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Stable Isotope and Sr/Ca Profiles From the Marine Gastropod Conus ermineus: Testing a Multiproxy Approach For Inferring Paleotemperature and Paleosalinity

¹ Texas A&M University, Department of Geology and Geophysics, College Station, Texas 77843, USA
² Rutgers University, Institute of Marine and Coastal Sciences, New Brunswick, New Jersey 08901, USA
³ Rutgers University, Department of Geological Sciences, New Brunswick, New Jersey 08901, USA
⁴ University of Texas, Brownsville, Department of Biological Sciences, Brownsville, Texas 78520, USA;
⁵ Cardiff University, School of Earth, Ocean, and Planetary Sciences, Cardiff CF10 3YE, UK e-grossman{at}tamu.edu

This study tests the fidelity of shallow-water gastropod skeletons as multiproxy archives of paleoenvironmental change by comparing isotopic and trace-metal analyses of specimens of Conus ermineus. Four adult specimens were collected live from Stetson Bank in the northwestern Gulf of Mexico during the summer of 2003. Shells were sampled along axes of growth to produce time-series profiles spanning up to 8 years. ¹⁸O and Sr/Ca profiles show seasonal cyclicity modified by fast summer and slow winter shell growth. The profiles were combined to estimate paleosalinity. This yields variable results that overestimate salinity range; nevertheless, annual salinity minima and maxima are still evident. The overestimates are attributed to interspecimen Sr/Ca variability and error in the ¹⁸O_sw-salinity regression. Profiles of ¹³C show seasonal variation superimposed on a decreasing ontogenetic trend, the latter ascribed to decreasing metabolic efficiency also reflected by an ontogenetic increase in Sr/Ca. Seasonal ¹³C variation reflects changes in the ¹³C of dissolved inorganic carbon (¹³C_DIC). Salinity and ¹³C_DIC at Stetson Bank strongly correlate (R² = 0.80, p < 0.0001), and shell ¹³C minima coincide with local salinity minima following times of peak river discharge. These ¹³C minima terminate during annual shelf current reversals. Low-salinity waters directly account for less than half the variability in shell ¹³C but enhance summer stratification and trap respired CO₂ from sediment pore waters. Specimens from this study show mean ¹³C values 1 lower than C. ermineus collected from Stetson Bank in 1971, reflecting the decrease in ¹³C_DIC from anthropogenic CO₂.

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