ELEMENTAL COMPOSITION OF BOTTOM SEDIMENTS OF THERMOKARST LAKES IN THE NORTH OF WESTERN SIBERIA (THE CASE OF THE PUR-TAZ INTERFLUVE)

Abstract

The degradation of permafrost leads to changes in the biogeochemical cycles of carbon, nutrients, and metals in the aquatic systems of permafrost landscapes. The characterization of the chemical composition of bottom sediments plays a key role in analyzing changes in element fluxes in Arctic lake systems. This study deals with the granulometric and elemental composition of bottom sediments and soil-forming rocks in the catchment areas of small thermokarst lakes in the southern part of the Tazovsky Peninsula, between the Pur and Taz Rivers (West Siberian Plain). The elemental composition was determined by inductively coupled plasma mass spectrometry (ICP-MS), the granulometric composition – by laser diffraction, the organic carbon content – by high-temperature catalytic oxidation. The conditions in the littoral zones of water bodies under the influence of cryogenic processes lead to a change in the ratio of size fractions toward an increase in the proportion of larger fractions and accumulation of less sorted material. Among the rock-forming elements, soil-forming rocks and bottom sediments are depleted in Al, Fe, K, Na, Ca, Mg relative to the upper continental crust, while soil-forming rocks are rich in titanium and bottom sediments – in total sulfur. Bottom sediments were found to be moderately rich in cadmium and total sulfur relative to the upper continental crust. The elemental composition of bottom sediments of thermokarst lakes of the Pur-Taz interfluve generally inherits the composition of rocks in the catchment areas and is formed in close connection with them, this demonstrating the influence of mainly rock and lithogenic factors. The influence of the facies factor is manifested in the accumulation of organic matter, total sulfur, and chalcophilic elements. The accumulation of total sulfur in bottom sediments may be the result of sulfate reduction in detritus. The depletion of bottom sediments in certain elements relative to parent rocks may be due to their individual chemical properties and forms of occurrence as well as the grain size distribution of the sediments.