Evolution of an upwelling event off Punta Curaumilla, Valparaíso

Abstract

The beginning, maturity and relaxation phases of a coastal upwelling event (16 to 20 January 1986), off punta Curaumilla (33°06'S), were characterized. This characterization was based on the spatial and time distribution of temperature, salinity, dissolved oxygen, nutrients (nitrate, phosphate and silicate), wind and Ekman transport. Satellite images of sea surface temperature were used as complementary information. The results showed that the winds were fluctuating and mainly blowing from the south and southwest, so it was possible to observe the initial and mature phases and the beginning of the relaxation phase. The initial phase was characterized by an increase of the south and southwest wind and the Ekman transport, a rise of the seasonal thermocline at the coast and the presence of a cold surface water plume 45-55° towards the left of the coastline. The mature phase was characterized by the presence of strong winds (>10 m-s-1), high mean Ekman transport (>.1,000 m3·s-1 per 1,000 m of coast), a lowering of the temperature (<1.4°C) and dissolved oxygen and an increase of the salinity (>34.4 psu) and nutrients (phosphate >2.0 μM; nitrate >15 μM; silicate >10 μM) at the coastal margin. The declination phase was partially observed, because the wind did not relax enough during the sampling period. However, the surface temperature satellite images on 23 and 24 January, clearly showed a decrease of the area covered with cold upwelled water. The water mass displaced towards the ocean had Subantarctic characteristics and the water mass upwelled to the surface, had Equatorial Subsurface characteristics.