Department of Earth System Science

A14C records are reported for post-bomb corals from three sites in the tropical Atlantic Ocean. In corals from 18°S in the Brazil Current, A14C values increased from ca. -58% in the early 1950s to +138%o by 1974, then decreased to 110% by 1982. Shorter records from 8°S off Brazil and from the Cape Verde Islands (17°N) showed initially higher A14C val- ues before 1%5 than those at 18°S, but showed lower rates of increase of A14C during the early 1960s. There is general agree- ment between the coral results and &4C of dissolved inorganic carbon (DIC) measured in seawater previously for locations in the tropical Atlantic Ocean. Al4C values at our tropical ocean sites increased at a slower rate than those observed previously in the temperate North Atlantic (Florida and Bermuda), owing to the latter's proximity to the bomb 14C input source in the northern hemisphere. Model results show that from 1960-1980 the Cape Verde coral and selected DIC A14C values from the North Equatorial Current agree with that calculated for the North Atlantic based on an isopycnal mixing model with a constant water mass renewal rate between surface and subsurface waters. This is in contrast to A14C values in Bermuda corals that showed higher post-bomb values than those predicted using a constant water mass renewal rate, hence indicating that venti- lation in the western north Atlantic Ocean had decreased by a factor of 3 during the 1960s and 1970s Druffel 1989).