An estimate of the upwelling rate in the tropical Pacific Ocean

Abstract

An inverse box model of the tropical Pacific Ocean from 321S - 10N is constructed from two zonal and six meridional hydrographic sections. This data is supplemented with LADCP data close to the equator where geostrophy fails. A consistent solution is found despite the presence of a number of mid-ocean crossing points and the data being spread over many years and seasons. The total upwelling across the ... = 23.5 isopycnal surface in a 60 latitude band centered on the equator is estimated to be 55 ± 27Sv. The zonal mean cross-isopycnal velocity for the same surface in the same latitude band is estimated to be 6.88 t 3.23 x 10 4 cms- 1. The addition of radiocarbon data places a strong constraint on the vertical transfers in the model and significantly reduces the error on the estimated vertical transport and velocity. When radiocarbon constraints are included, the upwelling across the ... = 23.5 isopycnal surface in the equatorial zone is estimated to be 52 ± 16Sv and the zonal mean cross-isopycnal velocity across the same surface is estimated as 7.15 t 1.90 x 10- 4 cms-1 . That a consistent solution can be found is encouraging but it remains unclear whether one-time data is representative of mean conditions in a region which is known to be highly variable.