Basic research on pathways of Pacific deep water with high-performance ocean circulation model.

为了阐明北太平洋深层环流的三维结构，利用一个具有真实海底地形的全球海洋环流模式进行了一系列的数值试验。所获得的结果总结如下：1。通过萨摩亚航道向北输送的深水/底层水取决于北太平洋深层垂直涡旋扩散系数的垂直分布，而其路径则强烈地受海底地形的控制。向北流动的水最终在夏威夷东北部盆地或热带盆地上升。因此，我们可以在东北太平洋盆地的深层找到最古老的水。在盆地中涌出的水，被纬向西流向西输送，并通过埃克曼吸力浮出海面。在热带盆地上升水的共同作用下，具有深层来源的地表水以印尼通过流的形式流出。年龄示踪实验和拉格朗日粒子实验很好地定义了这些途径。如果给出垂直涡旋扩散系数的垂直廓线，随着上层的急剧减小，大部分向西移动的水域在上层(温跃层下层)，沿着由上层深度(2000-3000m)所界定的西部边界返回太平洋南部洋面(Tsujino，1998)。根据观测研究，基于地转分析，这种回流是通过一些示踪观测在热带太平洋东部实现的，而不是像模型实验所建议的那样通过西部边界。我们检查了WHP切片上最近的示踪观察，即Delta14C、Delta3He和其他营养物质。事实证明，所有的示踪模式都表明，没有向南穿过太平洋赤道的流动。因此，在满足示踪观测和模式结果的前提下，“太平洋经向平面上深层不存在回流”是必要的。

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 follows1. 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.