N. S. Mergelov

Endolithic pedogenesis and rock varnish on massive crystalline rocks in East Antarctica

Desert varnish and endolithic organisms are two widespread phenomena that have been studied in detail separately; their interaction and their genetic relationships have virtually escaped the attention of researchers. Both phenomena are of indubitable interest for pedology: endolithic organisms as an agent of soil formation and rock varnish as a probable product of pedogenesis. It is argued that the system of endolithic organisms, their functioning products, and the rock has all the features inherent to soils: the rock layer subjected to the influence of external abiogenic factors and living organisms dwelling in the rock and synthesizing and decomposing organic substances. The action of biogenic and abiogenic agents leads to the in situ transformation of the rock with the accumulation and removal of the products of this transformation and with the development of vertical heterogeneity in the form of microhorizons composing the soil microprofile. Instrumental measurements indicate that the carbon content in the endolithic horizons developed by biota in granitoid rocks of the Larsemann Hills oasis varies from 0.2 to 3.3%, the nitrogen content in these horizons varies from 0.02 to 0.47%, and the radiocarbon age of their organic matter reaches 480 ± 25 yrs. The products of the pedogenesis are represented by fine earth materials and by abundant and often multilayered films and coatings on the rock surface and on the lower sides of the desquamation (spalling) plates. Scanning electron microscopy with X-ray microprobe analysis indicates that the major elements composing these films are O, C, Si, Al, Fe, Ca, Mg, and S. It is shown that the films of the rock varnish and the organomineral films in the fissured zone of the rock under the plate with endolithic communities have certain similarity in their morphology and composition: the films of the rock varnish also contain biota (dead cells or cells in the dormant state), and their botryoidal structure is similar to the structure of the biofilms inside the endolithic system. In both types of films, amorphous aluminum and silicon compounds are present, and the accumulation of Fe, Ca, Mg, S, Cl, and some other elements takes place. It is argued that some varieties of rock varnish are the products of endolithic pedogenesis; in essence, they represent the horizons of micropaleosols exposed to the surface in the course of spalling and then transformed by the external environmental agents.

Diagnostics of gleyzation upon a low content of iron oxides (Using the example of tundra soils in the Kolyma Lowland)

The matrix of iron (hydr)oxides exerts a decisive influence on the character of gleyzation. Upon a high content of iron (hydr)oxides, their reduction radically changes the horizon color from warm to cold hues, which is typical of soils on the Russian Plain. Upon the low content of iron (hydr)oxides, iron reduction takes place in phyllosilicates with minimal changes in the soil color. The cold hue of cryohydromorphic soils in the Kolyma Lowland is controlled by the color of the lithogenic matrix with a low content of iron (hydr)oxides. In this case, the soil color characteristics expressed in the Munsell notation or in the CIE-L*a*b* system are ineffective for diagnostic purposes. The colorimetric methods appear to be more efficient after the soil pretreatment with hydrogen peroxide, as the gleyed horizons turn green, while the nongleyed (and not overmoistened) horizons turn red. Physical methods (Mössbauer spectroscopy and magnetic susceptibility measurements) are more efficient for characterizing the properties of iron compounds in cryohydromorphic soils as compared with the methods of chemical extraction. Mössbauer spectroscopy proved to be highly efficient, as the iron oxidation index Fe3+/(Fe2++Fe3+) decreases in the gleyed horizons. Chemical reagents (Tamm’s and Mehra-Jackson’s reagents) dissolve Fe-phyllosilicates and are not selective in soils with a low content of iron (hydr)oxides.

Soils of wet valleys in the Larsemann Hills and Vestfold Hills oases (Princess Elizabeth Land, East Antarctica)

The properties and spatial distribution of soils and soil-like bodies in valleys of the coastal Larsemann Hills and Vestfold Hills oases—poorly investigated in terms of the soil areas of East Antarctica—are discussed. In contrast to Dry Valleys—large continental oases of Western Antarctica—the studied territory is characterized by the presence of temporarily waterlogged sites in the valleys. It is argued that the deficit of water rather than the low temperature is the major limiting factor for the development of living organisms and the pedogenesis on loose substrates. The moisture gradients in the surface soil horizons explain the spatial distribution of the different soils and biotic complexes within the studied valleys. Despite the permanent water-logging of the deep suprapermafrost horizons of most of the soils in the valleys, no gley features have been identified in them. The soils of the wet valleys in the Larsemann Hills oasis do not contain carbonates. They have a slightly acid or neutral reaction. The organic carbon and nitrogen contents are mainly controlled by the amount of living and dead biomass rather than by the humic substances proper. The larger part of the biomass is concentrated inside the mineral soil matrix rather than on the soil surface. The stresses caused by surface drying, strong winds, and ultraviolet radiation prevent the development of organisms on the surface of the soil and necessitate the search for shelter within the soil fine earth material (endoedaphic niche) or under the gravelly pavement (hypolithic niche). In the absence of higher plants, humified products of their decomposition, and rainwater that can wash the soil profile and upon the low content of silt and clay particles in the soil material, “classical” soil horizons are not developed. The most distinct (and, often, the only diagnosed) products of pedogenesis in these soils are represented by organomineral films on the surface of mineral particles.

