The impact of late Holocene environmental change on lacustrine Ostracoda in Armenia

Lake Sevan, Armenia, is an ancient lake, although it evolved into its present form only in the Holocene. The ostracod population was dominated by extant, spatially widespread species that have been recorded throughout Europe and Asia (e.g. Limnocythere inopinata, Ilyocypris bradyi, Cyprideis torosa, Candona candida and Candona neglecta), although a small proportion of the association is restricted to the Caucasus (e.g. Fabaeformiscandona caucasica). Diversity appears to reflect the gradual increase in water depths and environmental heterogeneity during the Sub-boreal European climatic phase (late in the Khvalynian climatic phase of the Caspian region). The muds, silts and sands penetrated by the boreholes contain shallow water ostracods indicating water depths of about 5 to 20 m. None of the boreholes penetrated deeper water deposits, so that Fabaeformiscandona dorsobiconcava, which lives at depths below c.40 m in the modern lake, was not found. Salinity was no greater than oligohaline; and water temperatures appear to have been cool. As is the case today, there were a number of streams transporting ostracods (such as Prionocypris zenkeri and Ilyocypris bradyi) into the lake and weeds were abundant. The Holocene association of Lake Sevan is unusual in that it is one of the few in which bisexual populations of Limnocythere inopinata occur.