Climatic trends in continental shelf waters off Ghana and in the Gulf of Guinea, 1963-1992

Using time series analyses, some physical parameters of the continental shelf waters of the Gulf of Guinea were examined. Analysis of coastal sea surface temperatures from Ghana and Ivory Coast, and offshore sea surface temperatures from the Gulf of Guinea clearly shows spatial and inter-annual patterns of cooling in coastal waters of West Africa. The behaviour of the decomposed trend of coastal and offshore sea surface temperatures, sub-surface: temperature measured at 100 m depth off Ghana and salinity showed that the observational period (1963-1992) could be divided into three climatic periods: the period before 1972, from 1972 to 1982, and the period after 1982. In the first period, sea surface temperature at both coastal and offshore areas and bottom temperature declined and coastal salinity was relatively low. The second period was a cold one with less than average sea surface and sea bottom temperatures. The mixed layer was narrow with the thermocline remaining shallower than its: long-term average position. Coastal and bottom salinity (measured at the 100 m depth) were relatively high but the seasonal variation was minimal. This period of significant change in the physical components of the ecosystem of the Ghanaian shelf waters has hitherto not been documented in the literature. In the final phase, temperatures were high, and salinity was low and erratic. The observed localised environmental changes are consistent with global changes in the Gulf of Guinea and possibly in the tropical Atlantic basin. (C) 2001 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.