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  • 1. Abbott, Benjamin W.
    et al.
    Jones, Jeremy B.
    Schuur, Edward A. G.
    Chapin, F. Stuart
    Bowden, William B.
    Bret-Harte, M. Syndonia
    Epstein, Howard E.
    Flannigan, Michael D.
    Harms, Tamara K.
    Hollingsworth, Teresa N.
    Mack, Michelle C.
    McGuire, A. David
    Natali, Susan M.
    Rocha, Adrian V.
    Tank, Suzanne E.
    Turetsky, Merritt R.
    Vonk, Jorien E.
    Wickland, Kimberly P.
    Aiken, George R.
    Alexander, Heather D.
    Amon, Rainer M. W.
    Benscoter, Brian W.
    Bergeron, Yves
    Bishop, Kevin
    Blarquez, Olivier
    Bond-Lamberty, Ben
    Breen, Amy L.
    Buffam, Ishi
    Cai, Yihua
    Carcaillet, Christopher
    Carey, Sean K.
    Chen, Jing M.
    Chen, Han Y. H.
    Christensen, Torben R.
    Cooper, Lee W.
    Cornelissen, J. Hans C.
    de Groot, William J.
    DeLuca, Thomas H.
    Dorrepaal, Ellen
    Fetcher, Ned
    Finlay, Jacques C.
    Forbes, Bruce C.
    French, Nancy H. F.
    Gauthier, Sylvie
    Girardin, Martin P.
    Goetz, Scott J.
    Goldammer, Johann G.
    Gough, Laura
    Grogan, Paul
    Guo, Laodong
    Higuera, Philip E.
    Hinzman, Larry
    Hu, Feng Sheng
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jafarov, Elchin E.
    Jandt, Randi
    Johnstone, Jill F.
    Karlsson, Jan
    Kasischke, Eric S.
    Kattner, Gerhard
    Kelly, Ryan
    Keuper, Frida
    Kling, George W.
    Kortelainen, Pirkko
    Kouki, Jari
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Laudon, Hjalmar
    Laurion, Isabelle
    Macdonald, Robie W.
    Mann, Paul J.
    Martikainen, Pertti J.
    McClelland, James W.
    Molau, Ulf
    Oberbauer, Steven F.
    Olefeldt, David
    Pare, David
    Parisien, Marc-Andre
    Payette, Serge
    Peng, Changhui
    Pokrovsky, Oleg S.
    Rastetter, Edward B.
    Raymond, Peter A.
    Raynolds, Martha K.
    Rein, Guillermo
    Reynolds, James F.
    Robards, Martin
    Rogers, Brendan M.
    Schaedel, Christina
    Schaefer, Kevin
    Schmidt, Inger K.
    Shvidenko, Anatoly
    Sky, Jasper
    Spencer, Robert G. M.
    Starr, Gregory
    Striegl, Robert G.
    Teisserenc, Roman
    Tranvik, Lars J.
    Virtanen, Tarmo
    Welker, Jeffrey M.
    Zimov, Sergei
    Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment2016In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, no 3, article id 034014Article in journal (Refereed)
    Abstract [en]

    As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

  • 2. Alfredsson, H.
    et al.
    Clymans, W.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Conley, D. J.
    Estimated storage of amorphous silica in soils of the circum-Arctic tundra region2016In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 30, no 3, p. 479-500Article in journal (Refereed)
    Abstract [en]

    We investigated the vertical distribution, storage, landscape partitioning, and spatial variability of soil amorphous silica (ASi) at four different sites underlain by continuous permafrost and representative of mountainous and lowland tundra, in the circum-Arctic region. Based on a larger set of data, we present the first estimate of the ASi soil reservoir (0-1m depth) in circum-Arctic tundra terrain. At all sites, the vertical distribution of ASi concentrations followed the pattern of either (1) declining concentrations with depth (most common) or (2) increasing/maximum concentrations with depth. Our results suggest that a set of processes, including biological control, solifluction and other slope processes, cryoturbation, and formation of inorganic precipitates influence vertical distributions of ASi in permafrost terrain, with the capacity to retain stored ASi on millennial timescales. At the four study sites, areal ASi storage (0-1m) is generally higher in graminoid tundra compared to wetlands. Our circum-Arctic upscaling estimates, based on both vegetation and soil classification separately, suggest a storage amounting to 219 +/- 28 and 274 +/- 33 Tmol Si, respectively, of which at least 30% is stored in permafrost. This estimate would account for about 3% of the global soil ASi storage while occupying an equal portion of the global land area. This result does not support the hypothesis that the circum-Arctic tundra soil ASi reservoir contains relatively higher amounts of ASi than other biomes globally as demonstrated for carbon. Nevertheless, climate warming has the potential to significantly alter ASi storage and terrestrial Si cycling in the Arctic.

