Overturning circulation that ventilates the intermediate layer of the Sea of Okhotsk and the North Pacific
Dense Shelf Water (DSW) formation in the northwestern continental shelf in 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...
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| Other Authors: | , , , |
| Format: | Other/Unknown Material |
| Language: | English |
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Hokkaido University
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| Online Access: | http://hdl.handle.net/2115/59451 https://doi.org/10.14943/doctoral.k11495 |
| Summary: | Dense Shelf Water (DSW) formation in the northwestern continental shelf in 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 been identified only vaguely. Using a high resolution North Pacific Ocean model with a curvilinear grid as fine as 3km × 3km 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 timescales 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 surface and intermediate layer is sensitive to wind stress. In 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 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 allow intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is extremely strong. We also examined the sensitivity to fresh water flux and found that salinity variations in the eastern Bering Sea propagates to the Sea of Okhotsk, and affects SSS in the Sea of Okhotsk and then overturning circulation. |
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