Mineralogy and chemical composition of Cryosols and Andosols in Antarctica

Variations in mineralogical and elemental composition of Turbic Cryosol (King George Island and James Ross Island), Skeletic Cryosol (J. Ross Island, the Trinity Peninsula), Leptic Andosols (Deception Island), and Skeletic Andosols (Deception Island) were studied. Significant differences in mineralogical composition in size fraction, vertical and horizontal position were determined by X-ray diffraction quantitative analysis. The differences were attributed to a variable degree of chemical weathering process. As a product of weathering were defined montmorillonite, chlorite, microcrystalline polymorphous silica, Fe oxides, and oxyhydroxides. Their content was increased towards the surface and in a finer fraction. Crystal thickness and size distribution of montmorillonite was measured by the Bertaut-Warren-Averbach technique and the results confirmed higher intensity of chemical weathering in Turbic Cryosols (J. Ross Island and King George Island). Feldspars and volcanic glass were the main phases found in soil samples from Deception Island. They were determined as phases of parent rock and indicated low intensity of chemical weathering. Clinoptilolite was identified in soil samples from J. Ross Island and Deception Islad and its hydrothermal origin was supposed. Soil (sample AP) from Base General Bernardo O'Higgins Riquelme had significantly higher content of phosphate minerals, which was a result of ornithogenic activities. Macro elements content was consistent with mineralogical analyses. Turbic Cryosols were rich in iron, aluminium, magnesium, and manganese (> 2%). Skeletic Cryosols contained also iron, aluminium, magnesium, manganese, calcium, and sulphur (> 1%). Leptic Andosols were rich in iron and aluminium (> 2%). Soil properties and humic substances quality were evaluted. Results of chemical and physical analyses indicated that poorly developed soils of Antarctica varied in acidity, conductivity, humus content, and texture. Humic substances content and quality were low. Mainly mechanical (physical) and chemical weathering processes played major role in the soil development accompanied by low intensity of biological activity.