ENSO 1986-87 at Mexican subtropical Pacific offshore waters

GUADALUPE DE LA LANZA ESPINO, IGNACIO GALINDO E.

Abstract

The thermo-oxy-haline structure down to 100 m depth was determined in September 1987 through eight selected stations obtained from a transect of 340 km long across offshore waters near Manzanillo, between 104 W and 108 W at 19 N The waters in the first 20 m were relatively warm, from 26.4 C to 33.1 C. The average at 5 m depth was 30 C. That means a positive surface anomaly of 1.5 C. Salinity was between 0.1-0.4 o/oo higher than normal at the surface and it showed to be increased in the whole water column. Oxygen was considered normal at the surface. From 20 m to 100 m depth it was found a subsurface warming. The largest temperature deviations from Eastropac 1967 is at 75 m depth (> 2σ). The 15 C thermocline was found depressed at depths as down to 100 m. At the same depths, and about 150 km from the coast, salinity attained its largest values, between 35.1 o/oo to 35.2 o/oo. Near the coast the oxygen minimum concentration was 0.7 ml/l whereas 200 km seaward it was 0.4 ml/l. The Oxygen Minimun Layer (1.07 ml/l) was found near the coast depressed to 100 m depth. These results indicate advection of subsurface warmer waters northwards, perhaps due to an strengthening or northward displacement of the Equatorial Countercurrent. The onset of ENSO 1986-87 episode was between October and November 1986 at Tumaco (1.8 N) and Acapuico (16 8 N) respectively. While at Ensenada (31.9 N) the largest anomalies of SST and sea level did not appear until December 1986 In spite that surface warming was observed in the Galapagos Islands in November 1986, however the onset of ENSO 1986.1987 at Chicama (7.9 S) on the South American coast occurred five months later, in April 1987. Positive anomalies of SST and sea level remained in December 1987 along the west coast of Central America and Mexico However there is a decaying trend toward normal.

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