Interannual Variability of Mixed Layer Dynamics in the Ecuadorian Ocean

Abstract

Time series spanning 22 years of monthly conductivity-temperature-depth profiles are used to examine upper water column temperature interannual variability near the Ecuador coastline. The sampling program began in 1992 (and continues) by Ecuador's National Institute of Oceanography of the Navy and National Fisheries Institute. The five coastal stations are located 8 NM away from the coast and extend from 2°S to 1°N. The anomaly data show marked interannual variations with distinct characteristics associated with El Niño Southern Oscillation (ENSO) indices. Heat content and the 20°C isotherm depth are both largest during El Niño periods and weakest during La Niña periods. The first mode empirical orthogonal function (EOF) decomposition of the anomaly coastal station data represents bulk variations of the thermocline depth and has temporal variability coupled to Niño 3.4 and 1+2 indices. Coastal observations are compared with observations obtained from the offshore TAO/Triton buoys located along 95°W from 2°S to 2°N. The EOF decomposition of TAO buoy time series shows similar spatial EOF structure. The first EOF amplitude time series from coastal and TAO station decomposition is correlated, showing that the dominant variability of the upper water column near the coast is coupled to variations along the equator and seaward of the Galápagos. Coupling between ENSO indices and ERA-1 zonal wind stress from the central Pacific (Niño 4) with observed coastal temperature structure shows that effects of El Niño forcing are strongly influencing the Ecuadorian Sea eastward of the Galápagos Islands.