Ventilation of the Subtropical North Pacific

Abstract

The ventilation of the subtropical North Pacific is studied using a simple analytical model. The model is forced by winter mixed layer density and depth calculated from the Levitus climatology and wind stress curl from the Hellerman and Rosenstein wind stress data. The wind-driven gyre in the North Pacific is shallow, no more than 1.4 km. The gross feature of the subduction rate is very similar to the results by Huang and Qiu based on data analysis of the Levitus climatology, with a total ventilation rate of 31.3 Sv (Sv ≡ 10⁶ m³ s⁻¹), including 20.8 Sv due to the vertical pumping and 10.5 Sv due to lateral induction. The age of water within the ventilated thermocline is relatively young, it is no more than 10 years old, except near the southeast corner of the basin. The young age indicates a fast communication between the atmosphere and the upper ocean on a timescale of less than 10 years. The vertical mass partition is slightly different from the results based on analysing climatology by Huang and Qiu. Most importantly, the total mass flux in the unventilated thermocline is about 28.3 Sv, smaller than the 31.3 Sv obtained by analysing the climatology.