Accumulation of organic matter in the mineral layers of permafrost-affected soils of coastal lowlands in East Siberia

On the basis of a large volume of literature and original data, the high content (1–7%) of organic matter in the mineral layer of loamy permafrost-affected soils of coastal lowlands in East Siberia (from the lower reaches of the Lena River to the lower reaches of the Kolyma River) has been statistically proved. In most cases, the reserves of Corg in the mineral layer of these soils exceed those in the surface organic horizons and constitute 60–90% of the total soil pool of Corg. The enrichment of the mineral layer with Corg is due to the cryogenic retention (retenization) of humus (the illuviation and accumulation of colorless humic substances above permafrost) and the cryogenic mass exchange (mechanical admixture of organic matter from the upper organic horizons into the mineral layers). The analysis of 60 soil profiles showed that the accumulation of organic matter above the permafrost table is observed in 43% of cases; in general, the organic matter distribution in the soil profiles is highly variable. A specific type of colorless humus is accumulated above the permafrost table. The mechanisms of its precipitation and transformation in the profile require further studies.

Windows on Antarctic soil–landscape relationships: comparison across selected regions of Antarctica

Abstract This paper brings together topographic cross-section ‘windows’ from across Antarctica to illustrate soil–landscapes from the margins of the polar plateau in the Transantarctic Mountains and McMurdo Dry Valleys, through East Antarctic coastal areas, to the northern Antarctic Peninsula Region. Soils identified range from Gelisols in the Ross Sea Region, through Gelisols and Entisols in coastal East Antarctica, to a mixture of Gelisols, Entisols, Spodosols and Inceptisols in the northern Antarctic Peninsula Region where permafrost is not ubiquitous. The relative impacts of the soil-forming factors are considered. At a continental scale climate is the main driver of the differences observed between soils in different areas. At local scales strong soil–topographic relationships are observed. Organisms, time and parent material are dominant influences on soil properties only in relatively localized situations. Organisms dominate in areas of organic matter or guano accumulation and time is a dominant influence on exceptionally old upland surfaces in the McMurdo Dry Valleys. The US Department of Agriculture’s Soil Taxonomy gives a useful overall appraisal of Antarctic soils; however, for detailed work, there is a need to introduce some new categories at subgroup level to better capture the range of soils described.

Bacterial communities in the soils of cryptogamic barrens of East Antarctica (the Larsemann Hills and Thala Hills oases)

Bacterial communities from the soils of cryptogamic barrens in the Thala Hills and Larsemann Hills oases of East Antarctica were examined. The total number of bacteria in the studied soils was no higher than 108 cells per gram of soil, which is an order of magnitude lower than the values typically found in the soils of temperate regions. The portion of viable cells reached 60% and more, which attests to the high tolerance of the bacteria to the impact of adverse environmental factors. The maximum values of the total number and viability of the bacteria were found in the fine earth material immediately under the stony pavement. For the first time, the high content of the filterable forms of bacteria (FFB) was found. In some of the samples, their portion reaches 70–80% of the total number of bacterial cells. Data on the high numbers and viability of the bacterial cells and on the phylogenetic and morphological diversity of FFB allow us to attribute the latter to the pool of bacterial cells ensuring their preservation under unfavorable environmental conditions. The concentrations and total pools of bacterial biomass in the studied soils are much lower than those in the zonal soils of temperate regions. Bacterial communities in the studied soils combine the high tolerance toward the adverse environmental factors (as seen from the high portion of viable cells, the formation of the nanoforms of bacteria, and the participation of bacteria in the subaerial biofilms) with the low total number and biomass of the bacterial cells

