GSA Connects 2021 in Portland, Oregon

Paper No. 188-3
Presentation Time: 2:30 PM-6:30 PM


MINNEBO, Lillian1, WINKELSTERN, Ian Z.1, ZHANG, Jade2, PETERSEN, Sierra2 and LOHMANN, Kyger C.2, (1)Department of Geology, Grand Valley State University, Padnos Hall of Science, 1 Campus Drive, Allendale, MI 49401, (2)Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Ave, Ann Arbor, MI 48109

The islands of Bermuda lie in the North Atlantic Ocean and preserve carbonates from several glacial and interglacial intervals. In the Great Sound, ~110 m long Verrill Island exposes shell lag from the Last Interglacial period (~125,000 years ago). This was broadly a time of similar or slightly warmer climate than today, which can perhaps serve as an analog for near future climate conditions. Here we use sub-annual δ18O analyses of Verrill Island oyster fossils to estimate sea surface temperatures (SST) and seasonality. We also evaluate the suitability of this species for paleoenvironmental reconstruction through comparison with coeval data from other mollusks.

Eight Dendostrea frons oyster shells collected from Verrill Island were sampled along their growth axes for δ18O analysis. We find that, in some cases, the oysters record seasonal variability in temperature and/or water δ18O. As a preliminary temperature calculation, we assumed a constant δ18O water value of +1.0‰, approximating modern δ18O values. Six oysters seem to reflect average growth temperatures and two preserve apparent seasonal temperature curves. The δ18O results range from -1.11 to 0.39‰, roughly corresponding to a temperature change of ~7°C. The limited δ18O range in some shells may be attributable to rapid growth. We report a mean δ18O value of -0.51 ± 0.17‰, corresponding to a temperature of ~23°C. These results are broadly similar to modern SST in Bermuda (~20 to ~28°C) and are on the warmer end of previous local Last Interglacial SST estimates (~8 to ~27°C). However, the data will be refined via ongoing clumped isotope analyses that will better define local water δ18O conditions during shell growth. These data enable more robust interspecies comparison with other records from Bermuda and will contribute to a broader understanding of climate and North Atlantic circulation during the Last Interglacial.