Measurements of Equatorial Currents in the Gilbert Islands Area, July–August 1963

Abstract

IN a recent article, Montgomery¹ reviewed the observations of the equatorial undercurrent, a current which has been recorded at least seasonally in each ocean. This easterly flow is found near the equator, usually below a westerly surface current; the easterly velocity maximum is located within the thermocline. Measurements in the central Pacific Ocean have shown the undercurrent commonly to be separate from the easterly surface flow of the equatorial countercurrent to the north, to be symmetrical about the equator, to be relatively steady, and to have a maximum velocity of two to three knots. In the western Pacific Ocean, on the other hand, the data indicate that the undercurrent is by comparison less strong and less steady, is commonly not symmetrical about the equator, and is often joined to the equatorial countercurrent by a continuous layer of easterly flow. Montgomery chose the Gilbert Islands, which cross the equator at 174° E., as the natural dividing line between the central and western regions of the equatorial Pacific Ocean. This chain of islands apparently forms the only sizeable obstruction to the flow of the undercurrent between New Guinea and the Galapagos Islands, a distance of some 8,000 miles.