A SIMULATION OF THE ABYSSAL CIRCULATION IN THE NORTH PACIFIC-OCEAN .2. THEORETICAL RATIONALE

A theoretical rationale is given for the simulated abyssal circulation in the North Pacific detailed in Part I. A simple theory clarifies th e importance of the vertical change in area of the horizontal cross se ction of the basin owing to the existence of bottom topography, or bas in shape. With general upward vertical transport in the basin, a water column horizontally diverges and vertically shrinks as it rises in sp ite of the general upwelling, resulting in the tendency to produce an anticyclonic circulation. This hypsometric effect is detailed by Rhine s and MacCready. In the present case, this effect is present in the lo wer deep layer (3250-4250 m) and in the bottom layer (below 4250 m) of the North Pacific. In the lower deep layer, a single anticyclonic cir culation owing to this effect appears explicitly. In the bottom layer, however, this effect almost balances the cyclogenesis owing to the bo ttom water influx, resulting in essentially eastward interior flow. On the other hand, an anticyclonic gyre in the upper deep layer (1750-32 50 m) is maintained by the vertical shrinking of the water column owin g to the outflux from the North to the South Pacific, resulting in a r eversed pattern of the Stommel-Arons circulation.