The role of the Indonesian Throughflow in equatorial Pacific thermocline ventilation

The role of the Indonesian Throughflow (ITF) in the thermocline circulation of the low-latitude Pacific Ocean is explored using a high-resolution prim itive equation ocean circulation model. Seasonally forced runs for a domain with an open Indonesian passage are compared with seasonally forced runs f or a closed Pacific domain. Three cases are considered: one with no through flow, one with 10 Sv of imposed ITF transport, and one with 20 Sv of ITF tr ansport. Two idealized tracers, one that tags northern component subtropica l water and another that tags southern component subtropical water, are use d to diagnose the mixing ratio of northern and southern component waters in the equatorial thermocline. It is found that the mixing ratio of north/sou th component waters in the equatorial thermocline is highly sensitive to wh ether the model accounts for an ITF. Without an ITF, the source of equatori al undercurrent water is primarily of North Pacific origin, with the ratio of northern to southern component water being approximately 2.75 to 1. The ratio of northern to southern component water in the Equatorial Undercurren t with 10 Sv of ITF is approximately 1.4 to 1, and the ratio with 20 Sv of imposed ITF is 1 to 1.25. Estimates from data suggest a mean mixing ratio o f northern to southern component water of less than 1 to 1. Assuming that t he mixing ratio changes approximately linearly as the ITF transport varies between 10 and 20 Sv, an approximate balance between northern and southern component water is reached when the ITF transport is approximately 16 Sv. I t is also shown that for the isopycnal surfaces within the core of the equa torial undercurrent, a 2 degrees C temperature front exists across the equa tor in the western equatorial Pacific, beneath the warm pool. The implicati ons of the model results and the temperature data for the heat budget of th e equatorial Pacific are considered.