North Pacific Intermediate Water: Progress in SAGE (SubArctic Gyre Experiment) and Related Projects |
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| Authors: | Ichiro Yasuda |
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| Institution: | (1) Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Hongo Bunkyo-ku, Tokyo 113-0033, Japan |
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| Abstract: | We survey the recent progress in studies of North Pacific Intermediate Water (NPIW) in SAGE (SubArctic Gyre Experiment), including
important results obtained from related projects. Intensive observations have provided the transport distributions relating
to NPIW and revealed the existence of the cross-wind-driven gyre Oyashio water transport that flows directly from the subarctic
to subtropical gyres through the western boundary current as well as the diffusive contribution across the subarctic front.
The anthropogenic CO2 transport into NPIW has been estimated. The northern part of NPIW in the Transition Domain east of Japan is transported to
the Gulf of Alaska, feeding the mesothermal (intermediate temperature maximum) structure in the North Pacific subarctic region
where deep convection is restricted by the strong halocline maintained by the warm and salty water transport originating from
NPIW. This heat and salt transport is mostly balanced by the cooling and freshening in the formation of dense shelf water
accompanied by sea-ice formation and convection in the Okhotsk Sea. Intensive observational and modeling studies have substantially
altered our view of the intermediate-depth circulation in the North Pacific. NPIW circulations are related to diapycnal-meridional
overturning, generated around the Okhotsk Sea due to tide-induced diapycnal mixing and dense shelf water formation accompanied
by sea-ice formation in the Okhotsk Sea. This overturning circulation may possibly explain the direct cross-gyre transport
through the Oyashio along the western boundary from the subarctic to subtropical gyres.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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| Keywords: | North Pacific Intermediate Water Kuroshio Oyashio Okhotsk Sea water mass anthropogenic CO2 |
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