Oxygen and Carbon Isotope Compositions of Land Snail Shells from ~8ka B.P. Archeological Sites in Interior Algeria

Well-preserved aragonitic shells from Early Holocene land snail species ranging in age from ~7300 to 9600 (¹⁴C years) were collected from the archeological sites Aïn Misteheyia (AM) and Kef Zoura D (KZD) in northeastern Algeria in the 1970s. Measured d¹⁸O values of Helix melanostoma shells ranged from -3.3‰ to 0.0‰ (PDB) at AM and -3.1‰ to -0.6‰ at KZD. At AM, the d¹⁸O values of Hygromiidae sp. shells ranged from -2.0‰ to 0.7‰ and, at intervals of abrupt, persistent change in d¹⁸O, exhibited an approximately antithetical relationship with the d¹⁸O variation of Helix. d¹³C values ranged from -9.9‰ to -5.8‰ (PDB) and from -10.8‰ to -8.7‰ for Helix at AM and KZD, respectively. Similar values were obtained for Hygromiidae at AM (-9.1‰ to -6.6‰). The d¹³C data indicate a diet of predominantly C3 organic matter for both snail species. The average d¹⁸O values (-5.0‰) of winter precipitation from an Algerian IAEA site were combined with a published oxygen isotope flux balance model to calculate expected values of snail shell d¹⁸O as a function of relative humidity and temperature. Comparison of model-predicted shell d¹⁸O values with measured values for both species suggests that the ranges in the measured values of d¹⁸O could reflect fluctuations in winter relative humidity of as much as 10%. The possible effect of relative humidity on the observed d¹⁸O values of snail shells suggests that microenvironmental, seasonal and/or physiological factors may have played a role during the times in which the d¹⁸O of Helix and Hygromiidae vary antithetically at the AM site. One of these times may temporally correspond to an abrupt decrease in d¹⁸O observed ~8.2ka B.P. in the Greenland ice cores. d¹⁸O indications of a North African ~8ka climatic perturbation may have implications for the development of human cultures in the area.