Permafrost-A ff ected Soils of the Russian Arctic and their Carbon Pools

Introduction Conclusions References


Introduction
In wide areas of the high latitudes of Northern Europe, Greenland, Canada, Alaska and Russia, a particular group of soils has developed during the Quaternary whose diversity is based primarily on special cryopedogenetic processes within the pedosphere of our Earth system.Among the most important cryopedogenetic processes are the Figures

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Full cryogenic weathering (frost wedging), ice segregation and accumulation (by increased freezing on of water on existing ice lenses), cryoturbation (mixing of soils by repeated freezing and thaw and, consequently, expansion and contraction processes), cryometamorphosis (transformation of soil structures due to ice), gelifluction (slow, wide-area downflow of soil material of the seasonally thawed layer on slopes with an inclination of > 2 • ), frost heave, frost sorting (material dislocation caused by the increase in volume during the freezing of water) and frost crack formation (due to the contraction of the frozen soil at very low temperatures) (Fig. 1).
The areas of the Northern Hemisphere covered by permafrost extend over almost 23 million km 2 , approximately one quarter of their total land surface (Baranov, 1959;Shi, 1988;Zhang, 1999Zhang, , 2003;;French, 2007).They are called permafrost areas if their subsurface soils and sediments maintain temperatures of 0 • C or below during two consecutive years (van Everdingen, 2005) (see Fig. 2a).Under this definition, the ground water -if it contains many dissolved substances or is hold in fine pores -can also exist in liquid form in permafrost.In order to unambiguously demarcate permafrost from the supra permafrost above it, the term cryotic (temperature < 0 • C) was introduced (French, 2007).In addition to this point of view, which focuses on the ground temperature regime and designates the boundary of the ground that is permanently below 0 • C as the so-called permafrost table, there is another point of view that focuses on the thaw-freeze cycle.This distinguishes, in the upper ground area, the seasonal thaw layer from the underlying permanently frozen ground (Fig. 2b).
A spatial differentiation of the permafrost areas is based on the portion of the areas on top of the permafrost in relation to the total surface of an area in continuous, discontinuous, and sporadic and isolated permafrost.In addition to the high latitudes of the Northern Hemisphere, permafrost and permafrost-affected soils are also found in the mountains of the earth and the ice-free areas of Antarctica; there, however, only in small portions of the surface (0.35 % of Antarctica) (Bockheim, 1995;Vieira et al., 2010).The Antarctic permafrost-affected soils represent special, extremely cold and salt-rich habitats (Bockheim, 1979(Bockheim, , 2002;;Bockheim and McLeod, 2008) The extension of the terrestrial permafrost areas does not entirely correspond to the extension of the permafrost-affected soils.These soils form their own class or reference group of the highest category in the various international soil systematics.
In current use are primarily the American classification system "Keys to Soil Taxonomy" (Soil Survey Staff, 2010) with the so-called Gelisols (from Latin gelus = ice) as permafrost-affected soil class (Fig. 3 and Fig. 4), and the international reference system of the "WRB: World Reference Base for Soil Resources" of the international Food and Agriculture Organization (FAO, 2007) with the Cryosol group (cryos = cold).The diagnostic horizons, or characteristics, of these soils are the existence of permafrost in the uppermost meter of the soil, or clear cryoturbation characteristics and/or segregation ice (gelic material according to US Soil Taxonomy (Soil Survey Staff, 2010)) in the active layer of the soil above the permafrost present within a depth of 2 m (Fig. 2 and Fig. 4).An advantage of using both of these systems is the easy comparability of the various national and international studies on permafrost-affected soils.
In the Russian classification systems, permafrost-affected soils with cryoturbation and cryometamorphosis, widespread in Russian Federation, are treated as Cryozems in a separate soil class.All other soils of these areas without these two characteristics are allocated to other soil classes with the additional mention of the subjacent permafrost (such as alluvisol with underlying permafrost (Shishov et al., 2004)).Alternatively, permafrost is included as a state of soils and their specifications (Elovskaya, 1987).In Germany, permafrost-affected soils only exist as relictic or fossil remnants of periglacial soil formations.In the current German soil classification (AG Boden, 2005), they are not described independently, but can be counted as paleo soils (such as recent podzol on top of cryoturbated nonsorted circles).Remnants of these soils are occasionally described in connection with the periglacial layers (AG Boden, 2005;Altermann et al., 2008).
The spatial extension of the gelisols or cryosols north of the fiftieth degree latitude covers 27 % of the land mass (Jones et al., 2010) and corresponds to approx.8.6 million km 2 .The permafrost-affected soils (here cryosols according to the WRB, FAO, Introduction

