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