The relationship between the hydrogen and oxygen isotopes of freshwater bivalve shells and their home streams

Recent technical advances have facilitated the analysis of microgram-size samples of mollusk shell for the hydrogen isotope composition of the organic matrix. Our results suggest that these data are meaningful as the δDshell values of samples of freshwater bivalve shells from different streams preserve the relative distribution of δD values from the water they inhabited over their lifetime (δDshell − δDwater = − 145‰) after correcting for the contribution of exchangeable hydrogen (∼ 36%) in organic matrix. When δDshell values are compared to the δ18O values of the mineral fraction of the shell (CaCO3 as aragonite), they plot along a line that reflects the isotopic composition of the waters in which the bivalves lived. This relationship is potentially useful for paleoenvironmental reconstructions because the δD value of the organic matrix may serve as an independent proxy for the δ18O value of water in paleotemperature equations.