Assessment of Porites microatolls for paleothermometry: Calibration for French Polynesia

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2024-05, Vol.642, p.112146, Article 112146
• Main Authors: Farley, Nicholas, Antonioli, Guillaume, Hallmann, Nadine, Camoin, Gilbert, Eisenhauer, Anton, Vella, Claude, Milne, Glenn A., Samankassou, Elias
• Format: Article
• Language: English
• Subjects: Calibration; corals; Environmental Sciences; fossils; French Polynesia; liquid-air interface; Microatoll; palaeogeography; paleoclimatology; paleoecology; Paleothermometry; Porites; prediction; sea level; surface water temperature; uncertainty
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2024.112146

Massive dome-shaped coral Porites are the predominant choice for paleoclimate studies due to their consistent and reliable growth. When growing close to sea level, they become limited in their vertical growth and form so-called ‘microatolls’. Microatolls have not yet been extensively explored for paleoclimate reconstruction. Here, we investigate how reliable modern Porites microatolls are against empirical sea-surface temperature using Sr/Ca, δ18O, Li/Mg and SrU paleothermometry methods on samples from the Society Islands, French Polynesia. Our results show Sr/Ca ratios have the lowest Standard Error of the Inverse Prediction (SEIP) at 0.415 °C (N = 41) with a calibration of Sr/Ca (mmol mol−1) = −0.082 ± 0.006 SST (°C) + 11.256 ± 0.170 and with high reproducibility across multiple corals. The reproducibility of δ18O was less good, with SEIP increasing to 0.829 °C (N = 41). Considering methods directly from the literature, Li/Mg ratio empirically corrected for Sr/Ca had the best balance between bias and precision where no local calibration could be available. This study independently evaluates and confirms the suitability of Porites microatolls from well-flushed environments for paleoclimate studies. Fossil dome-shaped Porites grow anywhere between near-surface and roughly 20 m depths which inherently incorporates uncertainty into any sea surface temperature reconstruction. This uncertainty is significantly reduced for microatolls due to their well-constrained bathymetry. The study represents a fundamental step in paleoclimate research targeting consistently near the water-air interface bringing reliability and, especially when combined with their ability to reconstruct past sea-level changes, microatolls have the potential to be central for future paleoenvironmental studies. •Investigation into the potential of Porites microatolls for SST reconstruction.•Comparison between recent and more conventional coral paleoclimatology methods.•Application of SrU and Li/Mg paleothermometer.•Accuracy and reproducibility of Sr/Ca proved to be the most suitable proxy for SST reconstruction.