HOLOCENE TRENDS IN O-18 IN LAND SNAIL SHELLS FROM THE NEGEV DESERT AND THEIR IMPLICATIONS FOR CHANGES IN RAINFALL SOURCE AREAS

The δ18O value of the carbonate of land snail shells is related to the 18O content of precipitation, which in turn relates to the source region and trajectory of the rain-bearing air masses. Analyses of 18O of the shell carbonate of 76 radiocarbon-dated Holocene samples of the land snail Trochoidea seetzeni from the northern Negev Desert in southern Israel were carried out and the results were compared to modern snails from the same region. Early Holocene δ18O values are similar to modern but during the period centered around 6500-6000 yr B.P., a depletion of some 2%. below modern is observed. A change in the atmospheric circulation pattern for this period is thus indicated, most likely an increase in the frequency of storm systems reaching the region from north-eastern Africa. By 3500 yr B.P., δ18O values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time. © 1991.