TEMPORAL TRENDS AND SPATIAL STRUCTURES OF THE SEA-SURFACE TEMPERATUREIN THE BAY OF BISCAY

A time series spatial grid of sea surface temperature (SST) data provi ded by the archives of Meteo-France and covering the period 1972-1993 was analysed in order to define both the long-term and periodic (mainl y seasonal) components at different locations in the Bay of Biscay. Th e study confirmed the existence of a long-term increasing trend in the SST, but showed that this trend was not homogeneous over the entire a rea. It revealed also that the amplitude of the cyclic components (sum mer-winter differences) is spatially heterogeneous. The south-eastern part of the Bay of Biscay, close to the French-Spanish border, shows t he stronger warming trend (a mean increase of 1.4 degrees C for the pe riod 1972-1993). This trend decreases in the adjacent regions and is n ot statistically significant in the northern part of the bay and the C eltic Sea. The increasing trend was recorded both in winter and summer periods with the winter slopes being slightly higher. The amplitude o f the SST seasonal changes (summer-winter differences) is stronger clo se to the southern French Atlantic coast in the area off the Gironde e stuary. The lowest values were observed in the SW of the bay in the re gion of intense upwelling processes. Finally, the analysis of the main components of this series provides a simple empirical model describin g the time-related changes in the SST. This model could be useful for studies in the field of biological oceanography and in the context of comparative studies. The possible linkage of these observations with c hanges in the structure of ecosystem in this area is also discussed. ( C) Elsevier, Paris.