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The properties and the spatial distribution of the permafrost-affected soils within the various countries were collected by Tarnocai (2004) und Smith and Veldhuis (2004) for Canada, by Ping et al. (2004a) for Alaska, by Goryachkin and Ignatenko (2004), Naumov (2004), Karavaeva (2004), Sokolov et al. (2004) and Gracheva (2004) for the diverse and extensive areas of Russia, by Maximovich (2004) for Mongolia and by Ping et al. (2004b) for China and published as a book titled "Cryosols Permafrost-Affected Soils" by Kimble (2004).The book contains a comprehensive description of the research into permafrost-affected soils and their history, as well as the spatial distribution of these soils along with their properties.It not only addresses the discussion of the various national and international classification systems, but also the potential uses as settlement areas, agricultural land, and as supplier of natural resources."Permafrost Soils" by Margesin (2009) is a comprehensive book focusing on the biology of permafrost-affected soils.Aspects such as biodiversity and bioactivity (e.g.Ozerskaya et al., 2009;Panikov, 2009), the effect of global warming (e.g.Wagner and Liebner, 2009) and the problems of pollutant accumulation in permafrost area (e.g.Barnes and Chuvilin, 2009) are covered in this book.

Permafrost-affected soils as carbon stores
The low average temperatures and the extreme annual temperature differences in the permafrost areas have led to a considerable accumulation of organic matter in the Quaternary.The biomass, newly formed during the short summer phase, is initially accumulated after die-off in the uppermost active layer of the soil.The annually recurring accumulation of organic matter -and often also fluvial or aeolian sedimentation of mineral matter -can lead to an upward shift of the soil surface as well as of the surface of the permanently frozen ground, so that gradually more and more organic matter is Introduction

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Full incorporated.Cryoturbation also leads to the inclusion of organic matter in deeper soil horizons.Another process is the relocation of organic matter in dissolved state and its precipitation and deposition above the permafrost table, where it was able to accumulate over millennia due to the very low temperatures and low decay rates.The permafrost-affected soils, therefore, are relevant carbon sinks, which are effective over long periods of time (Post et al., 1982;Corradi et al., 2005;Kutzbach et al., 2007;van der Molen et al., 2007;McGuire et al., 2009).The sink function occurred primarily via the soils near the surface, which incorporate the biomass of the typical arctic climateadapted tundra vegetation after its die-off as litter in their carbon sink.According to current estimates, 1024 Pg of organic carbon are stored in permafrost-affected soils down to a depth of 3 m (Tarnocai et al., 2009).Adding the deep-reaching sediments rich in organic carbon of the Yedoma landscapes and arctic deltas, the total estimates of the organic carbon stored in permafrost areas amount to about 1670 Pg (Tarnocai et al., 2009).These estimates were based on the Northern Circumpolar Soil Carbon Database (NCSCD, Tarnocai et al., 2007), the most comprehensive currently available database on organic carbon in permafrost-affected soils, which currently is being updated (Hugelius et al., 2013a, b).However, even the information in this database is still fraught with great uncertainties at the present time.When looking closely at the distribution of the sites considered so far, it becomes apparent that when evaluating the reliability of the soil data stored in the database (100 % = "reliable," 0 % = "unreliable," according to Kuhry et al., 2010), the arctic delta areas and the Yedoma landscapes with ice-rich permafrost sediments in Siberia (Fig. 6), based on the very sketchy and difficult-to-access data situation regarding permafrost-affected soils of this region until now, can only be assessed with a reliability of less than 33 %.The areas of the North American region, on the other hand, are very well represented with up to 80 % (Kuhry et al., 2010).This can be attributed to the above-average number of published soil studies in these regions.In publications of recent years, some ambiguities were apparent in the estimates of the carbon quantities stored in the permafrost-affected soils.These stemmed, on the one hand, from the unbalanced distribution of existing soil study data, Introduction

