Origin and characteristics of ancient organic matter from a high-elevation Lateglacial Alpine Nunatak (NW Italy)

In high-mountain areas, Pleistocene glaciations and erosion-related processes erased most of the pre-existing landforms and soils. However, on scattered stable surfaces, ancient soils can be locally preserved for long periods, retaining valuable paleoenvironmental information. Such relict surfaces survived during glaciations either through coverage by non-erosive, cold-based, ice or as nunataks. Thus, soils preserved on such surfaces retain excellent pedo-signature of different specific past climatic/environmental conditions. In this study, we performed a detailed chemical characterization of the organic material found in paleosols, discovered inside periglacial features on a high-elevation Lateglacial Alpine Nunatak (Stolenberg Plateau), above 3000 m a.s.l. (NW Italian Alps). The soil organic matter (OM) was separated in different pools by means of density fractionation, in order to separate the more fresh/unaltered free and occluded organic material (Light Fraction-LF) from the stable fraction chemically bound to mineral phase (Mineral Organic Matter - MOM). To better characterize the MOM fraction, this was further subjected to chemical fractionation, in order to separate the alkali-extractable OM (ext-MOM) from the fraction intimately bound to minerals. The obtained fractions were then characterized by chemical and 13C nuclear magnetic resonance (NMR), and Fourier Transform Infrared (FT-IR) spectroscopy. The results indicated that the largest part (>90%) of organic carbon (OC) was stored in the stable MOM pool, characterized by a high degree of decomposition and consisting mainly of paraffinic substances, such as lipids and waxes (37-50%), cellulose and hemicellulose (29-37%). The OM likely originated from autochthonous, well-adapted, ancient alpine vegetation (alpine tundra) that grew on the Plateau during warm climatic phases since the end of the Last Glacial Maximum (LGM). These results further strengthen the paleoenvironmental reconstruction at the Stolenberg Plateau, which represents a Lateglacial Alpine Nunatak, and has acted as a biological refugia (at least) since the end of the LGM.