Sr/Ca Proxy Sea-Surface Temperature Reconstructions from Modern and HoloceneMontastraea faveolataSpecimens from the Dry Tortugas National Park, Florida, U.S.A.

Abstract

Flannery, J.A. and Poore, R.Z., 2013. Sr/Ca proxy sea-surface temperature reconstructions from modern and Holocene Montastraea faveolata specimens from the Dry Tortugas National Park In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 20–31, Coconut Creek (Florida), ISSN 0749-0208.Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ∼6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer- driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961–2008) and a 7-year Holocene (∼6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ∼0.3 and 0.5 mmol/mol. The amplitude of ∼0.3 to 0.5 mmol/mol equates to a ∼10–15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s.The Holocene (∼6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ∼0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ∼7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.