GAS COMPOSITION AND MICROORGANISMS OF GROUND ICE IN RUSSIAN ARCTIC

Abstract

Link for citation: Butakov V.I., Slagoda E.A., Zavatsky M.D., Ivanov V.I. Gas composition and microorganisms of ground ice in Russian Arctic. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 63-75. In Rus. Relevance. The increase in the concentration of greenhouse gases in the atmosphere is a fundamental problem on a planetary scale. The source of greenhouse gases in the subsurface horizon of soil can be both deep deposits of hydrocarbons and organic matter processed by microorganisms during the thawing of the ice-rich soil. To determine the source of the gas it is necessary to examine both its quantity and composition and the microorganism content in the subsurface ice. Taking into account the dynamic development of the energy complex in the north of Western Siberia it is necessary to take into account the geotechnical risks associated with the release of greenhouse gases from frozen deposits. Purpose: to study the composition and identify the sources of greenhouse gases in the ice and the ice-rich soil on account of the ice formation conditions and the microorganism content. Objects: ice wedge, hydrogenic and segregational genesis of ice, ice-rich soil of northern Western Siberia and Central Yakutia, collected by expeditions Earth Cryosphere Institute, Tyumen scientific center SB RAS in 2011–2021. Methods of research and interpretation of chemical composition. The structure of frozen deposits has been investigated by cryolitological methods. The monoliths of the ice and the frozen deposits were stored at –18 °C. Gas was extracted from the monoliths with the determination of volume fraction by thermovacuum degassing method. The composition of gases is determined by gas chromatography. Normalization of the gas composition with solubility values in water was carried out. Volume fractions of gas in free and dissolved forms was calculated. The data processing were implemented by means of «Geochem Anomaly» program. Cultivated psychrophilic microorganisms were studied by seeding on nutrient media; the total number of microorganisms was determined by epifluorescent microscopy. Results. The contents of N2 (74,9–87,8 %), O2 (11,7–20,3 %), CO2 (0,01–3,28 %), CH4 (0,003–7, 35 %), H2 (0,001–0,035 %) and hydrocarbons with an atom content from 2 to 6 (2,0×10–5–2,8×10–3 %) are determined in ice and ice-rich soil. The value of N2 and O2 in the gas composition of ice is close to atmospheric air. The ice has wide variations in gas saturation (1,1–21,1 %), CH4 and CO2 content. The freezing of gas-saturated solution occurred for the ice formation, part of the air was in a free form (from 30 to 75 %). Calculated indexes CH4/(C2H6+C3H8) and C2H6/C2H4 indicate biogenic hydrocarbon genesis. The composition of gas bubbles is recalculated for the volume of the entire sample: CH4 content is insignificant in ice wedge, closed-cavity ice and icing (averages 51, 81 and 1 ppmV, respectively). The low amounts of CH4 could be produced by forming these types of ice from the sediments of the active layer, as the dependence of the gas composition on the peat element amount is established. CH4, CO2 and H2 contents increased in samples with peat elements. In interbedding ice the CH4 content is high (216 ppmV). CO2 (up to 3007 ppmV) was accumulated in the texturing ice, and hydrogenic wedge-shaped ice showed high levels of CH4 (up to 4032 ppmV) as the ice was frozen in an enclosed volume. The ice of peat mound has a maximum content of CH4 (15545 ppmV) and high CO2 (2466 ppmV); inclosing sediments flooded with marginal-marine waters are the source of high values of CH4 and CO2. The cultivated psychrophilic microorganisms were identified in the surface ice, and their maximum quantities were identified in segregated formations – up to 1680 KOU/ml, in textural ice – up to 1032 KOU/ml. High concentrations of greenhouse gases are found in frozen peat – CO2 (1075 ppmV), H2 (9 ppmV), CH4 (262 ppmV) and other hydrocarbons due to activity of microorganisms, which results in accumulation of these gases. High gas saturation and CH4 and CO2 levels indicate the formation of gaseous composition by both aerobic and anaerobic microorganisms.