TEMPERATURE VARIABILITY IN THE GULF OF CALIFORNIA DURING THE LAST CENTURY - A RECORD OF THE RECENT STRONG EL-NINO

The oxygen isotopic ratio of diatom silica from a box core collected on the eastern slope of the Guaymas Basin (Gulf of California) has been analyzed. This core covers the last 90 years. The isotopic record indicates a progressive and continuous temperature increase of about 8-degrees-C from the end of the last century until 1980 with superimposed, rapid temperature fluctuations of 2 to 4-degrees-C. Although the Gulf of California is not directly under the influence of El Nino, short temperature increases may be associated with the El Nino events described by Quinn et al. (1987). The longer term changes are attributed to a decrease of upwelling intensity linked to weakening of the trade winds in the Northern Hemisphere. Variability of oceanographic conditions is poorly known for the last centuries. In the Gulf of California it has been demonstrated that the sea surface temperature changed during the last three thousand years, in association with a change in the upwelling intensity (Juillet-Leclerc and Schrader, 1987). This study examines more specifically the temperature fluctuations recorded during the last century. Although the Gulf of California is not influenced by EN, it is in the path of the Kelvin wave that propagates along the Californian coast. Due to the particuliar morphology of the Gulf, the effects of El Nino are increased. Both an increase of water temperature and of sea level have been recorded (Baumgartner and Christensen, 1985) for the last ten years. Did such events occur during the whole of the last century? The diatom silica O-18/O-16 ratio from the Gulf of California has been demonstrated to be a good recorder of temperature changes (Juillet-Leclerc and Schrader, 1987). We present here the analysis of a sediment box core, covering the last 90 years, which demonstrates the high variability of temperature of this area, due to fluctuations in upwelling activity and El Nino effects.