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Full and on the other hand, the widely varying definitions of the respective research objects.The number of publications on carbon contents in permafrost-affected soils is manageable (Table 1).Using the two most-cited publications, Post et al. (1982) and Tarnocai et al. (2009), as examples, these different points of view are easily illustrated: while Post et al. (1982), in the course of a global determination of the carbon pools of all lifezones, only consider 48 soil profiles in arctic tundra areas to a depth of 100 cm, Tarnocai et al. (2009) combined and updated the pedological results of existing studies from permafrost regions (e.g.Zimov et al., 2006;Schuur et al., 2008) and supplemented them with their own data.More than 400 soil profiles were evaluated, and the pool of organic carbon for various studies objects such as the permafrost-affected soils to a depth of 3 m, the arctic delta areas (up to 50 m depth) or the Yedoma landscapes (up to 25 m depth) were calculated.
Looking at the results compiled in Table 1, one will notice that the study results can be divided into two main groups: the results to a depth of 30 cm and those to 100 cm.Another group comprises carbon studies that limit their sampling to the active layer that is further defined (depths of 20 cm up to 50 cm) or only to certain soil horizons.All study results show that the permafrost-affected soils store a large quantity of carbon per soil surface.The carbon pool fluctuates between 4 kg m −2 and 25 kg m −2 for the upper 30 cm of the soils.When the authors inspected variously defined depths of the thaw soils on the day of sampling, the carbon pool lay between 13 kg m −2 and 29 kg m −2 .
The results of the studies that examined the carbon pool up to a depth of 100 cm vary between 4 kg m −2 and 71 kg m −2 (Table 1).Furthermore, these data reveal the very high fluctuation range of the results from different permafrost regions.
Observing the data of current literature on total mass of organic carbon in the permafrost areas (Table 1), the problematic aspect of comparability becomes obvious.The results of the studies refer to very different surfaces in terms of size.The studied surfaces may be countries, regions or even vegetation units.Despite the difficult comparability, the results of these studies illustrate that the total pool of the permafrost-affected soils' organic carbon is very high at 1024 Pg (Tarnocai et al., 2009)

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Full  , 2007), respectively.The carbon quantities stored in permafrostaffected soils are therefore to be considered one of the most important factors for the understanding and function of the cryosphere within the climate system.Permafrostaffected soils with their special carbon dynamics are very sensitive to environmental and climatic changes due to their temperature dependence.It can be assumed -for the past as well as for the present -that global and regional environmental and climatic changes, as well as the dynamics of soil carbon in permafrost areas interact and will continue to interact with one another via physical and biogeochemical feedback mechanisms (McGuire et al., 2009;Grosse et al., 2011).With the currently predicted climate warming and its particularly strong effects in the arctic regions (Lembke et al., 2007), and the concurrent local and regional decline and degradation of permafrost (Anisimov and Nelson, 1997), the properties of permafrost-affected soils will undergo a fundamental change.
Warming within the permafrost areas can lead to an augmentation of the thickness of the seasonally thawed layer in the upper soil (Fig. 2) and to a change in its hydrological site conditions (Koven et al., 2011).This leads to an increased microbial decay of the organic matter and a more intensive release of the climate-relevant trace gases carbon dioxide, methane and nitrogen oxide (Dutta et al., 2006;Wagner et al., 2007;Khvorostyanov et al., 2008;Schuur et al., 2009;Lee et al., 2012;Knoblauch et al., 2013).
In other words, if the current warming of the arctic climate is the cause of an increased decline in the extent of the permafrost areas, which in turn leads to an increased release of greenhouse gases in the Earth's atmosphere, a further rise in temperatures on a global scale, but also in the permafrost areas themselves must be expected (Fig. 7).
These processes show the positive feedback effects in permafrost landscapes or in the cryosphere of our Earth system that are not yet sufficiently considered in the climate models relating to temperature projection.Because of these complex effects, the Introduction

