A high-resolution calibration of Sr/Ca thermometry using the Caribbean coral Montastraea annularis

A relationship has been established between the Sr/Ca ratio in the skeleton of the scleractinian coral Montastraea annularis and sea surface water temperature in south Florida. In order to obtain this correlation, specimens of Montastraea annularis were transplanted to a site at a local reef where every two to three months throughout a 2‐year period the corals were stained with Alizarin‐red S and where water temperature, which annually ranges between ∼20° and 30°C, was continually monitored. At the end of the experimental period the coral skeleton was sampled at a rate of ∼50 samples per year, each sample corresponding to only around 20 μg of calcium carbonate. For the 2.5‐year period, the Sr/Ca ratio exhibited excellent correlation in the first year (R2 = 0.83; Sr/Ca (mmol/mol) = 10.11 − 0.0452 × SST (°C)), but a rather poorer correlation in the second year (R2 = 0.68; Sr/Ca (mmol/mol) = 10.09 − 0.0406 × SST (°C)). Averaging the data into monthly values for year 1, we determined a relationship of (Sr/Ca (mmol/mol) = 10.165 − 0.0471 × SST (°C). On the basis of the excellent correlation between temperature and Sr/Ca, we feel that this relationship is the most accurate. Discrepancies in the second year are suggested to arise from slight sampling errors relative to the stain lines.