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Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific : Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre

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Title: Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific : Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre
Authors: Nakanowatari, Takuya Browse this author →KAKEN DB
Mitsudera, Humio Browse this author
Motoi, Tatsuo Browse this author
Ishikawa, Ichiro Browse this author
Ohshima, Kay I Browse this author
Wakatsuchi, Masaaki Browse this author
Issue Date: 30-Apr-2015
Publisher: American Meteorological Society
Journal Title: Journal of Physical Oceanography
Volume: 45
Issue: 4
Start Page: 988
End Page: 1008
Publisher DOI: 10.1175/JPO-D-13-0274.1
Abstract: Using oceanographic observations and an eddy-resolving ice–ocean coupled model simulation from 1955 to 2004, the effects of the wind-driven ocean circulation change that occurred in the late 1970s during multidecadal-scale freshening of the North Pacific Intermediate Water (NPIW) at salinity minimum density (;26.8 su) were investigated. An analysis of the observations revealed that salinity decreased significantly at the density range of 26.6–26.8 su in the western subtropical gyre, including the mixed water region (MWR). The temporal variability of the salinity is dominated by the marked change in the late 1970s. With results similar to the observations, the model, selectively forced by the interannual variability of the wind-driven ocean circulation, simulated significant freshening of the intermediate layer over the subtropical gyre. The significant freshening is related to the increase in southward transport of the Oyashio associated with the intensification of the Aleutian low. Accompanying these changes, the intrusion of fresh and low potential vorticity water, originating in the Okhotsk Sea, to the MWRincreased, and the freshening signal propagated farther southward in the western subtropical gyre during the subsequent 6 yr, crossing the Kuroshio Extension. These results indicate that the multidecadal-scale freshening of the NPIW is partly caused by intensification of the wind-driven cross-gyre transport of the subarctic water to the subtropical gyre.
Rights: © Copyright 2015 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at ( or from the AMS at 617-227-2425 or
Type: article
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 中野渡 拓也

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