The westward extension of the low-oxyty distribution in the Pacific Ocean off the west coast of South America

Abstract

The low-oxyty1 distribution off the west coast of South America is compared with the geostrophic circulation pattern on the isanosteric surfaces of 160 and 200 cl ton−1 using data taken aboard the R.V. Alaminos during February–March 1967. On the 160 cl ton−1 surface the low oxyty distribution extended westward in two tongues, one at 4°S and the other at 13°S, divided by high-oxyty water carried eastward by what appears to have been the South Equatorial Countercurrent. These tongues did not coincide with westward flow as Tsuchiya (1968) suggests, but rather lay principally in two cyclonic shear zones. The low-oxyty zone at 4°S lay between the south branch of the Equatorial Undercurrent, as reported by Cochrane and Zuta (unpublished manuscript, 1969), and its return flow to the west along 5°S. The low-oxyty zone at 13°S lay between the South Equatorial Countercurrent and the Chile-South Equatorial Current. On the 200-cl ton−1 surface the low-oxyty zone at 4°S was not observable, but the low-oxyty band between the South Equatorial Countercurrent and the Chile-South Equatorial Current was intact, although displaced northward to 10°S in association with the boundary between these latter two currents.