Application of Dual Clumped Isotopes to Last Interglacial Climate of the Persian/Arabian Gulf

The last interglacial warm period and eustatic sea level high stand, MIS 5e, is increasingly used as an analog for near-term effects of anthropogenic global warming. Quaternary sea level fluctuations created complex stratigraphy and diagenetic environments around the Persian/Arabian Gulf, which has impeded the formation of a coherent climate record in this region. Tridacna squamosina, an aragonitic bivalve favored in sclerochronology for its large body and exceptional growth banding, can be found in MIS 5e deposits near Abu Dhabi, UAE. Dual clumped isotopes (paired measurement of Δ47 and Δ48) can produce high quality paleotemperature (and by extension δ18Owater) records from carbonates, including built-in assessment of potential kinetic biases. We collected material from winter and summer growth bands for 10 consecutive years of growth on a single MIS 5e T. squamosina, resampling 6 growth increments to test the effect of frictional heating during drilling (varying drill speed and crushing by mortar and pestle) and bleaching with sodium hypochlorite. Δ47- Δ48 values were indistinguishable from equilibrium regardless of preparation method. Seasonality was not analytically resolvable (< 4°C) and reconstructed δ18Owater indicates normal marine salinity. However, there was an absolute spread of ~20-28°C across all samples, with a decreasing trend in temperatures across 10 years. This range is on the lower end of modern water temperatures in The Gulf but aligns with habitats of modern T. squamosina. Further work on other T. squamosina specimens as well as corals is underway to confirm these relatively cool MIS 5e temperatures.