Carbon isotope signatures from land snail shells: Implications for palaeovegetation reconstruction in the eastern Mediterranean

摘要

In this study we compare carbon isotope values in modern Helix melanostoma shell carbonate (delta C-13(shell)) from the Gebel al-Akhdar region of Libya with carbon isotope values in H. melanostomabody tissue (delta C-13(body)), local vegetation (delta C-13(plant)) and soil (delta C-13(soil)). All vegetation in the study area followed the C-3 photosynthetic pathway. However, the delta C-13(plant) values of different species formed two distinct isotopic groups. This can be best explained by different water use efficiencies with arid adapted species having significantly more positive delta C-13(plant) values than less water efficient species. The ranges and means of delta C-13(body) and delta C-13(plant) were statistically indistinguishable from one another suggesting that delta C-13(body) was primarily a function of local vegetation composition. H. melanostoma delta C-13(shell) reflected the delta C-13(plant) of local vegetation with a positive offset between body/diet and shell of 14.5 +/- 1.4 parts per thousand. Therefore, in the Gebel al-Akhdar where only C-3 plants are present, highermeand delta C-13(shell) values likely reflect greater abundances of water-efficient C-3 plants in the snails diet and therefore in the landscape, whilst lower mean delta C-13(shell) values likely reflect the consumption of less water-efficient C-3 plants. The distribution of these plants is in turn affected by environmental factors such as rainfall. These findings can be applied to archaeological and geological shell deposits to reconstruct late Pleistocene to Holocene vegetation change in the southeast Mediterranean. (C) 2015 Elsevier Ltd and INQUA. All rights reserved..