ON THE INTERBASIN-SCALE THERMOHALINE CIRCULATION

The global-scale circulation has long been one of oceanography's most challenging and exciting research topics. A few features of the abyssa l (near bottom) and deep circulation of the Atlantic Ocean have been k nown for over 50 years, and in the past decade or so there has been a developing focus on the world oceans' thermohaline circulation. The te rm thermohaline circulation as used here applies not only to a direct response to atmospheric buoyancy fluxes but also in the general sense of water mass modification or conversion, where mechanisms may be asso ciated with internal mixing processes and even wind forcing (i.e., win d-induced upwelling or wind-driven mixing). The thermohaline circulati on components reviewed and summarized in the following are associated with water mass conversion processes that are involved with interbasin exchange, Updated summary maps of the volume transports (in sverdrups ; 1Sv = 10(6) m(3) s(-1)) for the interbasin-scale pathways of the aby ssal and deep thermohaline circulation and associated upper level comp ensating flows are developed for two to four vertical layers or potent ial density intervals, based primarily on a synthesis of published obs ervational results. The cell(s) involving the largest worldwide exchan ge transport-wise (53 Sv) are associated with an interaction between v arious deep and bottom water components via Circumpolar Deep Water (CD W). The first major conversion step in the replacement path for the re newal (14 Sv) of North Atlantic Deep Water (NADW) is taken to be prima rily to CDW. Bottom water in the Indian Ocean originates as lower CDW which recirculates while also moving equatorward in deep western bound ary currents with eventual conversion to both deep and intermediate la yer flows. Some of the intermediate water so formed in the Indian Ocea n moves through the Agulhas Current system (ACS) and may ''leak'' into the Benguela Current regime (BCR), although probably primarily flowin g through the ACS into the Subantarctic Frontal Zone (SFZ). It is modi fied throughout its transit in the SFZ south of the Indian Ocean, sout h of Australia, and across the South Pacific. Up to 10 Sv of the least dense brand of intermediate water flows through the northern sector o f Drake Passage, becomes involved in a Malvinas Current-Brazil Current -Subtropical Gyre interaction, and then joins the BCR after perhaps al so interacting with the ACS again. This compensating flow is warmed an d becomes more saline in the South Atlantic and is later further modif ied and upwelled in the equatorial Atlantic, crossing the equator and moving through the Gulf Stream system to replace NADW. There is also a n NADW replacement path of secondary importance westward around the ti p of Africa (similar to 4 out of 14 Sv) associated with an interbasin circulation pattern throughout the southern hemisphere oceans involvin g an O(10 Sv) Indonesian Throughflow.