CO2outgassing continued in an upwelling area off northern Chile during the development phase of El Niño 97-98

continues. High positive SST and sea level anomalies observed off northern Chile since approximately April-May 1997 indicated the onset of El Niño 97-98 in this region. A survey carried out off northern Chile at ca. 23.5°S during July 1997 (austral-winter) showed that the entire water column that feeds the coastal upwelling was anomalously warm and salty compared with non-El Niño winters. Vertical distributions of pH, total alkalinity, calculated fCO₂ (fugacity of CO₂) and O₂ suggested that below 20m depth the coastal water column was more oxygenated and with lower fCO₂ than the colder water that occupied this stratum during the non-El Niño years (e.g. July 1989). Nevertheless the entire water column remained largely CO₂ supersaturated during July 1997.

During the study period as well as during others winters (i.e. 1972, 1983) when the sea temperature anomalies were strongly positive (> +2°C) the main portion of the oxycline remained over 100m depth, consequently low oxygen and CO₂ rich water (oxygen-poor waters are invariably CO₂ supersaturated) can reach the surface due events of enhanced upwelling forcing. In fact under active upwelling during july 1997 we found coastal fCO₂ levels between 400-600µatm. We conclude that the coastal CO₂ outgassing continues during El Niño periods as long as coastal upwelling