South Atlantic Multi-Site Calibration of Coral Oxygen Isotope Paleothermometer

Abstract

Coral-based stable oxygen isotopes (δ¹⁸O) have been used as a proxy for sea surface temperature (SST) since the 1970s, and δ¹⁸O–SST calibration studies have been fundamental to assure robust and faithful SST reconstructions. Paleoclimatic studies based on corals from the tropical western South Atlantic (TWSA) are scarce, and the available coral species need to be calibrated to improve climate and environmental reconstructions. Siderastrea stellata, a slow-growing coral, is a potential species to be explored as a coral archive in the TWSA. We provide the first multi-site δ¹⁸O–SST calibration for the coral S. stellata from three locations at the TWSA: Todos os Santos Bay, Tamandaré and the Rocas Atoll. Pseudo-coral δ¹⁸O calculations derived from gridded SSS and SST show that the contributions of SSS and SST to coral δ¹⁸O are expected to be different at each site. Weighted least squares linear regressions performed between the δ¹⁸O and SST generated the following calibrations equations: δ¹⁸O = −0.18 (±0.02) × SST (°C) + 1.90 (±0.47) for Todos os Santos Bay; δ¹⁸O = −0.18 (±0.02) × SST (°C) + 1.54 (±0.67) for Tamandaré; and δ¹⁸O = −0.16 (±0.03) × SST (°C) + 1.24 (±0.71) for the Rocas Atoll. The δ¹⁸O-SST sensitivity of S. stellata from the TWSA is similar to that of other slow-growing species of the genus and consistent with the expected δ¹⁸O-SST sensitivity of other species reported in the literature. These calibrations will allow future SST reconstructions based on δ¹⁸O records from sub-fossil and fossil S. stellata, an abundant species in the TWSA.