Thermocline ventilation and pathways of tropical–subtropical water mass exchange

The mechanism of thermocline ventilation is investigated using a global, high-resolution oceanGCM, with realistic topography and surface wind forcing. Because 2-dimensional representationsof circulation can be misleading, the subsurface flow is examined by visualizing the trajectoriesof 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 initialparticle distributions. Results from these runs show that the pathways of water mass exchangebetween the tropics and the subtropics are functions of the surface wind forcing, backgrounddensity structure, and basin geometry. In the Pacific, ventilated waters from the northern andsouthern mid-latitudes reach the tropical thermocline through both the western boundary andthe interior of the basin. In the Atlantic Ocean, the equatorial thermocline is ventilated primarilythrough water mass exchange with the southern hemisphere alone. In the Indian Ocean, thepathways of water mass exchange have patterns similar to those in the Atlantic and Pacificbasins, though the lack of a mid-latitude gyre in the northern basin restricts the deep subductionand ventilation to the southern hemisphere.