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(18)O and delta(13)C composition of the skeleton from a 240-year-old specimen of Montastraea faveolata growin g in Biscayne National Park, South Florida. Annual variations in. the delta(18)O of the skeleton deposited during the summer months show a b imodal correlation with summer rainfall. During wetter years, the delt a(18)O of the coral skeleton and the amount of precipitation during th e summer months are inversely correlated (r = -0.7) reflecting dilutio n of the seawater by meteoric water lower in delta(18)O. During years in which summer rainfall is less than normal, increases in precipitati on are positively correlated with skeletal delta(18)O (r = +0.6) refle cting the input of freshwater from the Everglades higher in delta(18)O . Based on this correlation the delta(18)O record of the coral skeleto n suggests that the 19th and 18th centuries have been relatively dry c ompared to the 20th century. Carbon isotopic compositions of the skele ton are positively correlated with delta(18)O, with the minimum in del ta(13)C occurring several months after the minimum in delta(18)O. Sinc e the mid 1930s there has been a decrease in delta(13)C of the skeleto n. Explanations for this trend may be (1) it reflects the increased in put of carbon derived from the destruction of terrestrial ecosystems, (2) its part of a long-term decrease in delta(13)C associated with inc reased addition of fossil fuel-derived CO2.