Abstract. Recently obtained World Ocean Circulation Experiment (WOCE) sections and pre-WOCE hydrography are used to study the water -mass structure and formation and transformation of North Pacific Intermediate Water (NPIW). Five neutral density surfaces are selected and mapped, encompassing NPIW from 400 to 900 m in the subtropical latitudes with a distance of-100 m between a pair of surfaces. NPIW is defined as a subtropical gyre salinity minimum which is well followed by a neutral density surface ON=26.9.
The thermohaline circulation of the ocean is often described in terms of downwelling sites in the Nordic and Labrador Seas with upwelling, produced by mixing due to breaking internal waves, throughout the rest of the ocean. Theoretical estimates 1,2 of the diapycnal (cross density surface) mixing coefficient required to do this give values near 10 -4 m 2 s -1 , an order of magnitude larger than most observed values 3,4 . The
Abstract.Observations indicate that vertical diffusivity in the deep ocean is considerably enhanced over rough bathymetry and is very small elsewhere. Here we investigate effects of locally enhanced vertical diffusivity over rough bottom topography on the world ocean circulation by use of a coarse resolution ocean general circulation model. Vertical diffusivity is enhanced in the model, taking into account effects of internal tide breaking. For comparison, two cases of an experiment are carried out, where vertical diffusivity increases with depth without horizontal inhomogeneity. Horizontal distribution of deep upwelling is qualitatively different, depending on whether or not vertical diffusivity is horizontally inhomogeneous. Upwelling of Circumpolar Deep Water in the Pacific and Antarctic Bottom Water in the Atlantic is confined where vertical diffusivity is enhanced in the case of horizontally inhomogeneous vertical diffusivity, whereas it is horizontally uniform in the other cases. This difference leads to different three-dimensional structure of the deep circulation.
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