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 δ 18 O(CaCO3) and δ 13 C(CaCO3) values for sub-weekly climate records. Seasonal variation in δ 18 O(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 δ 18 O(CaCO3) values predicted by Patterson et al. (1993), while Dreissena polymorpha produces δ 18 O(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.