Radiocarbon measurements of hermatypic corals from four sites in the Cariaco Basin and Gulf of Mexico were made to estimate the marine 14C reservoir age (R) for this region and to reconstruct the D14C of surface waters during the pre- to post-nuclear bomb transition. Corals cores were obtained using a diver-operated underwater hydraulic drill and cut into ~5mm thick slabs for analysis. Coral skeletal material from the Flower Garden Banks (northern GOM continental shelf), Veracruz, Mexico, and two reefs from the Cariaco Basin, Venezuela (one within the basin proper and one just outside of the basin) were analyzed. All samples are of the same species, grew in the upper 20m of the water column and were alive when cored. Coral chronology was estimated using a combination of x-radiography to determine annual high/low density bands and oxygen isotope stratigraphy. Sub-annual and annual samples from 1943-1996 were milled and radiocarbon composition was determined using accelerator mass spectrometry.
Due to the production of 14C as a consequence of nuclear weapons atmospheric tests in the 1950s and 1960s, the D14C of the coral skeletal material began increasing in the late 1950s and reached a maximum in the mid 1970s at each site. The average maximum D14C for the Gulf of Mexico and Cariaco Basin corals is 162 per mil and 127 per mil, respectively. We compared our data with previously published coral D14C data from the Gulf of Mexico, Caribbean Sea and Brazil (Druffel, 1980, 1996). The average maximum D14C for the Gulf of Mexico/Caribbean sites is 155 per mil while the maximum for the Brazil site is 137 per mil. This suggests that over the time period analyzed, the average annual D14C in the Cariaco Basin may be dominated by the advection of southern hemisphere surface water. In addition, exchange of CO2 from the atmosphere to the surface ocean and regional upwelling may influence the D14C. Thus, the current thoughts regarding the dominant controls on the reservoir age of the Cariaco Basin may require modification.
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