干旱区生态环境知识资源中心

Calcareous sediments spanning the last 13 ka from Lake Zeribar, western Iran, were sampled for stable-isotope analysis as a means of augmenting earlier climatic interpretations based on pollen and macrofossils. The Lateglacial. period was cold and dry, supporting semi-desert vegetation and highly concentrated lake water. Low evaporation rates due to the cold resulted in long residence times and high lake stands. During the early Holocene, the upland vegetation changed to a pistachio-oak savanna as low temperatures and aridity ameliorated. Lake level dropped in response to increased evapotranspiration. The low oxy.-en-isotope values of lacustrine calcite during this period are interpreted as a relative increase in the contribution of winter moisture rather than overall changes in effective moisture. A gradual increase in oak pollen at similar to7 ka BP signalled the increase in effective moisture to levels similar to those of today. At the same time the delta O-18 values increased, reflecting a greater percentage of O-18-enriched spring rains. Modem values and seasonal distribution of precipitation were established by 6 ka BP. A short-lived return to winter-only precipitation occurred at similar to4.5 ka BP and resulted in a temporary increase in aridity. The covariance among delta C-13, carbonate deposition and delta O-18 values suggests that lake productivity is linked to these seasonal climatic changes.