Sedimentary lipid biomarkers in the magnesium rich and highly alkaline Lake Salda (south-western Anatolia)

Abstract

Lake Salda, located in south-western Anatolia, is characterized by the presence of living stromatolites and by a low diversity of both phytoplankton and zooplankton due to high pH and magnesium concentration. The most abundant, free sedimentary lipids of the uppermost five centimetres of the lake sediments were studied as potential environmental biomarkers, and proxies based on glycerol dialkyl glycerol tetraethers (GDGT) were tested in this extreme environment. Dinosterol and tetrahymanol are potentially relevant biomarkers for the dinoflagellate Peridinium cinctum and ciliates, respectively. C-20: 1 and C-25: 2 highly branched isoprenoid (HBI) alkenes, and n-C-17 alkane and n-C-17: 1 alkene are considered to represent, respectively, diatoms and Cyanobacteria, that are involved in the formation of stromatolites. Crenarchaeol is assumed to be derived mainly from Thaumarchaeota thriving in the lake. Allochthonous organic material is represented by long-chain n-alkanes and n-alkanols derived from land plant leaf waxes, as well as branched GDGTs produced by soil bacteria. The latter may also be produced partly in the water column and/or the surface sediment of the lake. Branched GDGT-derived lake calibrations for water pH provide estimates close to observations, but estimated lake water/air temperature are lower than observed values. TEX86 (tetraether index of tetraethers consisting of 86 carbons), a proxy based on isoprenoid GDGTs, potentially allows estimating mean annual lake surface temperature. Interestingly, C-22 to C-25 1,2 diols, which have a yet unknown origin, were found for the first time in lake sediments. This study represents the first investigation of sedimentary lipid distribution in an alkaline and magnesium-rich lake in Anatolia, and provides a basis for future biomarker-based paleoenvironmental reconstruction of Lake Salda.