NOAA/WDS Paleoclimatology - Soreq Cave, Israel Speleothem Oxygen Isotope Data 2.2-0.9 ky BP

Analysis of oxygen isotope ratios (d18O) 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 permil in d18Ocalcite values across our sample, the methods described here reveal up to 2.15 permil variation within single annual growth bands. Values of d18O 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 d18Ocalcite values record regular seasonal differences in d18Orainfall modified by mixing in the vadose zone. Large differences in d18O values measured across a single band (i.e., between the dark and light fluorescent calcite, or Delta18Odark-light) are interpreted to indicate wetter years, while smaller differences represent drier years. Oxygen isotopes record: 1) month-scale growth increments, 2) changes in Delta18Odark-light that represent seasonality, 3) a systematic, long-term decrease in maximum Delta18Odark-light values, and 4) an overall increase in average d18Ocalcite 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.