Climate deterioration in the Eastern Mediterranean as revealed by ion microprobe analysis of a speleothem that grew from 2.2 to 0.9 ka in Soreq Cave, Israel

Analysis of oxygen isotope ratios (delta O-18) by ion microprobe resolves a sub-annual climate record for the Eastern Mediterranean from a Soreq Cave stalagmite that grew between 2.2 and 0.9 ka. In contrast to conventional drill-sampling methods that yield a total variation of 1.0 parts per thousand in delta O-18(calcite) values across our sample, the methods described here reveal up to 2.15 parts per thousand variation within single annual growth hands. Values of delta O-18 measured by ion microprobe vary in a regular saw-tooth pattern that correlates with annual, fluorescent growth banding where calcite grades from light to dark fluorescence. Modern records of precipitation and of cave dripwater indicate that variable delta O-18(calcite) values record regular seasonal differences in delta O-18(rainfall) modified by mixing in the vadose zone. Large differences in delta O-18 values measured across a single band (i.e., between the dark and light fluorescent calcite, or Delta O-18(dark-light)) are interpreted to indicate wetter years, while smaller differences represent drier years. Oxygen isotopes record: 1) month-scale growth increments, 2) changes in Delta O-18(dark-light) that represent seasonality, 3) a systematic, long-term decrease in maximum Delta O-18(dark-light) Values, and 4) in over-all increase in average delta O-18(calcite) values through time. These results Suggest a drying of regional climate that coincides with the decline of the Roman and Byzantine Empires in the Levant region. (C) 2008 University of Washington. All rights reserved.