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Full permafrost areas in particular represent an important possible tipping element of the global climate system, relevant even for politics and society (Lenton and Schellnhuber, 2010).A tipping element is considered to consist of those components of the Earth system that can essentially and irrevocably be altered under loads beyond critical limits (Lenton and Schellnhuber, 2010).Whether the soils of the permafrost areas already act as carbon sources (Oechel et al., 1993(Oechel et al., , 2000;;Zimov et al., 1997) or still accumulate carbon (Corradi et al., 2005;Kutzbach et al., 2007;van der Molen et al., 2007;Hayes et al., 2011) is not yet clear and has to be assessed differently on a regional scale.The complexity of these carbon source/sink functions of the permafrost-affected soils is not yet sufficiently understood.There is a lack of measurements, as well as robust, adequately validated modelled projections and predictions to make reliable prognoses for the development of the carbon dynamics of permafrost-affected soils in the warming climate system (McGuire et al., 2009).

Current level of knowledge of the carbon pool in permafrost-affected soils in Russian Arctic
Because of the particular relevance of the cryosphere and especially the terrestrial permafrost for climate system research, the number of published scientific articles focusing on carbon in the permafrost regions has dramatically increased during the past five years compared to the last 20 years (Fig. 8).
The largest part of these published articles deals with the North American region.
In recent years however, areas of the Eurasian permafrost -especially in the Russian region -have also been increasingly studied in detail.The data of these small research areas can only be used reliably so far for local upscaling of the carbon quantities.Special permafrost phenomena such as ice and organic-rich sediments of the Yedoma landscapes, which have until now been largely neglected, were increasingly being studied (Zimov et al., 2006;Schirrmeister et al., 2011;Strauss et al., 2013).Introduction

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The turnover of organic matter in the soil and the associated formation of greenhouse gases in moist tundra areas of Eurasia were also researched on a small scale as part of field campaigns (e.g.Wüthrich et al., 1999;Rivkina et al., 2007;Knoblauch et al., 2008Knoblauch et al., , 2013;;Wagner et al., 2009;Liebner et al., 2011;Shcherbakova et al., 2011).
First English-language works on the survey of the carbon quantities in the permafrost-affected soils of the Siberian Arctic also exist (Gundelwein et al., 2007;Introduction Conclusions References Tables Figures

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Full Zubrzycki et al., 2012a;Zubrzycki et al., 2013).Their results determined for small areas of Siberia are comparable to those of other areas (see Table 1).It also becomes apparent, however, that inaccuracies can occur in global extrapolations if the data situation from the individual regions is insufficient (Zubrzycki et al., 2012a).The carbon pools are not only recorded in the Siberian Arctic, but also in the European-Russian Arctic by means of field work, and extrapolated onto larger areas via remote sensing methods (Mazhitova et al., 2003;Hugelius and Kuhry, 2009;Hugelius et al., 2011).In addition to the above studies limited to 1 m through 3 m of the carbon pools in the permafrost-affected soils, the study of special permafrost phenomena such as the sediments of the Yedoma landscapes is important.The studies of Siberian regions show that these sediments have high gravimetric carbon content, which however, is subject to strong fluctuations depending on the studied site.It is usually between 1 %wt and 4 %wt, but can also reach values of up to 17 %wt in the case of peaty layers (Zimov et al., 1997(Zimov et al., , 2006;;Schirrmeister et al., 2011;Strauss et al., 2013).

Research requirements
A significant number of new data records on soils and the quantities of carbon stored in them from the under-represented areas of the circumpolar regions -especially the Siberian Arctic -is necessary to update the Northern Circumpolar Soil Carbon Database (Tarnocai et al., 2009;Kuhry et al., 2010;Hugelius et al., 2013a, b).This can only be achieved by combining measuring fieldwork with modelling work for the permafrost areas, primarily for the Eurasian and especially for the Siberian region.Because of the sketchy data situation, special focus should be directed not only to the delta deposits, the ice-rich sediments of the Yedoma landscapes (see Tarnocai et al., 2009), but also to the permafrost-affected soils of the hilly and mountainous regions.The more comprehensive data basis is necessary for a better understanding of the interactions between the particular climate, soil and vegetation conditions in the permafrost areas.From this information, a drawing of conclusions will be enabled re-Introduction

