Seasonal and wind-induced variability of Sea Surface Temperature patterns in the Gulf of Cádiz

The evolution of thermal structures in the Gulf of Cádiz is analysed with a set of 325 weekly composite Sea Surface Temperature (SST) images derived from NOAA–AVHRR sensor, and covering a time span of 7 years, from 1993 to 1999. A spatial Empirical Orthogonal Function (EOF) analysis has been performed in order to identify the main SST spatial patterns. The first EOF mode explains 60% of the temperature variance of the images, and shows a quasi-permanently warmer than the mean region in the southern part of the area of study. The second mode (13% of variance), has a strong temporal variability, and is the main responsible for the cooling and warming of the shelf waters in southwestern Iberia. These two modes explain together most of the seasonal variability of SST over the basin, particularly the variation and strength of the upwelling area located southeast of Portugal. The third mode explains 6% of variance and is well correlated with the local zonal wind. Two wind-induced upwelling can be clearly identified in this mode. The first one, located at the southwestern end of the Strait of Gibraltar, takes place during easterlies events. The second one, related to westerlies, is located to the east of Cape Santa María, and is associated with a southeastward transport of cold surface waters from that Cape.