S. V. Goryachkin

Vulnerability of permafrost carbon to climate change: Implications for the global carbon cycle

ABSTRACT Thawing permafrost and the resulting microbial decomposition of previously frozen organic carbon (C) is one of the most significant potential feedbacks from terrestrial ecosystems to the atmosphere in a changing climate. In this article we present an overview of the global permafrost C pool and of the processes that might transfer this C into the atmosphere, as well as the associated ecosystem changes that occur with thawing. We show that accounting for C stored deep in the permafrost more than doubles previous high-latitude inventory estimates, with this new estimate equivalent to twice the atmospheric C pool. The thawing of permafrost with warming occurs both gradually and catastrophically, exposing organic C to microbial decomposition. Other aspects of ecosystem dynamics can be altered by climate change along with thawing permafrost, such as growing season length, plant growth rates and species composition, and ecosystem energy exchange. However, these processes do not appear to be able to compensate for C release from thawing permafrost, making it likely that the net effect of widespread permafrost thawing will be a positive feedback to a warming climate.

Dynamics of carbon pools in post-agrogenic sandy soils of southern taiga of Russia

BackgroundUntil recently, a lot of arable lands were abandoned in many countries of the world and, especially, in Russia, where about half a million square kilometers of arable lands were abandoned in 1961-2007. The soils at these fallows undergo a process of natural restoration (or self-restoration) that changes the balance of soil organic matter (SOM) supply and mineralization.ResultsA soil chronosequence study, covering the ecosystems of 3, 20, 55, 100, and 170 years of self-restoration in southern taiga zone, shows that soil organic content of mineral horizons remains relatively stable during the self-restoration. This does not imply, however, that SOM pools remain steady. The C/N ratio of active SOM reached steady state after 55 years, and increased doubly (from 12.5 - 15.6 to 32.2-33.8). As to the C/N ratio of passive SOM, it has been continuously increasing (from 11.8-12.7 to 19.0-22.8) over the 170 years, and did not reach a steady condition.ConclusionThe results of the study imply that soil recovery at the abandoned arable sandy lands of taiga is incredibly slow process. Not only soil morphological features of a former ploughing remained detectable but also the balance of soil organic matter input and mineralization remained unsteady after 170 years of self-restoration.

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.

Similarities and Differences in Arctic and Antarctic Soil Zones

Soil scientists developed basic concepts of the geography of Arctic and Antarctic soils about 20 years ago (Tedrow, 1977; Karavaeva, Targulian, 1977; Sokolov et al., 1982). They acquired abundant information on soils and soil-forming factors, studied the soils of the Antarctic circumpolar region in detail, and suggested zonal patterns for the region (Campbell, Claridge, 1987; Bockheim, Ugolini, 1990; Blume et al., 1997). Their findings contain many discrepancies, however, and they demand reinterpretation of the spatial distribution of soils at high latitudes of the Northern Hemisphere and comparative analysis of soil covers of the Arctic and Antarctic.

Global climate changes and the soil cover

The relationships between climate changes and the soil cover are analyzed. The greenhouse effect induced by the rising concentrations of CO2, CH4, N2O, and many other trace gases in the air has been one of the main factors of the global climate warming in the past 30–40 years. The response of soils to climate changes is considered by the example of factual data on soil evolution in the dry steppe zone of Russia. Probable changes in the carbon cycle under the impact of rising CO2 concentrations are discussed. It is argued that this rise may have an effect of an atmospheric fertilizer and lead to a higher productivity of vegetation, additional input of organic residues into the soils, and activation of soil microflora. Soil temperature and water regimes, composition of soil gases, soil biotic parameters, and other dynamic soil characteristics are most sensitive to climate changes. For the territory of Russia, in which permafrost occupies more than 50% of the territory, the response of this highly sensitive natural phenomenon to climate changes is particularly important. Long-term data on soil temperatures at a depth of 40 cm are analyzed for four large regions of Russia. In all of them, except for the eastern sector of Russian Arctic, a stable trend toward the rise in the mean annual soil temperature. In the eastern sector (the Verkhoyansk weather station), the soil temperature remains stable.

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.

Soil formation and weathering on ultramafic rocks in the mountainous tundra of the Rai-Iz massif, Polar Urals

Gravelly clay loamy and clayey soils developed from the derivatives of ultramafic rocks of the dunite-harzburgite complex of the Rai-Iz massif in the Polar Urals have been studied. They are represented by raw-humus pelozems (weakly developed clayey soils) under conditions of perfect drainage on steep slopes and by the gleyzems (Gleysols) with vivid gley color patterns in the eluvial positions on leveled elements of the relief. The magnesium released from the silicates with the high content of this element (mainly from olivine) specifies the neutral-alkaline reaction in these soils. Cryoturbation, the accumulation of raw humus, the impregnation of the soil mass with humic substances, gleyzation, and the ferrugination of the gleyed horizons are also clearly pronounced in the studied soils. Despite the high pH values, the destruction of supergene smectites in the upper horizons and ferrugination (the accumulation of iron hydroxides) in the microfissures dissecting the grains of olivine, pyroxene, and serpentine, and in decomposing plant tissues take place. The development of these processes may be related to the local acidification (neutralization) of the soil medium under the impact of biota and carbonic acids. The specificity of gleyzation in the soils developing from ultramafic rocks is shown in the absence of iron depletion from the fine earth material against the background of the greenish blue gley color pattern.

Distribution of rare-earth (Y, La, Ce) and other heavy metals in the profiles of the podzolic soil group

Along with Fe and Al, many heavy metals (Mn, Cr, Zn, Cu, and Ni) show a markedly pronounced eluvial-illuvial redistribution in the profiles of soils of the podzolic group. The intensity of the redistribution of the bulk forms of these metals is comparable with that of Fe and exceeds that of Al. Although the podzolic soils are depleted of rare-earth metals, the latter respond readily to soil podzolization. The inactive participation of Al is explained by an insignificant portion of the active reaction-capable fraction. Podzolization does not influence the profile distribution of Sr and Ba. The leaching degree of heavy metals such as Mn, Cr, Zn, Ni, and Zr is noticeably higher in the sandy podzols than in the loamy podzolic soils. Leaching of heavy metals from the podzolic horizons is of geochemical importance, whereas the depletion of metals participating in plant nutrition and biota development is of ecological importance. The leaching of heavy metals is related to the destruction of clay particles in the heavy-textured podzolic soils; the effect of the soil acidity on the leaching of heavy metals is less significant.

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.

Changes in soil respiration in the course of the postagrogenic succession on sandy soils in the southern taiga zone

The dynamics of the CO2 emission from sandy soils in the course of the postagrogenic succession in the southern taiga zone were studied. We measured total emission from the soil surface and, separately, respiration from the litter and mineral soil horizons during the warm (snowless) seasons of 2010 and 2011 on differently aged fallow plots: 0 years (cropland) and 7, 23, 55, 100, and 170 years. It was demonstrated that changes in the CO2 emission in the course of the succession have a nonlinear pattern: the emission sharply increases in the first decade, then somewhat decreases, and then gradually increases again up to the maximum values. This is explained by the dependence of the rate of the emission on the soil carbon pools (humus + litter + underground phytomass) that are also subjected to nonlinear changes. Initially, the emission is mainly due to mineralization of labile organic substances added to the plowed soils in the form of organic fertilizers. Then, in parallel with a gradual increase in the pools of litter and underground phytomass, the total pool of soil organic carbon increases, and its role in the emission becomes more pronounced. The seasonal dynamics of the soil respiration are mainly controlled by the soil temperature; the soil moistening plays an important role only during the initial meadow stage of the succession.