  • 3. Alfredsson, Hanna
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Clymans, Wim
    Stadmark, Johanna
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Conley, Daniel J.
    Amorphous silica pools in permafrost soils of the Central Canadian Arctic and the potential impact of climate change2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 124, no 1-3, p. 441-459Article in journal (Refereed)
    Abstract [en]

    We investigated the distribution, storage and landscape partitioning of soil amorphous silica (ASi) in a central Canadian region dominated by tundra and peatlands to provide a first estimate of the amount of ASi stored in Arctic permafrost ecosystems. We hypothesize that, similar to soil organic matter, Arctic soils store large amounts of ASi which may be affected by projected climate changes and associated changes in permafrost regimes. Average soil ASi storage (top 1 m) ranged between 9600 and 83,500 kg SiO2 ha(-1) among different land-cover types. Lichen tundra contained the lowest amounts of ASi while no significant differences were found in ASi storage among other land-cover types. Clear differences were observed between ASi storage allocated into the top organic versus the mineral horizon of soils. Bog peatlands, fen peatlands and wet shrub tundra stored between 7090 and 45,400 kg SiO2 ha(-1) in the top organic horizon, while the corresponding storage in lichen tundra, moist shrub- and dry shrub tundra only amounted to 1500-1760 kg SiO2 ha(-1). Diatoms and phytoliths are important components of ASi storage in the top organic horizon of peatlands and shrub tundra systems, while it appears to be a negligible component of ASi storage in the mineral horizon of shrub tundra classes. ASi concentrations decrease with depth in the soil profile for fen peatlands and all shrub tundra classes, suggesting recycling of ASi, whereas bog peatlands appeared to act as sinks retaining stored ASi on millennial time scales. Our results provide a conceptual framework to assess the potential effects of climate change impacts on terrestrial Si cycling in the Arctic. We believe that ASi stored in peatlands are particularly sensitive to climate change, because a larger fraction of the ASi pool is stored in perennially frozen ground compared to shrub tundra systems. A likely outcome of climate warming and permafrost thaw could be mobilization of previously frozen ASi, altered soil storage of biogenically derived ASi and an increased Si flux to the Arctic Ocean.

  • 4. Bartsch, Annett
    et al.
    Widhalm, Barbara
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Siewert, Matthias Benjamin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Can C-band synthetic aperture radar be used to estimate soil organic carbon storage in tundra?2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 19, p. 5453-5470Article in journal (Refereed)
    Abstract [en]

    A new approach for the estimation of soil organic carbon (SOC) pools north of the tree line has been developed based on synthetic aperture radar (SAR; ENVISAT Advanced SAR Global Monitoring mode) data. SOC values are directly determined from backscatter values instead of upscaling using land cover or soil classes. The multi-mode capability of SAR allows application across scales. It can be shown that measurements in C band under frozen conditions represent vegetation and surface structure properties which relate to soil properties, specifically SOC. It is estimated that at least 29 Pg C is stored in the upper 30 cm of soils north of the tree line. This is approximately 25% less than stocks derived from the soil-map-based Northern Circumpolar Soil Carbon Database (NCSCD). The total stored carbon is underestimated since the established empirical relationship is not valid for peatlands or strongly cryoturbated soils. The approach does, however, provide the first spatially consistent account of soil organic carbon across the Arctic. Furthermore, it could be shown that values obtained from 1 km resolution SAR correspond to accounts based on a high spatial resolution (2 m) land cover map over a study area of about 7 x 7 km in NE Siberia. The approach can be also potentially transferred to medium-resolution C-band SAR data such as ENVISAT ASAR Wide Swath with similar to 120m resolution but it is in general limited to regions without woody vegetation. Global Monitoring-mode-derived SOC increases with unfrozen period length. This indicates the importance of this parameter for modelling of the spatial distribution of soil organic carbon storage.

