Impacts of environmental deterioration on the carbon isotope values of modern vegetation and gazelles in the southern Levant: Predicting the severity of the Younger Dryas

摘要

This study uses the carbon isotope values (δ ~(13)C) to determine how environmental deterioration is expressed in the δ ~(13)C values of vegetation and gazelles in the southern Levant. The ultimate goal is to use these modern data to predict the climatic impact of the Younger Dryas (YD). Climatic deterioration associated with the YD has been cited as the trigger for the transition to agriculture in the southern Levant. However, the evidence for the local severity of this climatic event is equivocal. There is disagreement over whether Mediterranean forest was succeeded by arid adapted steppic plant communities in what has been termed the Natufian 'core area'. The modern data show a moderately negative regression slope between aridity and the δ ~(13)C values of both modern C _3 plants and gazelle horn keratin within the Mediterranean phytogeographic belt. This pattern is expressed in both seasonal and annual datasets. The incorporation of a C _4 plant component into gazelle diets is evident in the arid Mediterranean region, and is more pronounced in the dry season. The latter is apparent even despite interference caused by gazelle foraging on cultivated land. Based on the present day data, it is predicted that the succession of Mediterranean forest by open steppic vegetation would cause a positive shift of ≤2% in the δ ~(13)C values of C _3 plants and gazelles. The argument is based on the response of C _3 vegetation to growth under increasing water stress conditions and the current distribution of C _3 and C _4 vegetation in relation to rainfall. This study presents a new tool with the potential to assess the climatic severity of the YD and its effect on Natufian foraging strategies.