Calcareous sediments spanning the last 13 ka fromn I,ake Zeribar, western Iran, were sampled for stable-isotope analysis as a means of augmenting earlier climatic interpretations based on polleni and macrofossils. The Lateglacial period was cold and dry, suLpporting semi-desert vegetation and highly concentrated lake water. Low evaporation rates due to the cold resulted in long residenice times and high lake stands. Durinig the earlv Holocene, the upland vegetation changed to a pistachio-oak savanna as low temperatures and ariditv J ameliorated. Lake level dropped in response to increased evapotranspiration. The low oxygen-isotope values of lacustiine calcite during this period are interpi-eted as a relative increase in the contributioni of winiter moisture rather than overall changes in effective moistuLre. A gradual increase in oak pollen at 7 ka BP signalled the inicrease in effective moisture to levels simiiilar to those of today. At the same tinme the 5`1O values increased.A reflecting a greater percentage of "0-enriched spring rains. Modern values and seasonal distribution of precipi-HOLOCENE tation were established by 6 ka BP. A short-lived return to winter-only precipitation occuiTed at 4.5 ka BP SPECIAL ISSUE and resulted in a temporary increase in anrdity. The covariance among 6'3C, carbonate deposition and 6S'O values suggests that lake productivity is linked to these seasonal climiiatic changes.
A sediment core 7.2 m long from Lake Mirabad, Iran, was examined for loss-on-ignition, mineralogy, oxygen-isotopic composition of authigenic calcite, and trace-element composition of ostracodes to complement earlier pollen and ostracode-assemblage studies. Pollen, ostracode-inferred lake level, and high Sr/Ca ratios indicate that the early Holocene (10000 to 6500 cal yr BP) was drier than the late Holocene. Low δ18O values during this interval are interpreted as resulting from winter-dominated precipitation, characteristic of a Mediterranean climate. Increasing δ18O values after 6500 cal yr BP signal a gradual increase in spring rains, which are present today. A severe 600-yr drought occurred at ca. 5500 cal yr BP, shortly after the transition from pistachio-almond to oak forest. During the late Holocene, two milder droughts occurred at about 1500 and 500 cal yr BP. Within the resolution of the record, no drought is evident during the collapse of the Akkadian empire (4200–3900 cal yr BP). Rather, a decrease in δ18O values to early-Holocene levels may indicate the return to a Mediterranean precipitation regime.
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