“Ice carbon” as a possible source of apparent age in paleosol dating

Surface and buried paleosols are a significant archive of information about environmental change and are widely used in paleogeographic reconstructions. Soil features and their profiles change over time as a result of environmental change. The soil memory is the palimpsest-like, as opposed to the book-like, sedimentary record (Targulian and Goryachkin, 2004). The palimpsest-like memory of the soil requires informed and well-adapted strategies for deciphering and interpreting the information it contains. The question of soil age and its synchronization with reconstructed events remains one of the most controversial issues in paleosol interpretations. The complexity of the interpretation of obtained radiocarbon dates is related to the heterogeneous and heterochronous of soil organic matter (SOM). At present, there are many approaches to dating SOM, but for the paleosol for paleogeographic reconstructions, ¹⁴C dating is most often performed on total organic carbon (bulk carbon). This choice of dating fraction is usually related to the poor preservation of SOM and its low carbon concentration in paleosols. Dates obtained for SOM in buried soils are based on the assumption that SOM was formed "in situ". However, due to various natural processes, paleosols can contain carbon from a number of potential sources.
For buried soils formed in periglacial landscapes, a significant source of carbon is the supraglacial material: cryoconites and other organo-mineral formations that form on the surface and in the body of the glacier and enter the landscape during glacial melting. Our studies on glaciers and in periglacial landscapes of different natural zones (Svalbard, Franz Josef Land Archipelago, Polar Urals, Altai, Kamchatka) have shown that supraglacial material can have a radiocarbon age ranging from modern to very ancient (several thousand, sometimes tens of thousands of years). The largest dataset we have obtained for supraglacial objects is represented by carbon pools aged 1000 to 10,000 radiocarbon years, BP and >10,000 radiocarbon years, BP. The pool with an age of >10,000 radiocarbon years is associated with the presence of a "dead carbon" source near the studied glacier. Dates in the range of 10,000-20,000 radiocarbon years may also reflect the age of soils and sediments formed during the last deglaciation and buried within the body of the glacier as it advanced. Soils formed in the periglacial zone inherit the isotopic composition of SOM from supraglacial material and become carriers of "apparent" / inherited ¹⁴C age. The presence of cryoconite material in buried paleosols can be diagnosed by studying their micromorphology and identifying morphological structures characteristic of cryoconites. We have shown this for soils formed on cryoconite material in Svalbard and for lenses of buried fine-grained material in marginal glacial formations (Keiva) on the Koly Peninsula.  When ¹⁴C dating paleosol series (traditional paleoarchives are studied in foothills and mountainous areas), it is necessary to consider the ice-carbon contribution to SOM in order to make correct paleo-reconstruction.