Circulation, renewal, and modification of Antarctic mode and intermediate water

Nine hydrographic sections are combined in an inverse box model of the Sout hern Ocean south of similar to 12 degreesS. The inverse model has two novel features: the inclusion of independent diapycnal flux unknowns for each pr operty and the explicit inclusion of air-sea fluxes (heat, freshwater, and momentum) and the water mass transformation they drive. Transformation of 3 4 x 10(6) m(3) s(-1) of Antarctic Surface Water by air-sea buoyancy fluxes, and cooling and freshening where Subantarctic Mode Water outcrops, renews cold, fresh Antarctic Intermediate Water of the southeast Pacific and south west Atlantic. Relatively cold, fresh mode and intermediate water enter the subtropical gyres, are modified by air-sea fluxes and interior mixing, and return poleward as warmer, saltier mode and intermediate water. While the zonally integrated meridional transport in these layers is small, the gross exchange is approximately 80 x 10(6) m(3) s(-1). The air-sea transformation of Antarctic surface water to intermediate water is compensated in the Southern Ocean by an interior diapycnal flux of 32 x 10(6) m(3) s(-1) of intermediate water to upper deep water. The small prop erty differences between slightly warmer, saltier intermediate water and co ld, fresh Antarctic Surface Water results in a poleward transfer of heat an d salt across the Polar Front zone. Mode and intermediate water are crucial participants in the North Atlantic Deep Water overturning and Indonesian Throughflow circulation cells. The No rth Atlantic Deep Water overturning is closed by cold, fresh intermediate w ater that is modified to warm, salty varieties by air-sea fluxes and interi or mixing in the Atlantic and southwest Indian Oceans. The Indonesian Throu ghflow is part of a circum-Australia circulation. In the Indian Ocean, surf ace water is converted to denser thermocline and mode water by air-sea flux es and interior mixing, excess mode water flows eastward south of Australia , and air-sea fluxes convert mode water to thermocline water in the Pacific .