Late Quaternary paleoclimate and paleoenvironment changes in Lake Urmia, NW Iran

Lake Urmia, a hypersaline lake in NW Iran, is situated in a tectonically active and climatically sensitive region. It has been gradually desiccating, endangering its unique biodiversity, including an endemic brine shrimp, Artemia urmiana. The present study documents multiproxy analyses of a 25 m-long sediment core recovered from the northern part of Lake Urmia. Lake sediment multiproxy data provide the basis for extensive documentation of lake history, climatic changes, as well as sedimentation processes. The timing of variable climatic conditions in the lake is determined by the age-depth model of the core based on radiocarbon dating. Four well-dated radiocarbon ages obtained from pollen samples suggest a late Quaternary sequence. However, generating a reliable and continuous age-depth model requires additional age data. Visual lithological observations and physical properties of the sediments document high lithofacies variations throughout the core. The sedimentary sequence is composed of biochemical and terrigenous mud and sand, micrite and clay minerals, sulfate and chloride minerals, and fecal pellets of Artemia and coated grains. The core sediments were subdivided into six sedimentary units. The lowermost part consists of dark grey-coated grains. The overlying unit consists of silty clay that varies from brown to greenish-grey and alternates with fecal pellets and coated grains. The subsequent unit is composed of brown clay minerals and fecal pellets. The upper boundary of the next unit, consisting of alternations of sulfate minerals (mostly gypsum) and fecal pellets, is marked by a color change from brown to greenish-grey. The uppermost-examined sediments are richer in pellet content; towards the top, pellets are fewer and are in a carbonate matrix. A salt crust (up to 3 m) from a recent drying event constitutes the surface sediments. These findings are combined with high-resolution µ-XRF and TOC analyses to infer a complete picture of paleoenvironmental variations on the lake. Hypersaline lakes are extreme habitats, mostly with very low productivity. However, high TOC content in some parts of the core can be attributed to organic matter production. The high-resolution smear-slide observations indicate that high TOC content mainly corresponds to rich fecal pellet layers. Intense fluctuations in the elemental profiles imply high variations in paleoclimate. The Ca-Ti ratio correlates positively with TOC content, indicating endogenic carbonate production due to the warm and dry climate. The general low µ-XRF Fe-Mn ratio throughout the core strongly suggests that the deep-water column in the lake could never have been anoxic but mostly suboxic to oxic due to high water circulation as a consequence of low lake level. The warm and wet climate period can be documented in µ-XRF K, Fe, and Ti profiles, partly supported by high MS values. Lower Ca-Sr ratios in the µ-XRF mainly correspond to sulfate minerals, primarily gypsum. We also carried out high-resolution pollen studies that brought further insights into the reconstruction of paleovegetation and paleoclimate changes. This work is supported by the TUBITAK 118C329 and ITU BAP 42972 projects.