GEOGRAPHIC VARIATION IN δ18O OF LAND-SNAIL SHELLS IN EUROPEAN LOESS DURING THE LAST GLACIAL MAXIMUM

Land-snail shells have the potential to be a useful paleoclimate proxy for providing insight into the source region and trajectory of precipitation. Fossil gastropods (Arianta, Clausilia, Pupilla, Succinea, and Trichia) were gathered from Last Glacial Maximum (LGM) loess from Belgium east to the Czech Republic and southeast to Serbia. Modern samples (Bradybaena, Cepea, Helicondonta, Helicopsis, Helix, Trichia, and Zebrina) were collected from the surface near many of these sites and provide a control for comparison with fossil δ¹⁸O shell carbonate ratios. Both modern and fossil land-snail shells record δ¹⁸O values between 0‰ and -5‰. Within-shell and within-genus variability is similar to between-shell variability regardless of genus within sites. This supports earlier work that suggested there were no significant differences in shell δ¹⁸O between genera at a single location (Lécolle, 1985). Significant changes in mean shell δ¹⁸O do occur between sites. Therefore, we group δ¹⁸O values from different genera together to map the spatial distribution of δ¹⁸O in shell carbonate.

Oxygen-isotopic composition of gastropod shells reflects the spatial variation in the isotopic composition of precipitation. Modern land-snail shell δ¹⁸O decreases in Europe along a N-S gradient, where the highest mean δ¹⁸O values border the North Sea and decrease toward the Alps. Modern observed data of isotopes in precipitation (GNIP) demonstrate a similar trend for low-altitude sites. Much or most of modern Central European precipitation comes from the north or northwest and becomes more isotopically depleted inland toward the Alps, which block precipitation from the Mediterranean. LGM shell δ¹⁸O data show a different gradient with δ¹⁸O declining towards the ENE, implying a more southerly tropical to mid-Atlantic source. Balkan LGM samples show the influence of a Mediterranean source, with δ¹⁸O values decreasing northward toward Poland. This more southerly source of European precipitation agrees with the concept of a southward displacement of the North Atlantic Drift during the LGM.