MODERN AND HOLOCENE SST RECORDS FROM THE CORAL MONTASTRAEA FAVEOLATA, DRY TORTUGAS NATIONAL PARK

This study examined the variations in the ratio of strontium to calcium (Sr/Ca) from modern and fossil Montastraea faveolata coral cores from the Dry Tortugas National Park (DTNP, centered on 24.7°N, 82.8°W) in the Gulf of Mexico. A modern coral core (collected in 2008) was micro-sampled with a computer-driven milling device, obtaining at least 15 samples per year. Sr/Ca variations were calibrated (r = -0.97) with a 12-year local sea-surface temperature (SST) record from NOAA National Data Buoy Center (C-MAN) stations PLSF1 and DRYF1 using maximum and minimum temperatures (Sr/Ca = -0.0385 SST + 10.188). This resulting calibration was used to generate a 47-year modern (1961-2008) Sr/Ca proxy record of SST variability. Modern annual Sr/Ca cycles range in amplitude between ~0.4 and 0.6 mmol/mol, equating to an ~10-15°C seasonal amplitude, which is consistent with available local instrumental records. Winter months demonstrate the highest variability, with a cool interval in the early 1970s. Summer maxima tend to be more stable: most summer SST maxima were 29 +/- 1°C.

To test the potential of Sr/Ca from Montastraea faveolata as a SST proxy in paleoclimate studies, we sampled a Holocene (~6Ka) M. faveolata specimen recovered from a wire-line rotary core from DTNP, using the same high-resolution sampling methods utilized on the modern coral. The Holocene coral Sr/Ca displayed distinct annual cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and the resulting temperature estimates were similar to those of the modern record. Thus, Sr/Ca variations in M. faveolata have high potential as a reliable proxy for modern and Holocene SST reconstructions.