The sSate Factors of Soil Formation in Arctic Tundra.
Chien-Lu Ping1, Gary Michaelson1, F. Stuart Chapin2, John Kimble3, Walter Oechel4, Yuri Shur5, Charles Tarnocai6, and Donald A. Walker5. (1) University of Alaska Fairbanks Palmer Research Center, 533 E. Fireweed Ave., Palmer, AK 99645, (2) Institute of Biology, University of Alaska Fairbanks, 127 AHRB, Fairbanks, AK 99775-7000, (3) USDA-NRCS-NCSS retired, 151 East Hill Church Road, Addison, NY 14801, (4) San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4614, (5) University of Alaska Fairbanks, 237 Duckering, Fairbanks, AK 99775-5900, (6) Agriculture and Agri-Food Canada, K.W. Neatby Building, Room 1135, 960 Carling Ave., Ottawa, ON K1A OC6, Canada
Although the state factors of soil formation according to Jenny, including parent material, climate, organisms, topography, and time, apply to all geographic regions, the relative weight of each factor varies according to the specific environment. Parent materials in the Arctic vary widely from residual, colluvial, glacial, alluvial, marine, and eolian deposits. The nature of these deposits controls soil physical and chemical properties. However, due to the low rate of weathering in the arctic region, the primary minerals in the parent materials are least altered. The climate of the arctic region is characterized by cold ambient temperatures, short growing seasons, and the presence of permafrost. A unique characteristic of arctic soils is that they contain large amounts of water in the form of ice. The dynamic nature of ice formation accompanied by frost heaving and thermal contraction of frozen soils, and melting of ice with settlement of thawing soils drive cryoturbation, resulting in cryogenic structures at the pedon level and the formation of patterned ground including sorted and nonsorted circles at the landscape level. The climate factor in the Arctic limits biomass production, organic matter decomposition, and other biogeochemical processes in the soil. Biomass production decreases with increasing latitude due to colder temperatures and decreased precipitation, resulting in comparable decreases in soil organic matter accumulation. The presence of permafrost serves as a barrier to root and water penetration. Frost heave and freeze-thaw cycle result in cryoturbated soil and redistribution of soil organic carbon and other nutrients in the soil. In dry coarse textured soils, such as on sand dunes and well drained ridge tops the permafrost contains insufficient ice to cause cryoturbation. In finer-grained soils and on lower slope positions, saturated and reducing conditions often occur above the permafrost due to perched water table during the growing season. Organisms contribute to the accumulation of organic matter due to the cold, wet thus reducing conditions. Vegetation and the surface organic horizons play a critical role in alter the thermal condition of the tundra surface thus modifying the frost boil process. Global warming gases such as CO2 and CH4 not only generated during the growing season but also during winter when soil temperature drops far below freezing point due to presence of unfrozen water that sustains biological activity in the soil. Another unique characteristic of arctic soil is that elements are reduced in the frozen state such as in the permafrost layer. Topography redistributes solar energy and moisture thus affects vegetation community in arctic tundra. Topography controls hydrology that regulates saturation and reducing conditions which in turn affect the rate of organic matter decomposition/accumulation. In Arctic Alaska time left its mark on soil formation in the glaciated areas where soil acidification proceeds with the age of the age of surface. In the non-glaciated Arctic Canada soil acidity does not follow landscape age rather reflects the parent material due to the low weathering rate under the extreme environment. The uniqueness of the state factors of soil formation in the Artic is cryogenesis caused by ice formation in the profile and by the underlying permafrost, and biogeochemical processes at subzero temperatures.