LATE GLACIAL-HOLOCENE ENVIRONMENTAL RECONSTRUCTION IN SOUTHERN IBERIA AS INFERRED FROM THE STABLE ISOTOPE COMPOSITION OF FRESHWATER GASTROPOD SHELLS

The freshwater gastropod Radix balthica is one of the most common continental molluscs in Europe found both in modern ecosystems and Quaternary records. The carbon and oxygen isotopic composition of the aragonitic shell of this genus has been successfully used to infer changes in Quaternary environmental conditions in Asia and northern Europe. This study analyzes the isotopic composition of modern and fossil Radix balthica shells retrieved from the well-dated Padul-15-05 sediment core in Sierra Nevada, Granada, Southern Spain (37°00’ N; 3°36’ W). The investigated record comprises the last ~15,000 years and represents the southernmost isotopic study of this aquatic snail taxon. The ¹⁸O-enriched late glacial shells suggest that conditions in the lake were significantly colder and lake water δ¹⁸O values were higher than at present. The dramatically higher δ¹³C values of ~15 ka old shells also suggest that the δ¹³C values of the dissolved inorganic carbon (DIC) in the lake was enriched in ¹³C during the late glacial interval. Significantly negative shell δ¹⁸O and δ¹³C values around 6.6 cal ka indicate that conditions were warmer, and that water δ¹⁸O and DIC δ¹³C values of the lake were notably lower during the middle Holocene compared to the late glacial. From middle to late Holocene, environmental conditions seem to have fluctuated but overall temperatures remained warmer, and water δ¹⁸O and DIC δ¹³C values were lower than during ~15 cal ka. Variations in gastropod abundance, temperature, and water δ¹⁸O and DIC δ¹³C values likely responded to changes in summer insolation intensity and/or evapotranspiration shifts from the late glacial to recent. This study reinforces the validity of aquatic gastropods as environmental proxies in southern Iberia, which can complement and expand other more commonly used lake proxies.