The Transit Time Distribution of the Subtropical-Tropical Water Exchange in the Pacific Ocean

The transit-time distribution (TTD) of the subtropical-tropical thermocline water exchange in the Pacific Ocean is simulated in an ocean general circulation model. The exchange time scales that are mainly due to advection are about 10 years, consistent with previous time scale estimates by neglecting the effect of mixing. However, only about 10% of the water in the equatorial thermocline has age less than the advective time scale, and the rest has age much longer due to mixing. In addition, the mean time scale, which considers the effects of both advection and mixing, for the subtropical surface waters to reach the equator is much longer (over 100 years) than the advective time scale. The long mean time scale and broad TTDs in the equtorial Pacific suggest that mixing is important for the thermocline water exchange.