Micromorphology of ornithogenic soils and its paleoenvironmental implications in the Victoria Land, Antarctica

Ornithogenic soils retain relevant information regarding the history of Adelie penguin colonization and settlement in the Antarctic region. Studies on present and past penguin colonies extension and distribution also furnish significant data to understand global environmental changes, with particular attention to the ecological factors that limit penguin presence and population dynamics. In order to better characterize the ornithogenic soils located along the Victoria Land coasts and to acquire new information on paleoenvironmental development of the region, this work focuses on micromorphological characterization of nine radiocarbon-dated ornithogenic soils, covering a period of approximately 40 kyr, and located in key sites of this region. The detailed micromorphological study of 58 thin sections, was carried out at the optical petrographic microscope and supported by SEM-EDS and XRD analyses of samples belonging to ornithogenic soils from the Victoria Land coasts. All the soils studied have some common characteristics, mainly related to the layers of ornithogenic material (e.g., the presence of rock fragments transported by birds to construct their nests, the remains of birds or evidence of bird activity, and the notable phosphorus content), with some peculiarities between the different profiles, indicating the presence of a local micro-variability (e.g., the relative abundance of water-driven pedofeatures, both illuvial and microcrystalline, and also of frost-related pedofeatures). This study allows these soils to be regarded as ornithic arenosols/cryosols/regosols/gelisols, and, in addition, it highlights the differences between ornithogenic soils developed in the Victoria Land compared to those described in the Maritime Antarctica. Different microstructures and pedofeatures (i.e., a weaker microstructural development, a less pronounced mixing between mineral and organic components, a less aggressive process of phosphatisation and also a lower frequency of frost-induced pedofeatures in Victoria Land ornithogenic soils) seem to be related to the reduced availability of liquid water in Victoria Land and most probably reflect different climatic/environmental conditions respect to Maritime Antarctica, since at least the deglaciation after the Last Glacial Maximum (LGM). Our results demonstrate that ornithogenic soils represent a powerful proxy for characterizing past and ongoing environmental condition in the coastal areas of Antarctica, and, furthermore, they offer new opportunity to study pre- LGM relict soils, which survived the overriding of the Antarctic Ice Sheet along the Victoria Land coast.