Historical Salinity of Florida Bay Reconstructed from Isotopic Compositions of Corals

Report of statistical analyses, methods, results, assumptions, and calculations of Florida Bay salinity history. The following executive summary details the research carried out by the University of Miami group into the geological evidence of past salinity changes in Florida Bay. The following conclusions have been reached from our study. • Changes in the salinity and temperature of the water in Lignumvitae Basin (Basin 30), situated north of lower and upper Matecumbe Keys, are highly correlated with the oxygen isotopic composition of the coral skeleton allowing the oxygen isotopic composition of the skeleton after removal of the temperature affect, to be used to calculate the salinity of the water. • This improved correlation allows the interpretation of a 160 year record of oxygen isotopes from a coral growing in this basin. The results of this interpretation reveal that a previous study (Swart et al., 1996) underestimated the inter-annual range in salinity, but confirms the interpretation that there have been no long term changes in salinity other than those associated with the construction of the Flagler railway between 1905 and 1912. • A comparison between the oxygen isotopic composition associated with the late 1980s high salinity episode and the remainder of the record indicates that there have seen multiple such events throughout the 160 year history of Florida Bay. • Prior to railway construction, inter-annual variations in salinity were much greater than post construction presumably resulting from a reduction in the exchange of water between the Bay and the reef tract. • Although long-lived corals are only present close to the Florida Keys, smaller, short lived corals are present throughout the Bay. Isotopic records from these small corals generally show similar patterns to the Lignumvitae Basin corals. In particular, the severe salinity episode experienced between 1989 and 1991 is evident in all of the small corals. This supports the idea that corals from Lignumvitae Basin can be used as general indicators of environmental conditions in the remainder of Florida Bay.