OXYGEN STABLE ISOTOPES OF LAND SNAIL SHELLS: PALEOENVIRONMENTAL IMPLICATIONS FOR LOW-LATITUDE OCEANIC SETTINGS

Land snails provide a unique opportunity to study terrestrial paleoenvironments because their shells, which are well preserved in the fossil record, contain a temporal record of environmental change in the form of isotopic codes. To evaluate the utility of this approach for low latitude oceanic settings, 207 modern shells of 18 species of land snail were analyzed for their oxygen isotope composition along an altitudinal gradient (from 10 to 2,160 m a.s.l.) in Tenerife Island of the Canary Archipelago. The d¹⁸O values of shell material ranged from -2.9 to +3.9‰ (VPDB) and displayed a negative correlation with elevation, which is consistent with the positive relationship observed between temperature and the d¹⁸O value of meteoric precipitation. Calculated d¹⁸O values for water derived from observed temperatures and d¹⁸O values of shell material (using the equation of Grossman and Ku, 1986) were similar from measured d¹⁸O values for local rain water. The calculated values declined 0.1699‰ (VSMOW) per 100 m, which is consistent with the "altitude effect" observed for tropical rains in Western Africa. These results suggest the oxygen isotope composition of land snail shells are a meaningful proxy for temperature and precipitation, where more negative d¹⁸O values for shell reflect lower d¹⁸O values for rain water and lower temperatures (in contrast to marine shells), which are indicative of wetter and/or cooler conditions. Finally, no significant difference was observed between the average d¹⁸O value for any species, suggesting that multi-taxa data sets may be used to infer environmental conditions when collecting individuals of a single species is unfeasible.