THE STABLE OXYGEN AND CARBON ISOTOPIC RECORD FROM A CORAL GROWING IN FLORIDA BAY - A 160 YEAR RECORD OF CLIMATIC AND ANTHROPOGENIC INFLUENCE

A 160 year record of skeletal delta(13)C and delta(18)O was examined i n a specimen of the coral Solenastrea bournoni growing in Florida Bay. Variations in the delta(18)O of the skeleton can be correlated to cha nges in salinity while changes in the delta(13)C reflect cycling of or ganic material within the Bay. Based on the correlation between salini ty and skeletal delta(18)O, we have concluded that there has been no l ong term increase in salinity in this area of Florida Bay over the pas t 160 years. Using salinity correlations between the various basins ob tained from instrumental data, we have been able to extend our interpr etations to other parts of Florida Bay reaching similar conclusions. I n contrast to current ideas which have focused on changes in Florida B ay water quality over the past 20-yr history of the Bay as causative i n its decline, we have determined that changes in water quality in thi s basin were already set in motion between 1905 and 1912 by the constr uction of the Florida East Coast Railway from Miami to Key West. The c onstruction of the railway resulted in the restriction of the exchange of water between the Florida reef tract and the Gulf of Mexico causin g Florida Bay to become more eutrophic. Evidence of this process is ob served in the sudden shift to relatively lower delta(13)C values coinc ident with railway construction. Natural events also appear to have in fluenced the water in the Bay. Between 1912 and 1948 frequent hurrican es had the effect of increasing exchange of water between the Bay and reef tract and removing large quantities of organic rich sediments. Ho wever, since 1948 the number of hurricanes affecting the area has decr eased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eut rophic conditions.