Seasonal and centennial cycles of carbonate mineralisation during the past 2500 years from varved sediment in Lake Shira, South Siberia

Shira Lake is a good representative object for detail weather-climate modeling due to its local hydroclimatic information and annually laminated bottom sediments. Carbonate biochemical mineralization in Shira Lake shows not only seasonal but also centennial pulses over each 450-500 years. An age-depth model has been built by layer counting combined with 137Cs and 14C isotopic dates. Thermodynamic estimation of the rock-water multisystem in conformity with local conditions and source matter provides grounds for interpretation of measured geochemical parameters in sediments including environmental indicators such as temperature, salinity, and pH. Scanning X-ray fluorescence for sub-millimeter microstratigraphic study of varves connects geochemical oscillations of microelement content (Rb, Ti, Ca, Sr, Br, XRD) with seasonality, as well as revealing centennial pulses of environmental change. Quantitative environmental reconstruction using multiple regression for precipitation calibrated by hydrometeorological time series year by year was carried out for the lake over the last 2500 years.