Clay Mineralogy in Arctic Tundra Gelisols, Northern Alaska

Little is understood about chemical weathering processes in Alaskan arctic sods, where moisture is generally not limited bill acidity varies and the average sod temperature is close to or below freezing. Weathering reactions in soil convert primary minerals into secondary clay minerals. Silty loam textured soils from three sites in moist acidic tundra (MAT) and three sites in moist nonacidic tundra (MNT) in the northern Arctic Foothills, Alaska, were characterized with emphasis on the origin of the clay minerals. The MNT soils had a discontinuous and thinner organic layer, which leads to a deeper summer thaw and greater cryoturbation than the MAT sods. The MNT had higher cation exchange capacity and base saturation than MAT. These buffer against acidification and account for the pH differences of MAT and MNT. Other chemical characteristics including C and N content as well as Fe and Al were similar (by horizon) across the MAT/MNT boundary. X-ray diffraction of coarse (0.0002-0.002 mm) and fine clay (<0.0002 mm) fractions indicate that illite, vermiculite, and kaolinite are the predominant clay minerals. Presumably, kaolinite is detrital and vermiculite is weathered from illite. The proportion of vermiculite to illite is higher in MAT and the illite to vermiculite proportion is higher in MNT. This shows that soil acidity does affect weathering processes despite the low soil temperature.