Isothermal Thermoluminescence Dating of Coral Reef Calcite: Implications for Sea-Level Change

Reconstructing past sea-level changes is critical in Quaternary science. On remote oceanic reefs, aragonite-to-calcite alteration occurs during subaerial exposure, directly recording the timing of sea-level fall. U–Th dating of coral calcite is challenging due to open-system issues. However, following calcite formation, the accumulated thermoluminescence (TL) signal can date the initial subaerial exposure event. This study pioneers the application of isothermal thermoluminescence (ITL) dating of reef calcite from the Xisha Islands, South China Sea. ITL single-aliquot regenerative-dose protocol improved the precision of equivalent dose measurement. By integrating dose rate simulation within a Bayesian framework constrained by U–Th ages, we obtained ITL ages of 127.0 ± 8.0 and 138.5 ± 1.5 ka for two reef core samples, dating sea-level lowstands to late Marine Isotope Stage 6. Our results demonstrate that ITL dating of reef calcite enables the high-resolution chronostratigraphic reconstruction of sea-level sequences back to at least 1.5 million years ago.