STABLE ISOTOPES OF CAPE VERDE SCLERACTINIA SHOW LINKS TO TROPICAL NORTH ATLANTIC CLIMATE INDICES

It has been shown that Atlantic sea surface temperature (SST) influences the rainfall of widespread regions in both the Americas and Africa. In addition, some teleconnections have been shown between Atlantic SST and Pacific SST anomalies. Major climate indices in the Atlantic includes the AMO (Atlantic Multidecadal Oscillation), NAO (North Atlantic Oscillation), the NATL (North sub-tropical Atlantic Oscillation), and the SATL (South sub-topical Atlantic Oscillation). The Cape Verde Islands are within the zone of highest correlation (r > 0.80) for the NATL. These dry, volcanic islands lie off the west African coast at about 16° N, and four species of zooxanthellate scleractinia are present. Of these corals, the species Siderastrea radians forms slabs of upto 24 cms in thickness. Combined with a relatively low rate of extension the specimens are between 50 and 200 years in age. We have collected several colonies from Cape Verde which have been slabbed, x-rayed, and sampled for d¹⁸O, d¹³C, Sr/Ca, Ba/Ca, and fluorescence. Sclerochronology dates one of these corals back as far as 1938 with an accuracy of ± 0.5 yr. During the time frame from 1938-1999, the oxygen isotopic composition show a strong correlation with the most recent drought in the Sahel region of Africa (11°-18° N) which began about 1970. This Cape Verde coral also shows a negative correlation within the same period with the NATL and a positive correlation within that period with Sahel rainfall and the AMO. The history of the this particular coral is too short to accurately elucidate such signals as the 65-80 year cycle of the AMO, but ongoing investigation with older specimens promises to show other connections between stable isotope records in Cape Verde corals and tropical Atlantic SST and nearby terrestrial climates.