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 δ13Cshell 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 δ18Oshell 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.