CLUMPED ISOTOPE SCLEROCHRONOLOGY REVEALS COLDER, LOCALLY VARIABLE LAST INTERGLACIAL CONDITIONS IN BERMUDA

The Last Interglacial, a time of globally slightly warmer-than-modern climate, is an important interval to reconstruct past climate because it can serve as a useful reference point for near-future conditions. Recent studies on Last Interglacial/Marine Isotope Stage 5e (MIS 5e) deposits in Bermuda (in the central North Atlantic) have suggested that regional sea surface temperatures (SSTs) were cooler than modern. Prior work has also shown that local effects including coastal groundwater discharge may affect these paleoenvironmental reconstructions.

Here, we expand on the number of sites and species used in previous studies to gain a better picture of MIS 5e climate in Bermuda. We use MIS 5e Dendostrea (oyster) and Glycymeris (clam) shells as paleoenvironmental proxies via clumped (Δ₄₇) and high-resolution conventional stable isotope (δ¹⁸O) analyses. Interpretation of these data is supported by new amino acid racemization age dating results from nine localities around Bermuda, which support an MIS 5e age for all shells analyzed for paleotemperatures.

Localities within the modern Great Sound of Bermuda, Verrill Island and Bird Island, record SSTs similar to modern: 19.1°C to 28.0°C. However, Grape Bay, along the southern shore of the island, records 12.3°C to 18.4°C, much cooler than the Great Sound. The water conditions (δ¹⁸O_water) here are also isotopically lighter. These δ¹⁸O_water and SST conditions agree with previous work at this locality using gastropod shells, suggesting influence from local groundwater discharge on marine water conditions. This may indicate meaningful differences in highly localized environments, with the Great Sound potentially buffered from cooler, groundwater-influenced Grape Bay conditions. The incorporation of clumped isotope analyses emphasizes the importance of multi-locality data for understandings of MIS 5e climate, as interpretations from a single site may support erroneous conclusions.