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 delta D-shell values of samples of freshwater bivalve shells from different streams preserve the relative distribution of delta D values from the water they inhabited over their lifetime (6D(shell)-delta D-water=-145 parts per thousand) after correcting for the contribution of exchangeable hydrogen (similar to 36%) in organic matrix. When 6D(shell) values are compared to the delta O-18 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 delta D value of the organic matrix may serve as an independent proxy for the delta O-18 value of water in paleotemperature equations. (c) 2006 Elsevier B.V. All rights reserved.