Seasonally Variable Aquifer Discharge and Cooler Climate in Bermuda During the Last Interglacial Revealed by Subannual Clumped Isotope Analysis
Jade Z. Zhang, Sierra Petersen, Ian Z. Winkelstern, Kyger C. Lohmann
Abstract
Abstract Faunal analog reconstructions suggest that Last Interglacial (MIS 5e) sea surface temperatures were cooler around Bermuda and in the Caribbean than modern climate. Here we describe new and revised clumped isotope measurements of Cittarium pica fossil shells supporting previous findings of cooler than modern temperatures in Bermuda during the Last Interglacial. We resolve temperature and δ 18 O w differences between two closely located and apparently coeval sites described in Winkelstern et al. (2017), https://doi.org/10.1002/2016pa003014 through reprocessing raw isotopic data with the updated Brand/IUPAC parameters. New subannual‐resolution clumped isotope data reveal large variations in δ 18 O w out of phase with seasonal temperature changes (i.e., lower δ 18 O w values in winter). Supported by modern δ 18 O w measurements identifying similar processes occurring today, we suggest past variations in coastal δ 18 O w were driven by seasonally variable freshwater discharge from a subterranean aquifer beneath the island. Taken together, our results emphasize the importance of δ 18 O w in controlling carbonate δ 18 O, and suggest that typical assumptions of constant δ 18 O w should be made cautiously in nearshore settings and can contribute to less accurate reconstructions of paleotemperature.