Oceanographic variability off Ecuador associated with an El Niño event in 1982–1983

Resumen

The development of the 1982–1983 El Niño event is described by reference to the oceanographic conditions prevailing off Ecuador during the period 1982–1984. The first signs of the anomaly's onset off the Ecuadorian coast were observed in August 1982: the 16°C isotherm was found some 50 m deeper than normal along 82°30′W; this observation preceded by approximately 2 months the rapid rise in sea level, the appearance of warm sea surface temperature (SST) anomalies, and heavy rainfalls. By February 1983, the whole area off Ecuador was covered by very warm (29°–30°C) and low salinity (less than 33.0 parts per thousand) surface water. Two mechanisms seemed to be involved in the formation of the low‐salinity water: advection of northern water and dilution by local rainfall. Although the ocean surface was 4°C warmer than normal, the most notable changes took place throughout the water column: a strong depression of the thermocline and all the isotherms down to 15°C, the largest anomalies being observed over the 100‐m water column, up to 9°C at 50‐m depth. During the subsequent months SSTs continued to increase; thus the highest SST anomalies (6.3°C) were observed in May and June. Recovery from the 1982–1983 anomaly started in July 1983 with a general uprising of the isotherms and a fall in sea level. By October, the warm SST anomalies had dropped to 1.5°C. In November 1983, the presence of the equatorial front also attested to the return to normal of the oceanographic conditions in the region.