FY 1987

Hydrographic variability west of the Galápagos Islands during the 1982–83 El Niño

Hayes, S.P., L.J. Mangum, R.T. Barber, A. Huyer, and R.L. Smith

Prog. Oceanogr., 17(1–2), 137–162, doi: 10.1016/0079-6611(86)90026-1 (1986)

Nine hydrographic (temperature, salinity, and in some cases oxygen) and four zonal velocity sections near the equator along 95°W in 1980–1984 are presented and discussed. Perturbations associated with the 1982–83 El Niño form the focus for the discussion. This event was sampled by sections in November 1982 and in March, May, November and December 1983. The upper ocean response in November 1982 was a downward displacement of isotherms above 400 m on the equator. The Equatorial Undercurrent (EUC) was deep and strong for this season. The vertical displacement perturbations extended to at least 5°S and were more uniform with depth off the equator. In May 1983 the largest vertical displacements were observed. The EUC was replaced by a westward jet at about 75 m and the Equatorial 13°C Water thermostad had disappeared. Local estimates of the zonal pressure gradient suggest that between 110°W and 95°W this slope had reversed in May 1983 and was, at least in part, responsible for the observed westward jet. Local winds were westerly and forced the observed eastward surface current. By November 1983, surface conditions were fairly normal. However, the deeper stratification remained anomalous; the Equatorial 13°C Water thermostad was still missing. The vertical profile of vertical displacements from a mean suggested a complicated vertical structure near the equator. In April 1984 conditions had returned to near normal.