Evironmental change in southwestern Iran: the Holocene ostracod fauna of Lake Mirabad

Abstract

Ostracod faunal data are presented from a sediment core taken from extant Iranian Lake Mirabad. Ostracod faunal successions indicate relatively high concentrations of mainly nektonic taxa between c. 9265 and 6505 cal. 14C yr BP, followed by lower concentrations of mainly benthic forms after 6505 cal.BP. These results suggest that lake levels were low during the early Holocene, and that water levels rose during mid- Holocene times, notably after c. 4048 cal. 14C yr BP. These findings confirm and consolidate palaeoclimatic inferences based on previously published pollen diagrams from the region, but indicate an apparent timelag between the early to mid-Holocene forest advance and increased lake levels. This may be explained by changes in precipitation/evaporation ratios; the increase in winter precipitation was sufficient to allow the expansion of arboreal vegetation, but summer evaporation remained high. This also gives support to the idea that the delayed readvance of forests in eastern Turkey and western Iran in the early Holocene was hampered by dry conditions in the continental interior. The apparently out-of-phase response observed between the palaeoclimate record from Lake Mirabad and from other sites in northern Africa, the eastern Mediterranean and Arabia may be explained by shifting atmospheric circulation patterns and varying amplitudes of precipitation as a consequence of changes in insolation. To promote further ostracod palaeoecological research in the Near East, a checklist of non-marine Ostracoda known from modern Iran is presented as an appendix.