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Full garding the factors of the processes occurring today or the future remobilization of the labile organic carbon of the permafrost-affected soils.For future research projects, it is important to reach high interdisciplinarity among the researchers in one area, because only the synthesis of the various research approaches and their results can lead to an improved understanding of the permafrost-affected soils and their carbon dynamics.
Since not only the size of the carbon pool in permafrost-affected soils varies regionally (McGuire et al., 2009), its recent carbon source and sink function is also different from region to region.In addition, since field research cannot be carried out everywhere with sufficient intensity, large-scale thematic soil-type maps should initially be drawn up on a regional basis.These results, gathered from fieldwork and shown in maps, may serve as the basis for future extrapolations of various element fluxes.With the help of high-resolution vegetation and soil-type maps of underrepresented areas containing soil texture and hydrology, more accurate estimates of the carbon pool of the circumpolar permafrost region can be performed using GIS-analyses (compare to Hugelius, 2012;Pastukhov and Kaverin, 2013;Zubrzycki et al., 2013).To this end, many already existing soil and sediment samples could be reanalyzed.Afterwards, new work areas can be targeted to fill the research gaps.
Data on the carbon pools and processes in the permafrost areas, obtained via targeted field and lab work, can be integrated into new and more reliable models.Through the synergistic and interdisciplinary collaboration of measurement and modelling permafrost researchers, it will be possible to model the development of these vast areas with their enormous quantities of potentially labile organic carbon and facilitate prognoses regarding possible greenhouse gas emissions from permafrost-affected soils.These, in turn, will lead to new, more realistic future projections of global temperature development and reduce the current uncertainty surrounding the significance of the cryosphere, including the carbon pools in permafrost-affected soils, for the climate system.Introduction

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Full

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Full  1. Overview of carbon studies from different permafrost regions.Only results related to the permafrost-affected soils are presented.This list shows only some examples and is not intended to be exhaustive.SOC = soil organic carbon.Tarnocai and Smith (1992) 4.0 63.0 Canada Desyatkin et al. (1994) 16.0 Yakutian tundra Matsuura and Yefremov (1995) 11.0 20.0 Russia Kolchugina et al. (1995) 21.4 Russian tundra soils Rozhkov et al. (1996) 116 Tundra and northern Taiga in Russia Ping et al. (1997) 31.4 69.2 Tundra in Alaska Chestnyck et al. (1999) 17.8 East European Russian tundra Stolbovoi (2002) 16.6 26.9 107 Russia Tarnocai et al. (2003) 25 Full Examples are gleying properties (suffix "g") described as formation of grey, greenish and bluish spots caused by reduced iron.Iron reduction occurs when soils are water-saturated for long periods.In this case, the soil parent material consists of fluvial sands that were deposited during a flood in the study area.Suffixes "i", "e" and "a" classify the O horizon's organic matter in "slightly", intermediately" and "highly" decomposed.The existence of iron and/or manganese concretions is indicated by suffix "c".Introduction Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | mass of carbon of the entire global vegetation biomass or the atmosphere of 650 Pg and 750 Pg (IPCC Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | previously printed manuscript (Zubrzycki, S., Kutzbach, L. and Pfeiffer, E.-M.: Böden in Permafrostgebieten der Arktis als Kohlenstoffsenke und Kohlenstoffquelle.Polarforschung 81(1): 33-46, 2012).We thank Darren R. Gröcke, the Chief-Executive Editor of Solid Earth, for giving an opportunity to broader the audience by accepting the submission of the new English-written version of our manuscript.Discussion Paper | Discussion Paper | Discussion Paper | Grosse, G., Harden, J., Turetsky, M., McGuire, A. D., Camill, P., Tarnocai, C., Frolking, S., Schuur, E. A. G., Jorgenson, T., Marchenko, S., Romanovsky, V., Wickland, K. P., French, N., Waldrop, M., Bourgeau-Chavez, L., and Striegl, R. G.: Vulnerability of high-latitude soil organic carbon in North America to disturbance, J. Geophys.Res.-Biogeo., 116, G00K06, doi:10.1029/2010JG001507,2011Discussion Paper | Discussion Paper | Discussion Paper | storage to 3 m depth in soils of the northern circumpolar permafrost region, Earth Syst.Sci.Data Discuss., 6, 73-93, doi:10.5194/essdd-6-73-2013,2013b.IPCC -Intergovernmental Panel on Climate Change: Climate Change 2007 -IPCC Fourth Assessment Report.Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007.