NOAA/WDS Paleoclimatology - Alina's Reef, Biscayne National Park - Stable Isotope Data

This study reports on the d180 and d13C composition of the skeleton from a 240-year-old specimen of Montastraea faveolata growing in Biscayne National Park, South Florida. Annual variations in the d180 of the skeleton deposited during the summer months show a bimodal correlation with summer rainfall. During wetter years, the d180 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 d180. During years in which summer rainfall is less than normal, increases in precipitation are positively correlated with skeletal d180 (r = +0.6) reflecting the input of freshwater from the Everglades higher in d180. Based on this correlation the d180 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 d180, with the minimum in d13C occurring several months after the minimum in d180. Since the mid 1930s there has been a decrease in d13C 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 d13C associated with increased addition of fossil fuel-derived CO2.