THE ROLE OF INDONESIAN THROUGHFLOW IN A GLOBAL OCEAN GCM

The effect of the Indonesian Throughflow on the World Ocean circulatio n is examined by a series of experiments with a global ocean GCM. The principal objective is to gain an understanding of how ocean flows res pond to the throughflow, and how these changes result in changes in th e pattern of surface heat flux and sea surface temperature. Four model runs are conducted. The first run features an open Indonesian passage through which a nonzero net throughflow is permitted. The second run features a complete blockage of the Indonesian passage. The third run is designed to isolate the effects of purely buoyancy-driven throughfl ow: the Indonesian passage is open but the net volume transport is req uired to be zero. The fourth run is designed to isolate the effects of nonzero net throughflow on the Indian Ocean, independent of interocea n buoyancy differences: the Indonesian passage is open but the through flow water is cooled and salted toward profiles characteristic of the east Indian Ocean in the absence of throughflow. Comparison of the fir st and second runs shows that the throughflow generally warms the Indi an Ocean and cools the Pacific. However, large changes in the surface temperature and heat flux are restricted to certain well-defined regio ns: the Agulhas Current/outflow, the Leeuwin Current region off wester n Australia, the Tasman Sea, the equatorial Pacific, and two bands in the midlatitude South Pacific. In contrast, large subsurface temperatu re changes are widespread across both oceans. Heat budget analysis ind icates that the large surface responses are dependent on the subsurfac e temperature change being brought to the surface, either by strong wi nd-forced upwelling (as in the equatorial Pacific) or by vigorous mixi ng in convective mixed layers (as in the other regions). Over most of both oceans, such mechanisms are absent and surface heat-flux changes are small (a few W m-2). There, subsurface temperature perturbations a re largely insulated from the surface and may extend via direct advect ion or baroclinic wave propagation. The additional heat is released up on encounter with upwelling or a convective mixed layer, which may be far removed from the source of the perturbation. Atlantic and far Sout hern Ocean effects are mostly very small, possibly because of our use of restoring upper boundary conditions. The third and fourth runs brea k the throughflow into its baroclinic and barotropic components. The b aroclinic (buoyancy-driven) component affects surface heat flux strong ly in the Leeuwin Current region but relatively weakly in the Agulhas Current and Tasman Sea. The barotropic component has the converse effe ct. Interocean heat exchange is discussed; the full throughflow transp orts a net 0.63 petawatts out of the Pacific Ocean, which represents a bout one-third of the total heat input into the model's equatorial Pac ific.