Stable oxygen isotopic composition of corals from the Gulf of Guinea as
indicators of periods of extreme precipitation conditions in the sub-Sahara
Peter K. Swart,1 Kathy S. White,1 David Enfield,2 Richard E. Dodge,3 and Peter Milne4
Abstract. Stable oxygen isotopic analyses of scleractinian coral skeletons from the Gulf of Guinea in the eastern Atlantic reveal that the corals from this region can be used to identify periods of severe drought and above average precipitation in sub-Sahara Africa. Data presented in this paper show an inverse correlation between precipitation in the Sahel and the d18O values of a coral skeletons of the species Siderastrea spp. collected from the island of Principe in the Gulf of Guinea. This is opposite to the correlation expected, as previous work has suggested that higher sea surface temperatures occur in the Gulf of Guinea during periods of low rainfall in the Sahel. Such an association would lead to a positive correlation between Sahel precipitation and skeletal d18O. The explanation for the observed inverse correlation is that the salinity of the Gulf of Guinea is strongly influenced by the outflow from the Niger and Congo rivers. These periods of high freshwater input also correlate with periods of higher rainfall in the sub-Sahara and therefore affect the d18O values of the coral skeleton. The correlation between d18O values of the coral skeleton and temperature in the northern subtropical Atlantic Ocean (r= -0.34), the magnitude of the dipole (r= -0.45), and the latitudinal position of the intertropical convergence zone (r= -0.37) illustrate that the d18O values in the coral skeleton reflect climate dynamics of the region that affect the precipitation patterns in sub-Sahara Africa.