G04_04

Radiocarbon age of organic matter of supraglacial systems of mountain glaciers using the example of the Garabashi Glacier (Northern Caucasus)

Zazovskaya E¹, Mergelov N¹, Dolgikh A¹, Shishkov V¹, Turchinskaya S¹, Dobryanskiy A¹, Goryachkin S¹

¹Institute of geography RAS, Moscow, Russian Federation

In modern terms, glaciers constitute a large terrestrial biome, unique in that they integrate autotrophic-heterotrophic ecosystems with the most significant contribution from abiotic processes. This view of glacial systems makes it particularly interesting to consider how old carbon can accumulate in glaciers, what its sources are, and what contribution this carbon makes to the formation of ecosystems, including soils, during modern glacial melt. The object of our study is the Garabashi mountain-valley glacier (43o 18' N, 42o 28'E, North Caucasus). Between 1997 and 2020 the glacier decreased by 27%. The content of organic carbon, nitrogen, their isotopic composition, and radiocarbon age (AMS) were determined in the  cryoconite, moraines and soils. The resulting radiocarbon ages of the cryoconites range from 850 to 7500 ¹⁴C years BP. It is important to note that we didn’t obtain a modern date for any sample of cryoconite. The age of soil organic matter on the  40 years old moraine is  about 1000 ¹⁴C years BP, indicating an inherited carbon character. The age of organic matter from nearby moraines also varies widely, ranging from 1000 to 4000 ¹⁴C years BP. The obtained data on the age of cryoconites correlate with the results obtained earlier by different researchers for Arctic and Antarctic cryoconites. However, in general there is still no explanation for such an ancient age of cryoconite material. The main problem in the dating and interpretation of radiocarbon data obtained from the cryoconite material is the inability to confidently interpret the source of OM.