Cooling climate across last interglacial high stands on San Salvador and Great Inagua, The Bahamas

Abstract The last interglacial (LIG) is the last time global climate was about as warm as today, with global sea‐levels several metres higher. The LIG probably had a reduced latitudinal temperature gradient, with warmer poles and cooler tropics than today. Well‐constrained records from low latitudes can test this overall model. We used bivalve shells sampled from six localities thought to expose the LIG age Cockburn Town Member of the Grotto Beach Formation on both San Salvador and Great Inagua Islands, The Bahamas. Previous work described two LIG depositional intervals: older ‘Reef I’ and younger ‘Reef II’, separated by a disconformity. New amino acid racemisation (AAR) data were used to date each locality in this context and clumped isotope palaeothermometry was used to reconstruct LIG temperatures and the isotopic composition of sea water. AAR data are described from six sites: four with similar AAR values to the well‐dated Reef II Cockburn Town site, one Reef I age site on Great Inagua and one distinctly younger outcrop on San Salvador previously thought to be LIG age that may be MIS 5a. All LIG shells record cooler than modern conditions. The Δ 47 thermometry shows that the Reef I‐age shell population preserves the warmest mean temperature (25 ± 2°C) and most positive water δ 18 O values (+0.7 ± 0.4‰) across all sites. This contrasts with cool mean temperatures (~21–23°C) and fresher water δ 18 O values (−0.5 to +0.6‰) found from Reef II populations. Regional glacial isostatic adjustment through the LIG would have resulted in peak sea levels that post‐dated peak LIG temperatures. It is suggested that apparent cooler temperatures of Reef II do not reflect peak LIG temperatures but instead document the beginning of cooling into MIS 5d. Comparison with Δ 47 data from Bermuda supports a reduced latitudinal gradient throughout the LIG.