Variable Aquifer Discharge and Cooler Climate in Bermuda during the Last Interglacial Revealed by Subannual Clumped Isotope Analysis

Abstract:

Faunal analog reconstructions suggest that Last Interglacial (MIS 5e) sea surface temperatures (SSTs) were regionally variable in the Atlantic sector. Here we describe new and revised clumped isotope measurements of Cittarium pica fossil shells indicating cooler than modern temperatures in Bermuda during the Last Interglacial, consistent with previous studies. New subannual-resolution clumped isotope data reveal large variations in δ¹⁸O_w out of phase with seasonal temperature changes (i.e. isotopically lighter δ¹⁸O_w values in winter). Supported by modern δ¹⁸O_w measurements, we suggest these large variations in coastal δ¹⁸O_w were driven by seasonally variable freshwater discharge from a subterranean aquifer beneath the island_. Taken together, our results emphasize the importance of δ¹⁸O_w in controlling carbonate δ¹⁸O, suggesting that typical assumptions of seasonally constant δ¹⁸O_w fails at this site and should be made more cautiously in other nearshore settings.