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is strong.