Reconstruction of Turgoyak lake (the Southern Urals) ecosystem changes in holocene

Abstract

Object. Multi-proxy analysis of 265 cm long sediments core of Lake Turgoyak, one of the deepest lakes of the Southern Urals, is presented. Materials and methods. The lake ecosystem changes was reconstructed based on diatom, radiocarbon dating and geochemical analysis. Statistical treatment of the surface sediments composition and hydrochemistry data of 56 lakes from Southern and Middle Urals lakes database allowed to obtain geochemical indexes for reconstruction of water parameters: index of organic matter content (ОМ = LOI550ºС/(Al2O3 + TiO2 + Na2O + K2O)) and index of salinity (ММ = LOI950ºC/LOI550ºС). Results. Radiocarbon dating shows that sedimentation in Lake Turgoyak was began more than 12 cal kyr BP ago. Each of six lithological units of sediments core is characterized by its own geochemical features and associated with global (11.8, 11.2, 8.2 cal kyr BP) and regional (12, 10.3 cal kyr BP) climate events of the Northern Hemisphere. Four main stages of Lake ecosystem development were identified: 1) the beginning of lake sedimentation (>12.1 cal kyr BP); 2) the stage of a subsaline shallow-water lake (12.1–11.2 cal kyr BP); 3) the stage of a freshwater lake with increased water-level (11.2–8.0 cal kyr BP); 4) the stage of water organic matter increase (<8.0 cal kyr BP). Conclusions. High content of mesohalobic diatoms and salinity module values showed significant increase of lake water salinity as response to Early Holocene climate warming (11.8–11.2 cal kyr BP). Pantle-Buck’s Saprobity Index and OM values pointed to the lake water organic matter increase due to the next climate warming since 9–8 cal kyr BP. Thus, Lake Turgoyak water parameters were reapeatedly changed during the Holocene. However the response of lake ecosystem was different in different periods of its development.