Spatial and Temporal Robustness of Sr/Ca-SST Calibrations in Red Sea Corals: Evidence for Influence of Mean Annual Temperature on Calibration Slopes

Sr/Ca ratios recorded in the aragonite skeleton of massive coral colonies are commonly used to reconstruct seasonal- to centennial-scale variability in sea surface temperature (SST). While the Sr/Ca paleothermometer is robust in individual colonies, Sr/Ca-SST relationships between colonies vary, leading to questions regarding the utility of the proxy. We present biweekly-resolution calibrations of Sr/Ca from five Porites lobata/lutea corals to satellite SST across 10° of latitude in the Red Sea to evaluate the Sr/Ca proxy across both spatial and temporal scales. SST is significantly correlated with coral Sr/Ca at each site, accounting for 69-84% of Sr/Ca variability (p<<0.01). Inter-colony variability in Sr/Ca-SST sensitivities reveals a latitudinal trend, where calibration slopes become shallower with increasing mean annual temperature. Mean annual temperature is strongly correlated with the biweekly-resolution calibration slopes across five Red Sea sites (r2=0.88, p=0.05), while also correlating significantly to Sr/Ca-SST slopes for 33 Porites corals from across the entire Indo-Pacific region (r2=0.26, p<0.01). Although interannual summer, winter and mean annual calibrations for individual Red Sea colonies are inconsistently robust, combined multi-coral calibrations are significant at summer (r2=0.53, p<<0.01), winter (r2=0.62, p<<0.01), and mean annual timescales (r2=0.79, p<<0.01). Our multi-coral, multi-site study indicates that the Sr/Ca paleothermometer is accurate across both temporal and spatial scales in the Red Sea, and also potentially explains for the first time variability in Sr/Ca-SST calibration slopes across the Indo-Pacific region. Our study provides strong evidence supporting the robustness of the coral Sr/Ca proxy for examining seasonal to multi-century variability in global climate phenomena.

Citation

Murty SA, Bernstein WN, Ossolinski JE, Davis RS, Goodkin NF, et al. (2018) Spatial and Temporal Robustness of Sr/Ca-SST Calibrations in Red Sea Corals: Evidence for Influence of Mean Annual Temperature on Calibration Slopes. Paleoceanography and Paleoclimatology 33: 443–456. Available: http://dx.doi.org/10.1029/2017pa003276.

Sponsors

We thank the crew of the M/V Dream Island for help in the collection of the coral cores. This study was funded by the King Abdullah University of Science and Technology (KAUST Award Nos. USA 00002 and KSA 00011) and the U.S. National Science Foundation (NSF Award No. OCE-1031288) grants to K. Hughen. This research was also supported by the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centres of Excellence initiative and by the National Research Foundation Singapore under its Singapore NRF Fellowship scheme (National Research Fellowship Award to N. Goodkin, NRFF-2012-03). The coral Sr/Ca data generated in this study can be found in Table S5 and are archived at the NOAA NCDC World Data Center for Paleoclimatology at http://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets.