A preliminary assessment of oxygen isotope fractionation and growth increment periodicity in the estuarine clam Rangia cuneata |
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| Authors: | C Fred T Andrus Kelley Whatley Rich |
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| Institution: | 1. Department of Geological Sciences, University of Alabama, Tuscaloosa, AL, 35487, USA
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| Abstract: | Rangia cuneata is an upper estuarine clam common in the coastal regions of the Gulf of Mexico. Limited data exist regarding oxygen isotope fractionation and microstructural increment periodicity in this species. As these clams were recently identified as an invasive species in other regions, such data may be useful for environmental management purposes. Additionally, the shell of this clam is common in archeological middens, and thus may serve as a paleoenvironmental proxy. In order to assess these aspects of the species’ natural history, samples were collected from the upper Mobile Bay, Alabama, USA. A stable oxygen isotope profile was generated from one of these valves, and compared to growth increments seen in thin section. Time-series water temperature data from near the collection site were used to construct idealized models of oxygen isotope variation, assuming equilibrium fractionation, constant shell growth, and stable water δ18O values. Comparison of the modeled and measured data suggest the shell was precipitated in, or near oxygen isotope equilibrium with ambient water, and that the microstructural increments in the shell were precipitated in response to tidal cycles. |
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