d13C of fluvial mollusk shells (Rhône River): A proxy for dissolved inorganic carbon?
Limnol. Oceanogr., 48(6), 2003, 2186-2193 | DOI: 10.4319/lo.2003.48.6.2186
Abstract: The relationship between the 
13C of dissolved inorganic carbon (DIC) and modern mollusk aragonite from rivers was calibrated for the purpose of reconstructing DIC paleochemistry from the shell record. The 13C values of aragonitic bivalves (Dreissena polymorpha, Corbicula fluminea), prosobranch gastropods (Bithynia tentaculata, Theodoxus fluviatilis, Viviparus viviparus), and an air-breathing pulmonate gastropod (Limnea auricularia) were analyzed from several locations on the Rhône River (-13.7‰ to -6.0‰) and its major tributary, the Saône River (-11.4‰ to -10.2‰). The 13CDIC varied from -11.5‰ to -7.5‰, and the 13C of particulate inorganic matter (POM) varied from -31.7‰ to -25.4‰. At a given site, the 13C of all species except the pulmonate were within 1‰ of each other. Whole-shell 13C correlated positively with 13CDIC, with a slope close to unity. Bioaragonite–DIC fractionations were 0–1.5‰ for bivalves and 0–2.7‰ for gastropods (excluding the pulmonates). Applying these fractionations, bivalves that live in open water are a reliable proxy, monitoring the average 13CDIC value to within its natural ~2‰ temporal variation within the growth period. For the suspension feeders (bivalves) using POM as a food source, the 13C of whole shells and bulk POM indicated that the incorporation of carbon derived from respiratory sources lay in the range 10–30%. Fine-scale analyses of growth increments of C. fluminea could not be related simply to 13CDIC because metabolic and seasonal variations in 13CDIC produced similar isotopic fluctuations (
2.5‰).