Cryopedology

The term “cryopedology” is derived from the Greek words cryos (“icy cold”), pedon (“soil”), and logos (“study”) and, hence, refers to the study of frozen ground and intensive frost action. Although cryosols were studied for many years in Russia, Nikiforoff (1928) introduced the concept of frozen ground and intensive frost action to the English-speaking world. He provided a historical overview of permafrost, a map showing the distribution of permafrost in Eurasia, a summary of data regarding permafrost thickness, and its relation to present-day and paleo-climates. Kirk Bryan (1946), the American geomorphologist, introduced “cryopedology” as the study of frozen ground and intensive frost action. In 1949, the French geomorphologist André Guilcher traced the development of cryopedology. Cailleux and Taylor (1954) published Cryopedology: the Study of Frozen Soils as part of the French polar expedition to Greenland.

In this book the view is taken that the permafrost-affected soil is comprised of three parts: the active layer, the transition layer, and the permafrost layer. Soil formation is especially pronounced in the active layer but also occurs in the transition from warmer periods. The active layer varies from 0.1 m in high latitude environments to more than 10 m in low-latitude mountains. The active layer shows the maximum degree of cryoturbation, may contain high amount of organic C, often is dense from merging of freezing fronts, and may exhibit dilatancy in silt-rich soils. The transition layer displays many of the same properties as the active layer, including high amounts of segregated ice, cryoturbation, and abundant soil organic C. Permafrost represents a condition in which a material remains at or below 0 °C for 2 or more years in succession. Permafrost may be over 1,500 m thick in central Siberia. Dry-frozen permafrost is a peculiar form of permafrost that occurs in hyperarid regions of Antarctica. The nature of segregation ice in permafrost is important for determining its mechanism of formation.

In addition to the usual properties described in low-latitude soils, properties that are unique to cryosols that should be described include patterned ground, cryoturbation features, the depth to the top and bottom of each horizon (for broken horizons), cryostructures, and the depth to and nature of permafrost. Sketches or field-ready photographs are recommended for diagramming soil horizons, cryoturbation, and other features. There are no universally accepted guidelines for delineating soil horizons; Table 3.2 compares horizon symbols used in the US, Russian, Canadian, and WRB systems.

The preferred time for sampling cryosols is at the end of the summer, because the active layer is deepest at that time. Sampling earlier requires power tools to get to the base of the soil profile and a correction to be made for the end-of-season thickness of the active layer. Three kinds of samples normally are collected from cryosols: bulk samples for routine analysis, minimally disturbed volumetric samples for bulk density and water retention, and thin-section samples for micromorphological analysis. Physical, chemical, mineralogical, and micromorphological analyses are normally performed for cryosols as with all soils.

Climate is the most important factor influencing development of cryosols. There is a wide variety of climates for cryosols that ranges from maritime to continental. The mean annual air temperature ranges from +1 °C to −20 °C or colder; the mean annual precipitation ranges from <10 mm in interior Antarctica to more than 2,000 mm in high-mountain environments. High winds are common in many areas with cryosols. There is a variety of vegetation in the cold regions, but they are largely treeless except in the boreal forest or taiga. Birds transfer large amounts of nutrients from the coast to land in areas fringing the Arctic and Southern Oceans. Patterned ground is a common landform component in areas with cryosols. These features may be sorted in circles, nets and stripes, or they may be unsorted in the form of ice-wedge polygons, frost boils, and earth hummocks. The most common parent materials are eolian (loess and sand dunes), alluvium, lacustrine, peat, colluvium, gelifluction materials, and beach sediments. These materials may be of recent age or may extend back as far as the Miocene.

Although soil-forming processes, such as humification, paludification, podzolization, and gleization operate in cryosols, the dominant processes are of cryogenic origin. Cryogenic processes involve inputs, outputs, transfers, and transformations of energy, water, and soil material and, therefore, according to classical definitions of soil-forming processes. Cryogenic processes include frost heaving, cryoturbation, dilatancy, cryodesiccation, and ice segregation. These processes are evidenced at the landscape scale in the form of patterned ground, at a pedon scale in the form of cryoturbation, dilatancy, ped forms, and cryodesiccation features, and at the microscopic scale from compaction, displacement of plasma or skeletal grains, and pore formation. Cryopedologic processes are utilized in the definition of cryosols or gelisols and at the second highest level in distinguishing whether or not cryoturbation is observed in mineral soils. Numerical models of cryopedogenesis have focused on specific processes such as heaving, formation of segregation, and cryoturbation.

Cryosols cover about 13.8 million km² worldwide, of which 83 % occur in the circumarctic and 17 % in mountains of the high latitudes and high mountains. Because the active layer is too deep (>1 or 2 m) in mountains with permafrost and in the sporadic and isolated permafrost zones of the circumarctic, only 63 % of the permafrost region contains cryosols. The other soils are Entisols, Inceptisols, Histosols, and other soil orders.