Soils of MacRobertson Land

MacRobertson Land is the portion of Antarctica lying south of the Mawson Coast between 59° 34′ E and 72° 35′ E. At 5,400 km2, MacRobertson Land constitutes the third largest ice-free area in Antarctica, accounting for 11 % of the total ice-free area. Less than 10 % of the ice area occurs along the coast. It has five major ice-free areas: (i) the Northern Prince Charles Mountains, including the Amery Oasis, (ii) the Southern Prince Charles Mountains, including the Mawson Escarpment, (iii) the Grove Mountains, (iv) a series of small coastal oases and inland Framnes Mountains along the Mawson Coast, and (v) the Vestfold Hills, Rauer-Bolingen Islands, and Larsemann Hills along the Ingrid Christensen Coast. Elevation differences of over 3,000 m and distances of ice-free areas from the coast up to 650 km inland create sharp contrasts in climatic conditions and have a marked impact on pedogenesis. Permafrost is continuous in MacRobertson Land. Active-layer depths range from 25 cm in the Grove Mountains to 110 cm or more on the coast. Patterned ground is ubiquitous in the areas with frost-susceptible parent materials throughout the region. Soil-forming processes can be examined along an elevational-longitudinal gradient from the Vestfold-Larsemann Hills to the southern Prince Charles and Grove Mountains. Salinization, manifested in salt efflorescence, carbonation, and permafrost development are expected to increase from the coast inland; pervection, and soil organic matter accumulation are greatest along the coast. Desert pavement formation and rubification are important processes along the entire gradient. Unlike Wilkes Land and South Shetland Islands, podzolization has not been reported in MacRobertson Land. The dominant soil taxa along the coast are Aquiturbels, Haploturbels, previously unclassified ornithogenic and limnogenic soils, and endo- and epi-lithic soil-like bodies. Lithic Anhyorthels are predominant in the inland mountains.

Alteration of rocks by endolithic organisms is one of the pathways for the beginning of soils on Earth

Subaerial endolithic systems of the current extreme environments on Earth provide exclusive insight into emergence and development of soils in the Precambrian when due to various stresses on the surfaces of hard rocks the cryptic niches inside them were much more plausible habitats for organisms than epilithic ones. Using an actualistic approach we demonstrate that transformation of silicate rocks by endolithic organisms is one of the possible pathways for the beginning of soils on Earth. This process led to the formation of soil-like bodies on rocks in situ and contributed to the raise of complexity in subaerial geosystems. Endolithic systems of East Antarctica lack the noise from vascular plants and are among the best available natural models to explore organo-mineral interactions of a very old “phylogenetic age” (cyanobacteria-to-mineral, fungi-to-mineral, lichen-to-mineral). On the basis of our case study from East Antarctica we demonstrate that relatively simple endolithic systems of microbial and/or cryptogamic origin that exist and replicate on Earth over geological time scales employ the principles of organic matter stabilization strikingly similar to those known for modern full-scale soils of various climates.

Microbial biomass and biological activity of soils and soil-like bodies in coastal oases of Antarctica

The method of luminescent microscopy has been applied to study the structure of the microbial biomass of soils and soil-like bodies in East (the Thala Hills and Larsemann Hills oases) and West (Cape Burks, Hobbs coast) Antarctica. According to Soil Taxonomy, the studied soils mainly belong to the subgroups of Aquic Haploturbels, Typic Haploturbels, Typic Haplorthels, and Lithic Haplorthels. The major contribution to their microbial biomass belongs to fungi. The highest fungal biomass (up to 790 μg C/g soil) has been found in the soils with surface organic horizons in the form of thin moss/lichen litters, in which the development of fungal mycelium is most active. A larger part of fungal biomass (70–98%) is represented by spores. For the soils without vegetation cover, the accumulation of bacterial and fungal biomass takes place in the horizons under surface desert pavements. In the upper parts of the soils without vegetation cover and in the organic soil horizons, the major part (>60%) of fungal mycelium contains protective melanin pigments. Among bacteria, the high portion (up to 50%) of small filtering forms is observed. A considerable increase (up to 290.2 ± 27 μg C/g soil) in the fungal biomass owing to the development of yeasts has been shown for gley soils (gleyzems) developing from sapropel sediments under subaquatic conditions and for the algal–bacterial mat on the bottom of the lake (920.7 ± 46 μg C/g soil). The production of carbon dioxide by the soils varies from 0.47 to 2.34 μg C–CO2/(g day). The intensity of nitrogen fixation in the studied samples is generally low: from 0.08 to 55.85 ng С2Н4/(g day). The intensity of denitrification varies from 0.09 to 19.28 μg N–N2O/(g day).

Soil-like bodies on Mars

Soils sensu stricto are absent on Mars; most probably, they have never been formed there, because, up to now, we have no evidence of the presence of life, either relict or recent, on this planet. Numerous references to “Martian soils” in scientific literature concern loose substrates rather than Dokuchaev’s soils. In this context, surface bodies on Mars can be described using the concept of planetary shells, or exons. Exons can be subdivided into sitons formed via in situ transformation of parent material, transons formed in the course of lateral transportation and deposition of substances, and transsitons formed by the combination of both in situ and lateral processes. Among Martian exons, transons predominate. They represent loose sediments of mainly eolian genesis related to extremely strong winds. Soil-like bodies (soloids) on Mars are represented by sitons and transsitons. These are abiotic formations having the profiles differentiated by the contents of iron oxides, soluble salts, and clay minerals and mainly formed in the presence of liquid water during the paleohumid eras of Mars evolution more than 2.5/3 billion years ago. True deep sitons (Martian weathering mantles) could only be formed under the impact of long-term weathering on stable surfaces during humid eras. Then, they were either buried by later deposited sediments, or eroded. Up to now, such objects have not been discovered on Mars.