2007 Fiscal Year Final Research Report Summary
Direct turbulence observation around Kuril Straits and studies on the impact of the tidal mixing on the North Pacific
| Project/Area Number |
17253004
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | The University of Tokyo |
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Principal Investigator |
YASUDA Ichiro The University of Tokyo, Ocean Research Institute, Professor (80270792)
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| Co-Investigator(Kenkyū-buntansha) |
HIBIYA Toshiyuki The University of Tokyo, Graduate School of Science, Professor (80192714)
KEIICHIRO Oshima Hokkaido University, Institute of I ow Temperature Science, Associate Professor (30185251)
YASUHIRO Kawasaki Fisheries Research Agency, Hokkaido National Fisheries Research Institute, Senior Researcher (20416027)
WATANABE Yutaka Hokkaido University, graduate School of Encvironmental, Associate Professor (90333640)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Ocean / tide / Pacific / turbulence / climate / phvsic / Okhotsk Sea / mixing |
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| Research Abstract |
North Pacific marine ecosystem including tuna and small pelagic fish as sardine and anchovy is known to be related with inter-decadal ocean-climate variability. However, multi-decadal time-scale ocean-climate variability and mechanism remain unclear and thus unpredictable. Present studies discovered the relationship between the 18.6-year period nodal tidal cycle caused by lunar orbital variation and the bi-decadal variability of water-masses in the northwestern subarctic Pacific and of the North Pacific climate indices as winter NPI (North Pacific Index), PDO (Pacific Decadal Oscillation Index) and MOI (east-Asian Monsoon Index). Direct turbulence observations by the Russian Vessel Khromov evidenced the strong tidal mixing around the Kuril Straits; the vertical diffusivity reached over 1000 cm2/s, which is roughly 10,000 times the value (0.1 cm^<2>/s) in ordinary open ocean intermediate depths. Changes in this strong tidal mixing associated with the 18.6-year period tidal cycle probabl
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y change the surface salinity in the Okhotsk Sea and then intermediate water formation (sinking) rate in the northwestern shelf region. This explains the observed bidecadal variations in the intermediate waters in the Okhotsk Sea and Oyashio. The isopycnal depth changes observed around the Kuril Straits and along the east coast of Hokkaido and Tohoku propagate as coastally trapped wave and may change the Kuroshio intensity and heat transport. This coastal change may reach the equator and may influence the ENSO. These changes in the ocean could lead to the changes in the Aleutian Low Pressure, through atmospheric teleconnection. The present study linked the astronomically predictable 18.6-year period tidal cycle and with small-scale ocean mixing phenomena, and explained the surface to intermediate depths water-mass bi-decadal variability in the North Pacific subarctic regions. This study also proposed the link with the oceanic circulation and North Pacific climate variability. These open the predictability of multi-decadal scale ocean-climate-ecosystem variability. Since the tidal mixing considerably changes temporally and spatially, we need further observation of turbulence in mixing hot spots to make clear the strong mixing mechanism and to quantify the mixing. Studies are going on about the vertical transport of nutrients and influence on long-term marine ecosystem variability and diapycnal water transport and influence on the ocean circulation and climate. Less
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