Известия Томского политехнического университета: Инжиниринг георесурсов (Nov 2021)
CONTENT AND COMPOSITION OF ATMOSPHERIC AND GREENHOUSE GASES IN UNDERGROUND ICE OF DIFFERENT GENESIS
Abstract
The relevance. The greenhouse effect is often associated with methane and carbon dioxide emission from the thawing gas-saturated icy deposits. The relationship between the increase in concentrations of greenhouse gases in the atmosphere and their content in underground ice and frozen deposits has not been sufficiently studied. Different and incomparable methods of gas sampling from frozen deposits and ice are used to assess the content of gases in sediments and ice, the volume of gases entering the atmosphere. When generalizing the data on carbon emissions in the Arctic zone, it is necessary to take into account both the methods of determining the content and composition of gases and the different chemical composition, the presence of organic and mineral inclusions in genetic types of underground ice. The aim of the research is to determine the results of different methods of gas sampling from ice and to establish the relationship between the content and composition of gases in common genetic types of ground ice. Objects: genesis types of ice (segregated, closed-cavity, and ice wedge), icy frozen deposits of the north of Western Siberia: on the Bely island, on Western Yamal, on the north of Gydan and the Pur-Taz interfluve, collected in expeditions of the Earth Cryosphere Institute, Tyumen scientific center SB RAS in 2014–2019. Research methods and interpretation of chemical composition. The thermal vacuum degassing method and the «headspace» method were used for gas extraction from frozen monoliths and ice. The thermal vacuum degassing method in laboratory conditions with the determination of the gas volume in the ice sample was used as a reference. The method of gas chromatography was applied to determine the composition of atmospheric and greenhouse gases. Gas content in ice and gas content in frozen peat that contains gas in the atmosphere, and the values of the gas solubility in water were compared. The correlation analysis of the gas content in common types of underground ice, as well as frozen peat, was carried out. Results. It was established that gas entrapped in ground ice and frozen peat was similar to atmospheric gas in terms of the relative content of nitrogen and oxygen. It was found out the large variations in methane content from 4 to 1,7×104 ppmV and carbon dioxide from 7 to 2,7×103 ppmV in samples are associated with different conditions for production and accumulation of greenhouse gases in the permafrost. The prevalence of carbon dioxide content over methane in segregated ice and ice wedge was established, and maximum methane concentrations (from 1,1×103 to 1,7× 104 ppmV) in segregated-migration ice of heaving mound and wedge-shaped ice. An excess of methane in the near-surface segregated-migration ice is associated with its accumulation in thawed talik deposits and subsequent ice formation during freezing in a closed system. High concentrations of carbon dioxide (up to 1,1×103 ppmV) and methane (up to 222 ppmV) in segregated ice in peat were found; their source is organic matter degradation under variable aerobic and anaerobic conditions under the action of bacteria. As a result, the peatlands are a significant source of carbon dioxide emissions into the atmosphere. Assessing reproducibility and comparability of the methods of thermal vacuum degassing and «headspace» was carried out in the study of ice and frozen sediments in the cross section of peat bog in the area of the village Gaz-Sale. It was found that methane concentrations during testing by the «headspace» method are overestimated by 3–70 times in comparison with the values determined by the method of thermal vacuum degassing. This is due to the low solubility of methane and its predominance in bubbles, while carbon dioxide and some oxygen remain dissolved in water and do not pass into the gas sample. Consequently, the data on the gas content determined by the «headspace» method is insufficient to estimate the volumes of greenhouse gas emissions, since these values characterize the qualitative composition of the gas in the bubbles. Thermal vacuum degassing method allows calculating and estimating the volumes of gas receipts from thawing permafrost.
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