  • 5. Capek, Petr
    et al.
    Diakova, Katerina
    Dickopp, Jan-Erik
    Barta, Jiri
    Wild, Birgit
    Schnecker, Jörg
    Alves, Ricardo Jorge Eloy
    Aiglsdorfer, Stefanie
    Guggenberger, Georg
    Gentsch, Norman
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lashchinsky, Nikolaj
    Gittel, Antje
    Schleper, Christa
    Mikutta, Robert
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Shibistova, Olga
    Urich, Tim
    Richter, Andreas
    Santruckova, Hana
    The effect of warming on the vulnerability of subducted organic carbon in arctic soils2015In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 90, p. 19-29Article in journal (Refereed)
    Abstract [en]

    Arctic permafrost soils contain large stocks of organic carbon (OC). Extensive cryogenic processes in these soils cause subduction of a significant part of OC-rich topsoil down into mineral soil through the process of cryoturbation. Currently, one-fourth of total permafrost OC is stored in subducted organic horizons. Predicted climate change is believed to reduce the amount of OC in permafrost soils as rising temperatures will increase decomposition of OC by soil microorganisms. To estimate the sensitivity of OC decomposition to soil temperature and oxygen levels we performed a 4-month incubation experiment in which we manipulated temperature (4-20 degrees C) and oxygen level of topsoil organic, subducted organic and mineral soil horizons. Carbon loss (C-LOSS) was monitored and its potential biotic and abiotic drivers, including concentrations of available nutrients, microbial activity, biomass and stoichiometry, and extracellular oxidative and hydrolytic enzyme pools, were measured. We found that independently of the incubation temperature, C-LOSS from subducted organic and mineral soil horizons was one to two orders of magnitude lower than in the organic topsoil horizon, both under aerobic and anaerobic conditions. This corresponds to the microbial biomass being lower by one to two orders of magnitude. We argue that enzymatic degradation of autochthonous subducted OC does not provide sufficient amounts of carbon and nutrients to sustain greater microbial biomass. The resident microbial biomass relies on allochthonous fluxes of nutrients, enzymes and carbon from the OC-rich topsoil. This results in a negative priming effect, which protects autochthonous subducted OC from decomposition at present. The vulnerability of subducted organic carbon in cryoturbated arctic soils under future climate conditions will largely depend on the amount of allochthonous carbon and nutrient fluxes from the topsoil.

  • 6. Chadburn, S. E.
    et al.
    Burke, E. J.
    Cox, P. M.
    Friedlingstein, P.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Westermann, S.
    An observation-based constraint on permafrost loss as a function of global warming2017In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 7, no 5, p. 340-344Article in journal (Refereed)
    Abstract [en]

    Permafrost, which covers 15 million km(2) of the land surface, is one of the components of the Earth system that is most sensitive to warming(1,2). Loss of permafrost would radically change high-latitude hydrology and biogeochemical cycling, and could therefore provide very significant feedbacks on climate change(3-8). The latest climate models all predict warming of high-latitude soils and thus thawing of permafrost under future climate change, but with widely varying magnitudes of permafrost thaw(9,10). Here we show that in each of the models, their present-day spatial distribution of permafrost and air temperature can be used to infer the sensitivity of permafrost to future global warming. Using the same approach for the observed permafrost distribution and air temperature, we estimate a sensitivity of permafrost area loss to global mean warming at stabilization of 4.0(-1.1)(+1.0) million km(2) degrees C-1 (1 sigma confidence), which is around 20% higher than previous studies(9). Our method facilitates an assessment for COP21 climate change targets(11): if the climate is stabilized at 2 degrees C above pre-industrial levels, we estimate that the permafrost area would eventually be reduced by over 40%. Stabilizing at 1.5 degrees C rather than 2 degrees C would save approximately 2 million km(2) of permafrost.

  • 7. Chadburn, Sarah E.
    et al.
    Krinner, Gerhard
    Porada, Philipp
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bartsch, Annett
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Belelli Marchesini, Luca
    Boike, Julia
    Ekici, Altug
    Elberling, Bo
    Friborg, Thomas
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Johansson, Margareta
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kutzbach, Lars
    Langer, Moritz
    Lund, Magnus
    Parmentier, Frans-Jan W.
    Peng, Shushi
    Van Huissteden, Ko
    Wang, Tao
    Westermann, Sebastian
    Zhu, Dan
    Burke, Eleanor J.
    Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 22, p. 5143-5169Article in journal (Refereed)
    Abstract [en]

    It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate biological and physical soil processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models. Thus, we identify three priority areas for model development: (1) dynamic vegetation including (a) climate and (b) nutrient limitation effects; (2) adding moss as a plant functional type; and an (3) improved vertical profile of soil carbon including peat processes.

