HR: 1330h
AN: PP23A-03    [Abstracts]
TI: The Oxygen, Hydrogen and Carbon Isotope Compositions of Modern Freshwater and Terrestrial Snails, Pinery Provincial Park, Southern Great Lakes Area, Canada
AU: * Heidenheim, J
EM: jaheiden@uwo.ca
AF: Department of Earth Sciences, The University of Western Ontario, London, ON N6A B57 Canada
AU: Longstaffe, F
EM: flongsta@uwo.ca
AF: Department of Earth Sciences, The University of Western Ontario, London, ON N6A B57 Canada
AB: We have compared the oxygen, hydrogen and carbon isotope compositions of several species of modern freshwater and terrestrial snails from a variety of ecosystems in Pinery Provincial Park, southwestern Ontario. The Park is located on the shore of Lake Huron, within a temperate-humid climatic regime. The aquatic snails have a range of oxygen and hydrogen isotope body-water compositions with a slope similar to the local evaporation line of their river and pond habitats. Body water from terrestrial snails has oxygen and hydrogen isotope compositions with a similar slope to the local soil-water line. Body-water compositions tend to be slightly enriched in oxygen-18 relative to the source water. The oxygen isotope composition of the shell aragonite most closely predicts body-water compositions for the average temperature of snail growth. Snail flesh is enriched in carbon-13 relative to diet by about 3 per mil. The aquatic shells are enriched in carbon-13 relative to flesh by an average of 11 to 20 per mil, depending on species. Shells of the two terrestrial species examined are enriched in carbon-13 relative to flesh by an average of 10 to 12 per mil. The diversity of snail microhabitats in the Park is reflected in the carbon and oxygen isotope compositions of their shells. Bottom-dwelling aquatic snails have relatively constant oxygen isotope values, which reflects limited variation in their source water composition. By comparison, shell carbon isotope values are highly variable, a consequence of compositional changes during the cycling of organic matter. Surface-dwelling aquatic snails and those living in very shallow water columns exhibit a range of positively correlated oxygen and carbon isotope values. This pattern reflects systematically changing water and carbon source compositions during the growing season. Terrestrial snail aragonite has a large range in oxygen isotope values, arising from the wide variation in composition of the slightly evaporated precipitation from which it is derived. In contrast, terrestrial shell carbon isotope values are constant, reflecting the uniform composition of the terrestrial organic carbon supply. The large range in shell oxygen and carbon isotope values obtained for this small area underscores the importance of microhabitat. The possibility of such variability needs to be considered when interpreting data for ancient snail shells formed in similar environments.
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2005 Joint Assembly