Seasonal variation in stable oxygen and carbon isotope values recovered from modern lacustrine freshwater mollusks: paleoclimatological implications for sub-weekly temperature records

Abstract

A fingernail clam (Sphaerium simile, Sphaeriidae) from Science Lake, a small watershed located in Allegany State Park, New York, USA and a zebra mussel (Dreissena polymorpha, Dreissenidae) from Keuka Lake, New York, the third largest Finger Lake of central New York, were selected to evaluate the applicability of using δ18O(CaCO3) and δ13O(CaCO3) values for sub-weekly climate records. Seasonal variation in δ18O(CaCO3) values was compared with predicted equilibrium values to test the hypothesis that lacustrine molluscs produce shell aragonite according to environmental variables. For the purpose of comparison, aragonite temperature-fractionation equations determined by Grossman & Ku (1986) and Patterson et al. (1993) were used. Sphaerium simile appears to produce δ18O(CaCO3) values predicted by Patterson et al. (1993), while Dreissena polymorpha produces δ18O(CaCO3) values in agreement with Grossman & Ku (1986). We attribute the difference to family-specific temperature-fractionation relationships. Because both types of mollusc record climate variables with a high degree of integrity, they should each serve as excellent paleoclimate proxies.

The fingernail clam collected from a small watershed exhibits higher variation about the seasonal pattern than did the zebra mussel collected from a large watershed. This is attributed to the increased sensitivity of the small watershed to storm perturbation. Analysis of fossil molluscs from such watersheds might be useful in discerning paleo-storminess.