Do tropical cells ventilate the Indo‐Pacific Equatorial Thermocline?

Source waters of the Indo‐Pacific equatorial thermocline are studied with a high‐resolution ocean model. In the annual mean fields, tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively. Tropical cells are common in ocean models, but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters. The tropical cells are much weaker when the overturning is considered in density coordinates. When high‐frequency mass fluxes are included tropical cells are compensated by an eddy‐induced overturning. Seasonal variations and tropical instability waves are responsible for the compensation. It follows that only subtropical cells transfer surface water to the equatorial thermocline. Strong tropical cells are shown to be an artefact.