The equatorial thermocline

In the temporary absence of surface winds, density gradients in the ocean can give rise to an eastward equatorial current which has a width, depth and maximum speed comparable to that of the equatorial undercurrent. This is offered as an explanation for the deeper of the two eastward currents (the one in the thermocline) which Hisard, Merle and Voituriez (1970) observed at the equator in the western Pacific. It also explains the eastward surface current observed at the equator when the trade winds are weak or absent. One striking feature of the meridional circulation is the occurrence of downwelling. It is suggested that this accounts for the downward spreading of the equatorial thermocline and for the deep penetration of water of high oxygen and low phosphate concentration at the equator.