In physical oceanography, the active exchange of waters and/or water mass properties between basins. Evidence for this process is provided by the similarities in water masses in the three major oceans despite quite different water mass conversion processes in each. The three avenues for this in the world ocean are: the Bering Strait, which provides a conduit for North Pacific-North Atlantic exchange via the Arctic Ocean; passes in the Indonesian Archipelago, which connect the Indian and Pacific Oceans at low latitudes; and the Southern Ocean, in which the ACC flows through several broad passages between Antarctica and the other southern hemisphere continents. The conveyor belt paradigm was the first attempt to tie these together into a unified theory of interbasin circulation.

The most up-to-date scenario for these interbasin circulation processes starts with 14 Sv of upper and intermediate level water being converted to NADW in the North Atlantic and flowing southward across the equator to join the ACC. This loss from the Atlantic is compensated by 10 Sv of upper level entering via the Drake Passage and 4 Sv entering from the Indonesian throughflow through the Australasian Mediterranean and around Africa. The Indian Ocean receives 24 Sv of lower level cold water from the ACC, returning 14 Sv as cold water and transforming 10 Sv to upper level water. This latter 10 Sv flows south of Australia, across the South Pacific, and through the Drake Passage into the Benguela Current regime. This joins the afore mentioned Indonesian Throughflow, crosses the equator, and flow with the Gulf Stream into the North Atlantic to replace the lost NADW. The Pacific takes 20 Sv of cold water from the ACC and returns it as less cold water, with about half of it traversing the North Pacific.

This is a simplified two-layer version of a more complicated four-layer circulation scheme developed by Schmitz (1995) which includes intermediate and upper layer compensations flows as well as abyssal and deep interbasin thermohaline circulation layers. The greatest uncertainties remain in the Indian and Pacific Oceans, especially with the flows associated with vertical exchange, which in itself is perhaps the least well established feature of ocean circulation.