Evidence for a Sea Level Fall During the Last Interglacial Highstand on West Caicos, Turks and Caicos Islands

Abstract Reconstruction of ancient sea level during the Late Pleistocene Marine Isotope Stage 5e (MIS 5e), from ∼129 to 116 ka, has the potential to improve the accuracy of future global sea level projections by providing a key benchmark for model calibration during a past warm period. Shallow‐water carbonate exposures comprising the tectonically stable Bahamas and Turks and Caicos Islands contain a regional unconformity that suggests MIS 5e sea level variability. It is not yet fully understood whether this intra‐MIS 5e unconformity was formed under subaerial or submarine conditions. The current study applies next generation sedimentologic, stratigraphic and petrographic analyses across the intra‐MIS 5e erosional unconformity exposed at four locations on West Caicos to reconstruct the conditions in which it formed. The unconformity is characterized with field mapping and digital terrain models, combined with U‐Th coral dating from previous studies. Marine and meteoric diagenetic alteration events were determined by integrating field observations and high‐resolution brightfield and autofluorescence microscopy to compile a comprehensive paragenetic sequence of the intra‐MIS 5e unconformity. Results indicate the erosional unconformity coincided with a rapid 1–3 m sea level fall resulting in beveled in situ coral heads and spatially constrained meteoric diagenesis. Current models of solar insolation and global‐scale ice sheet dynamics currently do not predict an intra‐MIS 5e sea level fall or associated climatic fluctuations. Illuminating the magnitude and timing of an intra‐MIS 5e sea level fall will provide better constraints on numerical models that link ice sheet collapse and climate change.