STABLE OXYGEN ISOTOPIC COMPOSITION OF CORALS FROM THE GULF-OF-GUINEA AS INDICATORS OF PERIODS OF EXTREME PRECIPITATION CONDITIONS IN THE SUB-SAHARA

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 abo ve average precipitation in sub-Sahara Africa. Data presented in this paper show an inverse correlation between precipitation in the Sahel a nd the delta(18)O values of a coral skeletons of the species Siderastr ea spp. collected from the island of Principe in the Gulf of Guinea. T his is opposite to the correlation expected, as previous work has sugg ested that higher sea surface temperatures occur in the Gulf of Guinea during periods of low rainfall in the Sahel. Such an association woul d lead to a positive correlation between Sahel precipitation and skele tal delta(18)O. The explanation for the observed inverse correlation i s that the salinity of the Gulf of Guinea is strongly influenced by th e outflow from the Niger and Congo rivers. These periods of high fresh water input also correlate with periods of higher rainfall in the sub- Sahara and therefore affect the delta(18)O values of the coral skeleto n. The correlation between delta(18)O values of the coral skeleton and temperature in the northern subtropical Atlantic Ocean (r = 0.33), th e magnitude of the dipole (r = 0.45), and the latitudinal position of the inter-tropical convergence zone (r = -0.37) illustrate that the de lta(18)O values in the coral skeleton reflect climate dynamics of the region that affect the precipitation patterns in sub-Sahara Africa.