Bivalve shells have been used in a number of paleoclimate and paleoenvironment studies. In order to investigate oxygen and carbon isotope fractionation between bivalve aragonite and host water, a one year monitoring experiment was conducted. Temperature, δ18OWATER and δ13CDIC were measured every week from January 2006 to January 2007. These data were used to calculate expected δ18O and δ13C equilibrium values to compare to measured shell values. At the end of the monitoring experiment, living bivalves (Corbicula fluminea) were collected and sampled for stable isotope analysis (δ18Oar and δ13Car). Comparison of shell δ18O with expected values revealed precipitation of δ18O in equilibrium with the ambient environment from early spring to early fall. Winter values were not recorded due to winter growth cessation. Cooler temperatures seem to cause cessation of growth, suggesting that a threshold temperature may control the onset and cessation of growth. Shell δ13C are more negative than predicted δ13C values, and we observed that all the specimens showed a trend of lower δ13C values with increasing age, this suggests that the incorporation of metabolic carbon is the cause of the negative offset in shell δ13C. The variable offset from equilibrium δ13C values precludes the direct use of Corbicula fluminea shell in the study of the δ13CDIC in ancient bodies of water.
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