Stable isotope composition of the modern freshwater bivalve Corbicula fluminea

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, delta O-18(WATER) and delta C-13(DIC) were Measured every week from January 2006 to January 2007. These data were used to calculate expected delta O-18 and delta C-13 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 (delta O-18(ar) and delta C-13(ar)). Comparison of shell delta O-18 with expected values revealed precipitation of delta O-18 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 delta C-13 are more negative than predicted delta C-13 values. and we observed that all the specimens showed a trend of lower delta C-13 values with increasing age, this suggests that the incorporation of metabolic carbon is the cause of the negative offset in shell delta C-13. The variable offset from equilibrium delta C-13 values precludes the direct use of Corbicula fluminea shelf in the study of the delta C-13(DIC) in ancient bodies of water.