Reconstruction of annual air temperatures for three thousand years in Altai region by lithological and geochemical indicators in Teletskoe Lake sediments

Limnological studies show that the variation of climate conditions over the catchment area of the lake are reflected in the composition and structure of bottom sediments, allowing one to use the measurable physicochemical characteristics of the sediments for the reconstruction of paleoclimate conditions. The mountain lakes of Siberia were not subjected to any significant anthropogenic pollution over the last 100‐150 years, which is the period of instrumental measurements. Thus, the geochemical composition of the upper layers of the sediments may be correctly calibrated by present-day weather data. Teletskoe Lake is a suitable object for these studies because here, in recent years, a continuous sequence of bottom sediments was studied, the steady correlation of the sediment composition and properties to the weather survey data was established, the procedures of high-resolution analyses were elaborated, and the annual climate variations were reconstructed for the last 800 years [1, 2]. Bottom sediments in Teletskoe Lake are constituted by carbonate-free terrigenous silty clays of low content of allochthonous organic detritus (1.14% of the total carbon) and of biogenic silica (2.5%). The sediment formation represents the weather conditions well because the matter supply to the basin coincides in mass to its deposition for a year [2]. The column of bottom sediments 190 cm length was taken out in 2006 with a gravity tube from the isolated underwater Ridge of Sofia Lepneva, which reaches from the bottom of 200‐250 m depth to a depth of 90 m at the site of the 51°44.99 ′ N, 87°37.414 ′ E coordinates. In the same place, using a box corer, a block of undisturbed sediments 14 × 14 × 20 cm in dimensions was taken. The block upper layers were used to create the age model. As the input data for the reconstruction, we used the time series of lithological and geochemical parameters and annual temperatures for AD 1840‐1996 from the Barnaul weather station. The measurement points were converted into the time scale on the basis of the estimates of the sediment accumulation rate by isotope dating: the peak of the 137 Cs content related to 1963; the logarithmic distribution of 210 Pb to the depth of 48 mm; and the radiocarbon age of the reference layer was 1105. To calculate the mass (dry) rate, the correction for water content was applied using the values of X-ray density calibrated by the water of content. The obtained value of the average linear rate of dry matter accumulation equal to 0.30 mm per year was used to create the time scale. The composition and physical properties of the sediments were studied by common procedures with discrete sub-sampling of 0.5 cm, and the continuous sequences were analyzed at the Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences, by means of X-ray fluorescence using the synchrotron radiation. With the equipment and procedures from [1, 3], blocks of dimensions 170 × 15 × 7 mm were scanned in steps of 100 µ m. The concentrations of over 20 elements characterized by the terrigenous and organogenous components of the sediment were deter