The circumarctic region contains 11.4 million km², or 83 % of the cryosols worldwide. The climate of the circumarctic varies geographically and is determined by proximity to oceans, elevation, and latitude. Most of the circumarctic contains continuous permafrost. However, discontinuous, sporadic, and isolated permafrost may occur in the Low Arctic. Active-layer depths range from 0.4 to 2.0 m in the Low Arctic, from 0.4 to 1.0 m in the Mid-Arctic, and from 0.25 to 0.9 m in the High Arctic. Common vegetation types in the Arctic are erect shrub land, peaty graminoid tundra, barrens, mineral graminoid tundra, prostrate-shrub tundra, and wetlands. The relief in the circumarctic commonly is flat to undulating with elevations generally below 500 m. Patterned ground is ubiquitous in the Arctic. Cryosols in the circumarctic have been derived from a variety of parent materials, including marine and lacustrine, glacial, windblown, colluvium, and residuum.

Common soil properties of Arctic soils are permafrost within 1–2 m of the surface, cryoturbation, cryodesiccation, and accumulation of segregated ice. Chemical and physical properties vary significantly in response to the action of the soil-forming factors, but the accumulation of organic matter and the development of redoximorphic features are common.

There is a strong latitudinal gradient in soil-forming processes in the Arctic. As one progresses to the north, there is a reduction in redoximorphism (gleization), melanization (organic matter accumulation), podzolization, and textural differentiation and an increase in latitude and an increase in calcification, salinization, and desert pavement formation as the climate becomes more arid.

Only 0.35 % of Antarctica is ice-free, amounting to an area of 49,500 km². There are three distinct climatic zones in Antarctica. The western Antarctic Peninsula and the offshore islands (South Shetland and South Orkney Islands) have a subantarctic maritime climate with comparatively mild temperatures and abundant precipitation, including rainfall. Coastal East Antarctica has cooler temperatures and less precipitation, all of which falls as snow. The inland mountains feature hyperarid and hypergelic conditions. These climate differences are reflected in active-layer thickness and mean annual ground temperatures, which are greatest in maritime Antarctica and least in the mountains. Birds, especially large penguin colonies, play an important role in soil formation and in the ability of sites to become colonized by vegetation. Whereas soils in maritime and East Antarctica tend to be of Last Glacial Maximum or Holocene in age, soils of inland mountains commonly range from mid-Pleistocene to Miocene in age.

The climatic zonation is reflected in the nature of the soils. The amounts of silt and clay, organic C, total N, extractable P, and soil moisture and soil temperature decline from the West Antarctic Peninsula to East Antarctica and then to the inland mountains. Whereas soils of maritime and East Antarctica are often very strongly acidic and low in base cations and soluble salts, soils of the inland mountains are alkaline, strongly base saturated, and contain abundance salts.

The total area of alpine permafrost may be 3.6 million km² but there are only 2.3 million km² of alpine cryosols. A mean annual air temperature of −5 or −6 °C may be necessary for the active layer to be within 1–2 m of the ground surface in alpine regions. Many alpine plants are circumpolar, meaning that they occur throughout the Arctic and mountains at lower latitudes in the Northern Hemisphere. The properties of alpine cryosols are highly variable, much like Arctic and Antarctic cryosols. The dominant soil-forming process in alpine cryosols is cryoturbation; other processes of importance include andisolization, melanization (humification), cambisolization, podzolization, paludization, and gleization. Alpine cryosols occur primarily in the mountains of Arctic regions, but they also occur at high elevations in the mountains of central Asia. Alpine cryosols are comparable to Arctic cryosols, except that they contain considerably less organic C.

Cryosols have played an important role in understanding Earth’s systems, including relative dating of soil parent materials, correlating geologic deposits, understanding glacier dynamics, reconstructing past environments, preservation of artefacts and microorganisms, detecting paleo-human occupation sites, predicting soils and geomorphic surfaces on extraterrestrial planets such as Mars, and determining whether or not high level lakes existed during the early Holocene in the McMurdo Dry Valleys.

The high-latitude and high-elevation cryosols are experiencing some of the greatest warming over the past several decades of anywhere on Earth. This has resulted in increases in active-layer thickness in low Arctic and alpine cryosols and an increase in permafrost temperatures. There have already been reports of changes in soil properties and processes and continued changes can be expected.

The key land uses in Antarctica are establishment of scientific bases and tourism. These activities have had localized impacts in terms of petroleum spills and release of toxic chemicals.

In the Arctic key land uses are subsistence living, oil and gas extraction, mining, and more recently tourism. Land degradation in the Arctic is manifested by spills of petroleum products from pipelines, soil and water contamination from mining, removal of timberline forests, and removal of sand and gravel for access roads and pads for pumping stations. Key land uses in areas with mountain permafrost include mining, recreation, limited agriculture, and highway-railway construction. Land degradation in alpine regions with permafrost include erosion and mass wasting from cutting of subalpine forests, flash floods from melting of permafrost, soil and water contamination from mining and mining waste disposal, and the after-effects from radioactive fallout from the Chernobyl disaster.

Soil databases are collections of soil information organized in systematic form in an electronic environment. They include both spatial databases, which contain soil information that can be displayed as soil maps, and point databases, which contain morphological, physical and chemical data for a pedon at a specific location. In addition, numerous soil databases contain monitored data on soil temperatures, soil moisture, and active and thaw layer depths. Since the soil databases are in an electronic form, they are very useful for various interpretations, scaling up information such as carbon concentrations and carbon stocks, and providing basic information for modeling.