High resolution stable isotope ratios in modern African land snails: Testing inferred environmental conditions

International audience High-resolution sub-annual stable oxygen isotope data were measured in modern land snail shells collected fromdifferent climatic zones in Africa to search for patterns in seasonal δ18O cycles associated with specific hydro-climates, keyed to flora/biozones. Thirty-three recently dead shells were collected between 1995 and 2012, andcollection localities were divided into five climate types: tropical forest, woodland savannah, bushland savannah,woodland monsoon, and arid/semi-arid. Thirteen genera are represented in the collection. Sampling covered atleast one year in the life of the land snails, often multiple years. A comparison of measured data to predicted δ18Ovalues, using local temperature and rain δ18O value, shows that predictions tend to be lower than measuredvalues, suggesting that surface waters or snail body waters have undergone some evaporation. Predictions basedon night-time temperatures (average monthly minimum T) are closer to, but still underestimate, measured valuescompared to day-time (maximum) temperatures in a majority of cases. The largest range in δ18O values forindividual shells occurs in the bushland savannah and woodland monsoon biomes. Longer seasonal intervals ofdry conditions lead to greater δ18O ranges in shells, although if the dry interval approaches 10 months in the yearthe amplitude is again reduced. This is in agreement with other oxygen isotope studies of high-resolution landsnail shell samples, which show very high δ18O variance in strong monsoon climates.