Equatorial subthermocline currents across the Pacific

Recent sections crossing the equator at nine longitudes from 146 degrees E to 86 degrees W show zonal currents below 400 m similar to those found in a 16-month mean section on 159 degrees W from the Pacific Equatorial Ocean Dynamics (PEQUOD) program in 1982-1983, Most of the new measurements were made with a lowered acoustic Doppler current profiler. Eastward current extrema (North and South Intermediate Countercurrents) are found in all sections about 2 degrees from the equator in the depth range 500-1500 m, with the possible exceptions of 146 degrees E, where topography complicates the picture south of the equator, and 150 degrees E, where the sections extend only from 1 degrees S to 2 degrees N. Poleward of the intermediate countercurrents, westward flow is found near 3 degrees from the equator in most of the sections. On the equator, from 250-500 m depth, a westward Equatorial Intermediate Current is found in many but not all of the sections. Similarly, it is present in the PEQUOD mean but not in all synoptic sections. Below the intermediate currents and countercurrents, an eastward current near 3000 m was found at and south of the equator in the PEQUOD mean and in the new sections from 150 degrees E to 110 degrees W. Near 4000 m there is westward flow south of the equator in the PEQUOD mean and near the equator in the new sections from 179 degrees E to 135 degrees W. Geostrophic currents calculated from an 8-year mean hydrographic section at 165 degrees E also resemble the PEQUOD mean. Although not conclusive, the evidence presented here indicates that these currents are basin-scale components of the general circulation, perhaps involving vigorous horizontal recirculation in a set of basin-wide elongated gyres within a few degrees of the equator.