Climate and environmental changes during the past 1,500 years in Altai, Western Siberia, Russia: elemental geochemistry from four lake cores

Gravity cores of four lakes along a NE to SW transect in Altai Mountains, from Shira Lake to Manzherok Lake, to Beloye Lake and Kolyvanskoye Lake, have been precisely dated by 210Pb, 137Cs and AMS 14C methods. High-resolution measurements of TOC and TON by EA, and 0.5N HCl leaching (AL) and Aqua Regia dissolved (AR) elemental concentrations by ICPOES reveal lake productivity, salinity, pH, redox condition and surface runoff under climate change and human impact over the past 1500 years. All of the lake sediments contain high sedimentary organic matter (average TOC >5%). However, 14C dating on the TOC as well as aquatic plants show old carbon influence (OCI). In order to obtain correct chronology of the cores, it is necessary to make high-resolution 14C dating. Using the least OCI 14C ages and combing 210Pb/137Cs dating results, a reliable chronology of the sediment core can be established. The AL fraction reflects mainly changes in lake chemistry, whereas the AR fraction represents chiefly variations in terrigenous input. The AL Ca and Sr are indicators of lake salinity, alkalinity and pH, whereas the AL Mo, Fe and Al are indicators of redox condition of the lake. TOC% and C/N are proxies for lake productivity and exogenous/endogenous TOC ratio. The AL Zn and Pb concentrations shows human impact. Based on the four lake records, the climatic conditions during the past 1500 years can be identified: warm and wet during 1500~1100 cal yr BP; warm and wet during 1100~900 cal yr BP (Medieval Warm Period -- MWP); fast sedimentation rate due to strong surface runoff during 900~700 cal yr BP; cooling and drying climates during 700~500 cal yr BP; very slow sedimentation due to longer frozen surface under cold climates during 500~50 cal yr BP (Little Ice Age -- LIA).  Since AD1900, the lakes were started to resume lake productivity under warming climate with the smaller lake first, being Manzherok (0.4 km2) in AD1900, Beloye (2.97 km2) in AD1920, Kolyvanskoye (4.5 km2) in AD1940, and Shira (39 km2) in AD1950. This study is supported by the Russian Science Foundation (RSF) (grant No.22-47-08001) to Kazan Federal University (KFU).