Circulation and ventilation flux of the Pacific Ocean

Abstract

The flux of water from the mixed layer into the thermocline/intermediate layers of the Pacific Ocean is quantified using chlorofluorocarbon (CFC) and hydrographic data. The total ventilation flux of at least 123 Sv for the South Pacific (SP) only slightly exceeds that of at least 111 Sv for the North Pacific (NP). Although the overall ventilation flux (to 27.3 σθ) is similar in the NP and SP, the partitioning amongst the water masses is markedly different. In the NP the partitioning is equal between the wind‐driven (≤26.5 σθ) and thermohaline (>26.5–27.3 σθ) layers. While in the SP the ventilation flux of the thermohaline layers exceeds by nearly 2:1 the wind‐driven layers. The wind‐driven subtropical gyre thermocline ventilation flux for the NP (41 Sv) exceeds the SP (25 Sv), and both agree well with literature estimates of Sverdrup transports. The ventilated volumes and ages are related to the wind stress curl and surface buoyancy fluxes. In the thermocline ventilation of Shallow Salinity Minimum Water (22 m yr−1 in the NP, 15 m yr−1 in the SP) and Subtropical Mode Water is more effective in the NP than in the SP. In contrast, in the thermohaline layers direct air‐sea exchange during convective formation of Subantarctic Mode and Antarctic Intermediate Water is more effective in ventilating the SP than processes in the NP. These same differences are also used to explain the larger volume of the shadow zone in the NP. In the subpolar regions the ventilation fluxes can be used to infer formation rates of 8 Sv for the NP Intermediate Water and 9 Sv for the Subantarctic Mode Water. Into the tropical Pacific there is a substantial flux of 35 Sv of extratropical water for the wind‐driven layers and 36 Sv for the thermohaline layers. The relatively young (5–20 years increasing with increasing density) CFC‐derived ages show that a climate anomaly introduced into the subtropical thermocline could be transported into the tropics relatively quickly.