Extracting a climate signal from the skeletal geochemistry of the Caribbean coral Siderastrea siderea

Generation of century-long, sub-annually resolved time series of climate variability from massive Atlantic corals has proven difficult for a variety of reasons. Here our objective is to first document that robust proxy climate records can be produced from the slow-growing, massive Atlantic coral Siderastrea siderea and then to generate a proxy climate time series from this heretofore underutilized massive coral. We have generated the first sub-annually (bimonthly) resolved, paired δ18O and Sr/Ca time series from the tropical western Atlantic coral, Siderastrea siderea, from Long Reef in the Dry Tortugas, Florida (~24°33'N, 82°53'W). This record contains a 20-year long calibration window (1973-1992) and a 73-year long verification window (1900-1972), which permits both the quantification of the relationship between coral δ18O-SST and Sr/Ca-SST using an augmented, 1° x 1° gridded SST record and the assessment of the stability and fidelity of these relationships. Both geochemical variables are highly correlated with the augmented instrumental SST record through both the calibration and verification period. The skill of this proxy demonstrates its potential as a continuously growing, long-lived recorder of climate variability for the tropical Atlantic and Intra-American Seas. The relatively slow extension rate of the coral (~4.5 mm yr-1) also suggests the potential for long records of climate variability (>200 years) of the region to be extracted from even modest-sized colonies (~1 m in height).