Protosoils of the Polar Regions: A Study of Organic and Mineral Components with the Use of Raman Spectroscopy

Abstract Protosoils with cryptogamic-microbial organogenic horizons occupy a significant part of land and are most noticeable in areas with extreme conditions (Antarctica, High Arctic, highlands, and hot deserts), i.e., in the regions, where the development of vascular plants is suppressed or impossible. The latter determines a specific set of soil formation products, as well as the processes of organic matter accumulation and transformation. Given the specific microstructure of protosoils with microbial horizons, their study requires sensitive non-destructive methods with a high spatial resolution. Raman spectroscopy, which is successfully used to study interactions between microorganisms and minerals, is one of the promising methods for this purpose. Here, we explored organic and mineral components of endolithic and hypolithic protosoils from East Antarctica and Severny Island of the Novaya Zemlya Archipelago. Crystalline polymorphic modifications of calcium carbonate (calcite and aragonite), gypsum, calcium oxalate (whewellite), polyenes (carotenoids), hematite, and goethite have been identified. A set of bands indicating combinations of Fe oxide-hydroxides and carotenoids, as well as CaCO 3 and carotenoids have been encountered in the Raman spectra, which suggests stable spatially localized associations of these compounds in a volume of about 1 µm 3 . It is assumed that in situ weathering of Ca-containing silicate minerals played an important role in the formation of CaCO 3 on non-carbonate rocks (gneisses). It is demonstrated that complex microhorizons with a possibility for long–term carbon stabilization—removal of C from rapid biogeochemical cycle in the form of both organic and inorganic compounds—are formed in the protosoils.