Interpreting stable isotope records from freshwater snail shell carbonate: a Holocene case study from Lake Golhisar, Turkey

The oxygen and carbon stable-isotope ratios from fossil snail shells within a small intramontane lake in southwest Turkey are used to highlight the potential, and problems, of using freshwater snail carbonate as a palaeoenvironmental proxy. Two species (Gyraulus piscinarum and Valvata cristata) yielded different isotope ratios at the same sampling intervals, probably due to differences in water-isotope composition between different microhabitats. Isotope ratios from a number of individual shells from the same sampling intervals (representing similar to7-25 years), show large ranges (up to 8parts per thousand for delta(18)O) for each species. Only by analysis of a significant number of species-specific shells (>5) from each sampling interval can a true understanding of environmental change be obtained. Averages of the data provide an insight into longer-term climatic variation while the ranges provide an estimate of short-term (decadal) environmental variability.