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

Abstract

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 palaeoenvironmental 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 an excellent pedo‐signature of different specific past climatic/environmental conditions. In this study, we performed a detailed chemical characterisation of the organic material found in palaeosols, 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 into different pools by means of density fractionation, in order to separate the more fresh/unaltered free and occluded organic material (Light Fraction) from the stable fraction chemically bound to the mineral phase (Mineral Organic Matter—MOM). To better characterise 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 characterised 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 was stored in the stable MOM pool, characterised 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 palaeoenvironmental reconstruction at the Stolenberg Plateau, which represents a Lateglacial Alpine Nunatak, and has acted as biological refugia (at least) since the end of the LGM. Highlights The origin and composition of ancient organic matter from a high‐elevation Alpine Nunatak were uncovered. More than 90% of organic carbon was stored in the stable mineral organic matter (MOM) pool. Based on NMR and FT‐IR spectra the MOM fraction consisted of paraffinic substances (37–50%), cellulose and hemicellulose (29–37%). The organic matter originated from ancient alpine tundra that developed on the Nunatak since the end of the Last Glacial Maximum.