Thermocline ventilation and pathways of tropical-subtropical water mass exchange

The mechanism of thermocline ventilation is investigated using a global, high-resolution ocean GCM, with realistic topography and surface wind forcing. Because 2-dimensional representations of circulation can be misleading, the subsurface flow is examined by visualizing the trajectories of particles which subduct in the mid-latitudes and travel within the ventilated thermocline. Three model runs are performed, each with identical surface forcing but with different initial particle distributions. Results from these runs show that the pathways of water mass exchange between the tropics and the subtropics are functions of the surface wind forcing, background density structure, and basin geometry. In the Pacific, ventilated waters from the northern and southern mid-latitudes reach the tropical thermocline through both the western boundary and the interior of the basin. In the Atlantic Ocean, the equatorial thermocline is ventilated primarily through water mass exchange with the southern hemisphere alone. In the Indian Ocean, the pathways of water mass exchange have patterns similar to those in the Atlantic and Pacific basins, though the lack of a mid-latitude gyre in the northern basin restricts the deep subduction and ventilation to the southern hemisphere.