Kalugin, A. Darin, G. Tretyakov, D. Rogozin

1. Geochemical anomalies in carbonate lacustrine sediments as seasonal and centennial environmental proxy for continental climate conditions in South Siberia during the last 2450 yrs. • Kalugin, A. Darin, G. Tretyakov, D. Rogozin Sobolev Institute of Geology and Mineralogy of SB RAS, Novosibirsk

2. Researchobject Meromictic Shira Lake (N54o30’, E90o12’) is located in semi-arid zone of Southern Siberia. It is a brackish water (salinity ~20 g/l) basin 9,4x5,3 km. Continental climate provides average July t~18o and January~ -20oC with annual ice cover (NDJFMA). Water stratification at depth ca 10 m keeps for a long time, in spite of lake level oscillation up to 6 meters during historical observations.

3. Age – depth model Cal 14C age for 145 cm core Reservoir effect 1200 years Age for uppermost layers, counted: By visible annual layers and Ca/Sr signal Position of 137Cs peak for 1963 y. global fallout Intervals of low level are looked like white layers

4. Minerals and chemical composition of sediments corresponded to meromictic and holomictic periods Meromictic stage Holomictic stage white layer agrees to drop in the lake level

5. Evaluation of temperature oC using thermodynamic modeling of multisystem –general view. Aim of investigation - Estimation of behavior of the atmosphere – water – sediment - pore solution system with an equilibrium thermodynamic modeling The physico-chemical modeling is widely applied in geochemical research. Generally, it concerns to water-rock interaction in the “black smoker” or magmatic systems (Alt, Shanks, 2003; Palandri, Reed, 2004 et al.). However, there is a few information about physico-chemical modeling in respect with pore water-sediment system. So, this is a new estimation method for sediment-formation conditions in the lakes. 1) Source data – 1) rock-forming minerals in sediment, 2) chemical composition of dry sediment, 3) composition of pore water from the same sample of sediment, and 4) rock-water ratio 2) Instrument Software - “Selektor” (Karpov et al., 1997) for the Gibbs free energy minimization in multisystem, composed of main chemical elements: H, O, C, S, P, Si, Ti, Al, Fe, Mn, Ca, Mg, Na, K, Sr, etc., which occur in the chemical analysis of sediments. All known chemical molecules and ions, which have thermodynamic constants collected in the special databases, serve for computing 3) Results - Content of solid mineral phases, dissolved ions and gases, water and gas (mas. %) depending on outer factors: temperature, salinity, pH, solid-water-gas ratio, partial pressure of gases (O2, CO2, H2S...) and so on in condition of thermodynamic equilibrium in the source carbonate rock + pore water system

6. Calculation for mineral content (mol), precipitated from Shira lake water under various temperature in interactive water – atmosphere system Solubility of Carbonates

7. Minerals equilibrium in the conditions of salinity increase Model for intra-annual distribution of terrigenous (Rb),chemogenic (Sr) and biogenic (Br) elements averaged on 15 layers. Horisontal scale is proportional to thickness.

8. Rhythmic layerwise distribution of elements (normalized content, filtered by 3) on depth and time scale. Step of measurement 0.1 mm. Dash line divides warm season from below and cold one from above within annual rhythms. left side - terrigenous (Rb) and opposite biogenic (Br) profiles, right side - chemogenic carbonates (Ca, Sr) and X-ray density (XRD) conformal profiles.

9. Sr – anomaliesmark white intervals corresponding to low lake level and high water salinity Organics content as Core is analysed by SR XRF scanner, measurement step 0.1- 0.2 mm

10. Periodicity of high water salinity by a Br/Sr ratio Years AD

11. Brrepresents organic component of sediment СаandSr– carbonates K, Ti,Rb and Y – mineral component

12. Weather – climate variability reconstructed Holomictic periods are markedby light rectangles limited by Sr anomalies.They are repeated each ~500 yrs. Reconstruction equation was calculated by multiple regression trained on instrumental data from 1937 to 2007 y. Correlation between reconstructedand instrumental time series

13. Conclusions • Seasonal sedimentation in Shira lake results in two contrast laminas within annual rhythms: black one containing organic matter deposited in winter (November- April), and white, organic free – in summer (May – October). • 2. Sentennial periodicity of essential carbonate sedimentation looked like white intervals along the core and marked by Sr anomalies is revealed.That process was stipulated by drop in the lake level together with increase of water salinity • 3. So light carbonate Sr-enriched laminas are formed just after each cold season during meromictic (normal) state of lake. More thick light intervals corresponded to extremely low lake level periods of holomictic state are repeated every 450-550 yrs. • See publication: I.Kalugin, A. Darin, D. Rogozin, G. Tretyakov. Seasonal and centennial cycles of carbonate mineralisation during the past 2500 years from varved sediment in Lake Shira, South Siberia. Quaternary International 290-291 (2013) 245-252. DOI 10.1016/j.quaint.2012.09.016.