THE CONTRIBUTION OF THE GLOBAL THERMOHALINE CIRCULATION TO THE PACIFIC TO INDIAN-OCEAN THROUGHFLOW VIA INDONESIA

World ocean simulations are used to investigate the pathways feeding t he Indonesian throughflow as a function of depth, including the role o f the global thermohaline (''conveyor belt'') circulation. The simulat ions use a horizontal resolution of 1/2 degrees for each variable and the vertical resolution ranges from 1.5-layer reduced gravity to six l ayers with realistic bottom topography. They are forced by the Hellerm an and Rosenstein [1983] monthly wind stress climatology. Contrary to the classical theory of Stommel and Arons [1960], the Naval Research L aboratory model shows the Antarctic Circumpolar Current (ACC) region a s the main region of abyssal to upper ocean water upwelling which comp ensates for the deep water formation in the far North Atlantic, a resu lt corroborated by recent observational evidence [Toggweiler and Samue ls, 1993]. We examine the contribution of the global conveyor belt cir culation to the throughflow by systematically varying the model dynami cs (e.g., by disabling the far North Atlantic ports which parameterize deep water formation in that region). The model simulations show a gl obal conveyor belt circulation contribution of 5.7 Sv to the throughfl ow, a contribution provided mainly by wind-driven upwelling in the Ind o-Pacific ACC region. This is due to a cooperative interaction between the thermohaline and wind-driven circulations. The thermohaline circu lation makes the throughflow more surface trapped and less subject to topographic blocking in the Indonesian passageways, while the wind-dri ven circulation provides the Indonesian throughflow pathway for the th ermohaline flow upwelled in the ACC region. Mean layer transport field s, cross-layer mass transfer fields, and Lagrangian tracers are used t o identify pathways feeding the Pacific to Indian Ocean throughflow vi a Indonesia. Starting from the ACC, Sverdrup flow shows a circuitous r oute that is northward in the eastern South, Pacific, then westward in the South Equatorial Current (SEC). The SEC retroflects into the Nort h Equatorial Countercurrent (NECC) followed by cyclonic flow around th e Northern Tropical Gyre and into the North Equatorial Current (NEC), then into the Mindanao Current, the Sulawesi Sea, the Makassar Strait, and the Indian Ocean. The depth-integrated pathways from nonlinear si mulations show the retroflection from the SEC into the NECC as a secon dary route and retroflection into the Equatorial Undercurrent (EUC) as the primary route. The EUC connects with the NECC by westward and the n northward flow on the northside of the EUC. The pathways as a functi on of depth can be presented in three layers: a surface layer, the lay er containing the EUC, and layers below the EUC. In the top layer the EUC to NECC connection is via upwelling from the EUC in the central an d east-central equatorial Pacific. Some of this upwelled water is retu rned to the EUC layer via downwelling at midlatitudes where it feeds i nto the NEC or SEC. Very little Water in the South Pacific EUC layer p asses into the Indian Ocean without upwelling into the surface layer f irst. While the pathways in the top two layers are complex and strongl y coupled and enter the Indonesian Archipelago from the northern hemis phere, below the EUC layer a very direct Pacific to Indian Ocean route is found: SEC-->Sulawesi Sea-->Makassar Strait.