Seasonal archive in a Pliocene clam shell (Mercenaria corrugata) from the Mid Atlantic Coastal Plain (2008)

Undergraduate: Shaena Montanari

Faculty Advisor: Donna Surge
Department: Geology

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The Mid Pliocene Warm Interval (3.2- 2.8 Ma) has been identified by the 2007 Intergovernmental Panel on Climate Change report as a reasonable analog for Earth’s climate in the later 21st century. Sclerochronological analysis of fossil mollusks that deposit seasonal shell growth increments in isotopic equilibrium with ambient water can serve as archives of past climate conditions. A specimen of the extinct hard clam, Mercenaria corrugata, was collected from the Moore House Member of the Yorktown Formation in Virginia along the Middle Atlantic Coastal Plain. Oxygen and carbon isotope ratios (?18O and ?13C) recorded in the M. corrugata shell reflect seasonal changes in the ambient temperature of its habitat over approximately 4 years of growth. Estimated water temperature is close to the modern day average. The translucent increment of shell growth, reflecting an interval of slowed growth, is formed in early spring to early summer, and rapid growth occurs during the optimal temperatures during summer and early fall. The ?13C record also corresponds with the seasonal variation of the ?18O time series; however, we were unable to determine the processes that control this variation due to confounding environmental and metabolic processes. Further study of additional shells from this region may potentially provide insights into the position of the Gulf Stream during the Mid Pliocene Warm Interval and its effect on biogeography, seasonal temperature variation, and climate.