STABLE ISOTOPE CHEMISTRY OF BIOGENIC
CARBONATE AND LAKE WATER; CENTRAL
NEW YORK STATE
OLSON, Caroline, Department of Geology, Colgate University, 13 Oak Drive,
Hamilton, NY 13346, colson@mail.colgate.edu and SELLECK, Bruce,
Department of Geology, Colgate Univ, 13 Oak Drive, Hamilton, NY 13346
A study of water and mollusc (clam and snail) shell stable isotopes in Woodman
Pond has been undertaken to develop a baseline for continued annual sampling to
assess ongoing trends. Woodman Pond is a 92-acre hardwater kettle lake located
near the geographic center of New York State on the northern Appalachian
uplands. The lake has well developed marl benches and an abundant and diverse
gastropod fauna. Isotopic analyses of surface waters show evaporative
enrichment in the summer of 1999 (a relatively hot, dry summer) by up to 6 o/oo
in d18O. Gastropod shell carbonate precipitated that summer averages –7.9 o/oo
d18OPDB. In contrast, samples from the summer of 2000 (cool, wet summer)are
characterized by water and gastropod carbonate that are, on average, lighter in
terms of 18O by nearly 2.5 o/oo. Data from unionid bivalves are similar, but
annual differences are subdued, perhaps because of the benthic habit of the
clams. Carbon isotope data from bivalves suggest changes in either water depth
or dietary preferences as the clams grow. The results of this study suggest that
stable isotope data from gastropods may be a more sensitive indicator of climate
change in lake systems than bivalve data.