Clay Mineralogy of Gelic Soils from the Fildes Peninsula, Maritime Antarctica

The general physical and chemical properties of Antarctic soils have been long studied, although detailed soil mineralogy remains comparatively little explored. The aim of this study was to characterize the clay mineralogy of soils from Fildes Peninsula, King George Island, Maritime Antarctica. The clay fraction of four soil profiles was studied by x-ray diffraction (XRD). Poorly crystalline mineral phases were sequentially treated with 0.1 mol L-1 sodium pyrophosphate, 0.2 mol L-1 ammonium oxalate, and 0.5 mol L-1 NaOH. After each extraction, differential XRD patterns were obtained. The presence of primary minerals in the clay fraction, such as K-feldspar, plagioclase, pyroxene, and mica, indicates the low degree of chemical weathering. However, ornithogenic influence leads to the phosphatization of the mineral substrate and neoformation of secondary phosphates containing Fe and Al, such as leucophosphite, metavariscite, and minyulite. Overall, what makes these Antarctic soils unique is (i) the widespread occurrence of poorly crystalline minerals in the clay fraction with concentrations ranging from 20.9 to 65.6%, (ii) their association with organic matter forming organo-metallic complexes, and (iii) Al- and Si-rich oxides (allophane and imogolite) and poorly crystalline Fe oxides. Such high amounts of poorly crystalline mineral phases can compensate for the generally low clay content, favoring the retention of ionic and polar chemical compounds, including pollutants.