Paleoclimate of the Last 50,000 Years In the Canary Islands Inferred from the Stable Isotope Composition of Land Snail Shells

Tropical-subtropical climate in western Africa has oscillated from wetter to drier conditions in response to global interactions between orbital forcing, atmosphere, ocean and land surface conditions. In the eastern Canary Islands, a low latitude oceanic setting, there is a large fossil record of land snail shells preserved in eolianite deposits that expand back in time ~50,000 years. In this study, we analyzed the δ¹⁸O and δ¹³C values of 145 shells to rebuild the Late Pleistocene-Holocene climate of the Canary Islands.

The δ¹³C values of shells ranged from -9.6‰ to +2.5‰ (V-PDB). These values record the vegetation that snails consumed (C₃/C₄ plants), which depends on the available plants in the landscape. More negative δ¹³C values indicate a greater percentage of C₃ in the diet, while more positive values suggest a diet primarily based on C₄ plants, which has been interpreted as wetter and drier conditions, respectively. Based on these inferences, lower δ¹³C_shell values at ~30 and 11 kyr suggest wetter conditions than the present.

The δ¹⁸O values of shells varied between -1.9‰ and +3.2‰ (V-PDB). The δ¹⁸O_shell results are related to the isotope composition of the ambient meteoric water and the temperature at which the shells were grow. Shells dated at ~30, ~15 and ~11 kyr displayed more negative δ¹⁸O values, which is indicative of colder/wetter times based on the relationship between air temperature and the δ¹⁸O value of meteoric water (or amount effect). Similarly, shells from the Last Glacial Maximum (18-23 kyr) displayed lower average δ¹⁸O values than modern snails, indicating cooler temperatures than today.

These results corroborate previous climatic proxies from tropical-subtropical Africa, confirming the reliability of the stable isotopes of land snail shells as paleoclimatic indicators. Consequently, well-preserved shells from low-latitude and oceanic islands are useful to rebuild local climate shifts through time.