CARBON AND OXYGEN ISOTOPE ANALYSIS OF MODERN FRESHWATER MOLLUSK SHELLS: APPLICATIONS FOR CLIMATE RECONSTRUCTION

Stable carbon and oxygen isotope profiles from modern bivalve shells can be used to reconstruct hydrologic changes in freshwater bodies. Potamilns alatus and Lampsilis sp. from the Cannon River, southeastern Minnestoa, display clear seasonal growth banding profiles that were analyzed for d 18O and d 13C content. The d 18O recorded in the Potamilns alatus shell is mainly controlled by seasonal fluctuations in the hydrologic conditions of the Cannon River as demonstrated by the persistent variation between seasonally deposited growth bands. d 13C signatures from the Potamilns alatus demonstrate less coherent variations and are more highly dependent on individualized metabolic processes, masking possible environmental influences. Using d 18O signatures of seasonal growth bands, shells of the freshwater mussel Potamilns alatus offer a high-resolution record of temperature variation on seasonal to multi-year time scales. In contrast, the Lampsilis sp. shell studied shows little variation on any time scale and may be less useful as a paleoclimate indicator. Changes in growth band d 18O in Potamilns alatus shells reflect variations in ambient water temperature and geochemistry of the Cannon River, so that the mollusk may serve as a high-resolution paleoclimate proxy.