Geochemical processes in Yamal peninsula lakes under climate variation

Climate change determines processes in Arctic lakes. Over the past ten years, within the framework of various projects, different types of Yamal lakes have been studied: deep glacio-karst Neytinskiye lakes in the central part of the peninsula and shallow thermokarst lakes formed due to melting of buried ice in the Yarkuta river valley; more than 50 lakes have been studied in total.  

The studied lakes differed markedly in transparency (2-7 м), water bottom temperature (6-18°C), electrical conductivity (97-465 μS/cm), turbidity (6.73-34.3 FTU), chromaticity (9.8-46.7°), dissolved oxygen (5-10 mg/l), depending on their location, depth, the influence of melting buried ice, and local conditions. The concentration of biogenic elements (NO3, NO2, PO4, and SiO2) was insignificant, reaching a maximum of 2.63 mg/L, 0.07 mg/L, 1.05 mg/L, and 3.82 mg/L, correspondingly. pH values ​varied within a small range - 6.1-7.68, showing the neutral lakes environment.

For Yamal lakes, the values​ of stable oxygen isotopes δ18O corresponded to the lateral inflow of water into the lakes. Increase in the water and organic substances supply from the permafrost active layer, precipitation and groundwater can be predicted due to the observed climate warming.

The ecosystems of Yamala lakes poor in organic matter (OM) in general, but OM increase may occur due to hydroclimatic factors, permafrost degradation and additional OM flux to objects while intensification of eutrophication processes. However, the photodegradation and high accumulation exchange capacity of bottom lacustrine sediments indicates the presence significant relaxation period of ecosystem under external influences.

Decrease in ice thickness by 15-20 cm in 2040-2051 relative to the values of 2009-2021 is predicted for two thermokarst lakes according to RCP 2.6 and RCP 8.5. The lake bottom water temperature will increase by 1-2°C both during open water and under ice. The thermal balance of the bottom sediments and taliks will be positive, and increase of volume of talik will be contributed.

Three main paleoclimatic periods of sedimentation over the past 500 years have been identified based on the dating of lacustrine deposits and the description of their geochemical and spore-pollen features (the rate of sedimentation in the Neytinskiye lakes is an average of 0.8 mm/year, method for determining 210Pb): (1) 500-450 years - active sedimentation with high values of K, V, Ba; (2) 450-100 years - uniform sedimentation with low element’s concentrations, which can be interpreted as a general cooling and an erosion decrease on the lakes catchment; (3) 60-100 years - is a warmer period with waterlogging and increase of Mn and Fe and biogenic elements entry from the catchment due to the degradation of permafrost. A peak of Al and Zn can be interpreted as a result of anthropogenic impact.

Geochemical analyses were carried out on the equipment of the SPBU Resource centers "Magnetic Resonance Research Methods" and "Methods for the Analysis of Substance Composition." Research on the Yamal lakes will be continued with the support of the Russian Ministry of Science and Higher Education, agreement No. 075-15-2021-139