| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2004: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
A series of numerical experiments are made by use of a global ocean general circulation model with realistic bottom topography, in order to clarify 3D structure of the North Pacific deep layer circulation. Results obtained are summarized as follows
1. Northward transport of deep/bottom waters through Samoan passage is dependent upon vertical profile of vertical eddy-diffusivity in the North Pacific deep layer, whereas their pathways are strongly controlled by bottom topography. Waters moving northward eventually upwell either in Hawaiian north-eastern basin or in tropical basins. Therefore, we can find the oldest water in the deep layers of the north-eastern Pacific basin. Waters upwelled in the basin, are transported westward by the zonal westward currents and emerged to the sea surface by the Ekman suction. Joined by the upwelled water in the tropical basin, surface waters with deep layer origin, flow out as Indonesian through flow. These pathways are well defined by age-tracer experiments and Lagrangean particle experiments.
2. If we give vertical profile of vertical eddy-diffusion coefficient with sharp decrease in the upper deep layer, most of the westward moving waters in the upper deep (lower thermocline level), returns to the Pacific southern ocean (Tsujino,1998) along the western boundary, defined by the upper deep depth(2000-3000m).
3. According to the observational studies, based on the geostrophic analysis, this return flow is realized in the eastern tropical Pacific with some tracer observation, contrary to via the western boundary as suggested by the model experiments.
4. We checked recent tracer observation along WHP sections, i.e., of delta14C, delta3He, and other nutrients. It turns out that all the tracer patterns indicate no southward flow across the Pacific equator.
5. Therefore, we conclude that, to satisfy both the tracer observation and the model results, "no return flow in the upper deep layer in the Pacific meridional plane" is required.
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