ИСТИНА

Recent climate warming has caused rapid thawing of Arctic glaciers and the development of soil-forming processes on freshly exposed substrates. Sediments that have accumulated over the lifetime of these glaciers have mostly aeolian genesis and include both minerogenic and biogenic components. Such sediments are termed cryoconites and act as a storage of organic carbon within glaciers formed during the Pleistocene-Holocene. The retreat of glaciers is accompanied by the release of cryoconite material into water flows that carry and deposit such material usually within areas sheltered from winds. In comparison to other deposits within the modern periglacial zone of the Arctic, the cryoconite parent material of soils has special properties such as a high content of biogenic compounds and fine texture, which favour the colonization by higher plants and the development of pedogenesis. The study sites were located within the glacio-nival system of the rapidly retreating Aldegonda Glacier (its snout was reduced by 2 km in the last 100 years) and on third marine terraces of the East-Fjord in Svalbard, Norway (77.98 N, 14.11 S). The objects studied were as follows: (1) soils formed on moraines of different ages (free from glacial ice for either 18, 70 and over 100 years), (2) fine earth and moss residues in cryoconite holes on glacial ice surface and (3) soils on marine terraces that were free from glaciers for the entire Holocene, according to palaeogeographic data, and, therefore, unlikely to contain any carbon of cryoconite origin. Data were obtained on C and N contents (dry combustion), C and N isotopic compositions, radiocarbon ages of TOC and of densitometric fractions and magnetic properties (NMR-spectroscopy). Results of this study led to the conclusion that cryoconites served as a source of organic matter for the soils on moraines and, as was shown by the radiocarbon dating, such organic matter was originated from deep layers of the rapidly thawing glacier. In soils formed either with or without cryoconite material, densitometric fractions with >1.6 g/cm3 densities were older than light fractions. In soils with cryoconite material the heavy fractions were dominant and significantly more ancient than in soils without such material. Thus, carbon deposited by glaciers thousands of years ago has been included into carbon exchange cycle, with its properties being retained for over hundred years.