Oxygen isotope signatures from land snail (Helix melanostoma) shells and body fluid: Proxies for reconstructing Mediterranean and North African rainfall

- Live H. melanostoma land snails were collected from a transect in the Gebel Akhdar.
- Snail body fluid oxygen isotopes reflect local precipitation composition.
- Snail shell oxygen isotopes are highly correlated with precipitation amount and rainfall oxygen isotope composition.
- We developed equations to reconstruct rainfall composition and precipitation amount from shell oxygen isotopes.
- These equations can reconstruct palaeorainfall parameters from archaeological and geological H. melanostoma shells.

In this paper, we show that oxygen isotope ratios from the shell carbonate of the land snail Helix melanostoma reflect local rainfall parameters. Stable oxygen isotopes were measured in the body fluid (δ18Obody) and shells (δ18Oshell) of live-collected H. melanostoma along a north-south transect across the Gebel Akhdar in northeast Libya. δ18Obody ranged between − 8.1‰ and 13.0‰ whilst δ18Oshell ranged between − 1.0‰ and + 2.8‰. To investigate the relationship between snail oxygen isotope composition and climate, these measurements were correlated with ambient air temperature, relative humidity, rainfall amount, and the δ18O composition of rainwater (δ18Orain). Strong and significant correlations were found between δ18Oshell and δ18Orain, and between δ18Oshell and rainfall amount (R2 = 0.79 and 0.85 respectively) suggesting that H. melanostoma shells can be used as a proxy for past rainfall conditions. When combined in multiple linear regressions, δ18Orain and rainfall amount explained 90% of the variance in δ18Oshell (R2 = 0.90). Simple and multiple linear regressions were used to develop predictive models for these climate parameters. As H. melanostoma shells are commonly found in Mediterranean and North African archaeological and geological deposits, the predictive equations developed in this study hold great potential for reconstructing Pleistocene to Holocene rainfall and aridity patterns in the Gebel Akhdar and for assessing the relationship between environmental changes and human behavioural changes.