Evaluation of stabilization rate of high and low molecular organic matter in cryoconite holes from the Arctic, Antarctic and Caucasus mountain ecosystems by 13C–NMR spectroscopy

Cryoconite holes are considered as a place of accumulation of organomineral matter, including black carbon. It is formed as a result of incomplete combustion of carboncontaining fragments of natural and anthropogenic origin. Such material is transported by the wind and participates in the formation of cryoconite on the ice surface. The accumulation of organic matter in cryoconite can significantly affect the climate of our planet. To assess the processes of resistance to biodegradation of organic matter in cryoconite, molecular methods of analysis were used. This work presents the qualitative and quantitative evaluation of composition of humic acids, formed in selected cryoconite holes of various geographical regions. To identify them, the 13C–NMR spectroscopy method was used, which makes it possible to reveal trends in the accumulation of specific structural fragments and the rate of stabilization of cryoconite organic matter. The analysis of the elemental composition revealed that the most condensed macromolecules of humic acids accumulate in cryoconite holes on Mount Elbrus. In the molecules of humic acids, the accumulation of aliphatic structural fragments up to 71-73% occurs to a greater extent, while the composition of the aliphatic fragments depended on local precursors of humification. In the Arctic and Antarctic ecosystems, humic acids with relatively homogeneous composition are formed. These ecosystems are characterized by the domination of moss-lichen communities, which are characterized by a predominance of lipids and carbohydrates in the chemical composition. Black carbon is an important part of the planetary carbon cycle. Under the conditions of active deglaciation, cryoconite material can enter the periglacial zone, and under the action of soil microorganisms, it can become an additional source of greenhouse gases in the atmosphere.