COMPARING SEASONAL SEA SURFACE TEMPERATURES FROM OXYGEN ISOTOPE RATIOS AND CLUMPED ISOTOPES RECORDED IN MERCENARIA SPP. SHELLS DURING THE PLIO-PLEISTOCENE

Seasonal sea surface temperature (SST) reconstructions from deep-time archives can potentially provide insight into the nature of the climate system on sub-annual scales during critical climate states such as the Mid Piacenzian Warm Interval (MPWI) and subsequent early Pleistocene cooling. Traditional oxygen isotope (δ¹⁸O) measurements in biogenic carbonates have been the dominant seawater (sw) temperature proxy in marine archives but can be complicated by assumptions made to constrain δ¹⁸O_sw values. Clumped isotope geochemistry (∆₄₇) shows promise as a novel paleothermometer, as it does not rely on constraining the δ¹⁸O_sw value. In this study, we validate that Mercenaria shells do not require a species-specific ∆₄₇ paleotemperature calibration by comparing ∆₄₇ values recorded by modern Mercenaria from coastal NC and recorded water temperature to the universal ∆₄₇ paleotemperature calibration. We then compared seasonal SSTs during the MPWI, subsequent early Pleistocene cooling, and today using δ¹⁸O_shell values to seasonal SSTs derived from ∆₄₇ values. Local maxima and minima within the δ¹⁸O_shell timeseries were targeted to collect 1.5-2mg of carbonate powder for ∆₄₇ analysis to capture the largest range of recorded temperature. Oxygen isotope ratios record average summer and winter temperatures of 28±1°C and 18±2°C during the MPWI, 22±1°C and 11±3°C during the early Pleistocene, and 30±4°C and 15±7°C in modern shells. Preliminary analyses were conducted for 3 annual maxima/minima pairs (n = 6 per shell) on 3 modern shells. Values of ∆₄₇ range from 0.645‰ to 0.733‰ and SST estimates based on available calibration studies of inorganic and organic carbonates were compared to SST estimates from δ¹⁸O_shell values. Based on these preliminary data, results suggest that ∆₄₇-based temperature estimates from M. mercenaria are consistent with both observational data and existing δ¹⁸O calibration estimates.