Key chemical characteristics of cryoconite sediments from Bezengi glacier and local mountain soils in the Caucasus mountains, Russia

Cryoconite is a dark-colored supraglacial dust which may be found in polar and mountain regions in the world. These sediments represent a combination of mineral particles, black carbon and organic matter. Cryoconite is considered as a microbial hotspot on an uninhabited surface of glaciers as well as material which influence the level of albedo. Due to relatively similar microbiological and physicochemical features of cryoconite it could take part in development of primary soils. This is important because of current rapid deglaciation in the Caucasus region which will intensify due to ongoing climate change.

The purpose of this research is to study physicochemical features of cryoconite, other types of sediments and cryoconite derived periglacial soils in Caucasus region, Kabardino-Balkarian republic as well as local Chernozems. Samples of cryoconite, moraines and mudflows were collected at Bezengi Glacier, the largest valley glacier at the Caucasus mountains. Cryoconite derived soils were collected in the adjacent Khulamo-Bezengi Gorge; Chernozems and fresh mudflow material were sampled at Baksan Gorge. Soil acidity (H₂O, CaCl₂), total organic carbon (TOC), basal respiration values and particle-size distribution were determined under laboratory conditions.

Almost all samples of materials from the Bezengi Glacier as well as Chernozems were characterized by a neutral reaction, while some samples of mountain soils of the Khulamo-Bezengi Gorge were characterized as slightly acidic and acidic, especially with regard to exchangeable acidity. Basal respiration values range from 2.20 mg of CO₂ per day in fresh mudflow to 35.09 mg of CO₂ per day in the upper horizon of mountain soils. In general, relatively high values of basal respiration were typical for mountain soils, which also has been observed in cryoconite from cracks and holes due to high amount of easily accessible organic matter. Most of cryoconite and moraines from the Bezengi Glacier were characterized by a low content of organic carbon (about 0.10%), while in the upper horizons of mountain soils these values were the highest (up to 7.54%) due to input of cryoconite material in soils through water streams in the warm period of the year.

Cryoconite and moraines were characterized by the predominance of coarse earth fraction while soils were characterized by the dominance of fine earth material. The study of particle-size of cryoconites and other materials from the Bezengi Glacier showed the dominance of the sand fraction (d=0.05-1mm). Fresh mudslides from the Baksan Gorge and mountain soils of the Khulamo-Bezengi Gorge were characterized in the same way. Chernozems of the Baksan Gorge were characterized by a high content of silt and clay fractions, which makes it possible to classify them as clay and clay loam.

This work was supported by Russian Foundation for Basic Research, project No 19-05-50107 “The role of microparticles of organic carbon in degradation of ice cover of polar regions of the Earth”.