A 240-year stable oxygen and carbon isotopic record in a coral from South Florida; implications for the prediction of precipitation in southern Florida

This study reports on the delta (super 18) O and delta (super 13) C composition of the skeleton from a 240-year-old specimen of Montastraea faveolata growing in Biscayne National Park, South Florida. Annual variations in the delta (super 18) O of the skeleton deposited during the summer months show a bimodal correlation with summer rainfall. During wetter years, the delta (super 18) O of the coral skeleton and the amount of precipitation during the summer months are inversely correlated (r = -0.7) reflecting dilution of the seawater by meteoric water lower in delta (super 18) O. During years in which summer rainfall is less than normal, increases in precipitation are positively correlated with skeletal delta (super 18) O (r = +0.6) reflecting the input of freshwater from the Everglades higher in delta (super 18) O. Based on this correlation the delta (super 18) O record of the coral skeleton suggests that the 19th and 18th centuries have been relatively dry compared to the 20th century. Carbon isotopic compositions of the skeleton are positively correlated with delta (super 18) O, with the minimum in delta (super 13) C occurring several months after the minimum in delta (super 18) O. Since the mid 1930s there has been a decrease in delta (super 13) C of the skeleton. Explanations for this trend may be (1) it reflects the increased input of carbon derived from the destruction of terrestrial ecosystems, (2) its part of a long-term decrease in delta (super 13) C associated with increased addition of fossil fuel-derived CO (sub 2) .