  • 8. Ding, Jinzhi
    et al.
    Chen, Leiyi
    Ji, Chengjun
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Li, Yingnian
    Liu, Li
    Qin, Shuqi
    Zhang, Beibei
    Yang, Guibiao
    Li, Fei
    Fang, Kai
    Chen, Yongliang
    Peng, Yunfeng
    Zhao, Xia
    He, Honglin
    Smith, Pete
    Fang, Jingyun
    Yang, Yuanhe
    Decadal soil carbon accumulation across Tibetan permafrost regions2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 6, p. 420-424Article in journal (Refereed)
    Abstract [en]

    Permafrost soils store large amounts of carbon. Warming can result in carbon release from thawing permafrost, but it can also lead to enhanced primary production, which can increase soil carbon stocks. The balance of these fluxes determines the nature of the permafrost feedback to warming. Here we assessed decadal changes in soil organic carbon stocks in the active layer-the uppermost 30 cm-of permafrost soils across Tibetan alpine regions, based on repeated soil carbon measurements in the early 2000s and 2010s at the same sites. We observed an overall accumulation of soil organic carbon irrespective of vegetation type, with a mean rate of 28.0 g Cm-2 yr(-1) across Tibetan permafrost regions. This soil organic carbon accrual occurred only in the subsurface soil, between depths of 10 and 30 cm, mainly induced by an increase of soil organic carbon concentrations. We conclude that the upper active layer of Tibetan alpine permafrost currently represents a substantial regional soil carbon sink in a warming climate, implying that carbon losses of deeper and older permafrost carbon might be offset by increases in upper-active-layer soil organic carbon stocks, which probably results from enhanced vegetation growth.

  • 9. Faucherre, Samuel
    et al.
    Juncher Jørgensen, Christian
    Blok, Daan
    Weiss, Niels
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Siewert, Matthias Benjamin
    Stockholm University, Faculty of Science, Department of Physical Geography. Umeå University, Sweden.
    Bang-Andreasen, Toke
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Elberling, Bo
    Short and Long-Term Controls on Active Layer and Permafrost Carbon Turnover Across the Arctic2018In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 123, no 2, p. 372-390Article in journal (Refereed)
    Abstract [en]

    Decomposition of soil organic matter (SOM) in permafrost terrain and the production of greenhouse gases is a key factor for understanding climate change-carbon feedbacks. Previous studies have shown that SOM decomposition is mostly controlled by soil temperature, soil moisture, and carbon-nitrogen ratio (C:N). However, focus has generally been on site-specific processes and little is known about variations in the controls on SOM decomposition across Arctic sites. For assessing SOM decomposition, we retrieved 241 samples from 101 soil profiles across three contrasting Arctic regions and incubated them in the laboratory under aerobic conditions. We assessed soil carbon losses (C-loss) five times during a 1year incubation. The incubated material consisted of near-surface active layer (AL(NS)), subsurface active layer (AL(SS)), peat, and permafrost samples. Samples were analyzed for carbon, nitrogen, water content, C-13, N-15, and dry bulk density (DBD). While no significant differences were observed between total AL(SS) and permafrost C-loss over 1year incubation (2.32.4% and 2.51.5% C-loss, respectively), AL(NS) samples showed higher C-loss (7.94.2%). DBD was the best explanatory parameter for active layer C-loss across sites. Additionally, results of permafrost samples show that C:N ratio can be used to characterize initial C-loss between sites. This data set on the influence of abiotic parameter on microbial SOM decomposition can improve model simulations of Arctic soil CO2 production by providing representative mean values of CO2 production rates and identifying standard parameters or proxies for upscaling potential CO2 production from site to regional scales.

  • 10.
    Fuchs, Matthias
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Low below-ground organic carbon storage in a subarctic Alpine permafrost environment2015In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 9, no 2, p. 427-438Article in journal (Refereed)
    Abstract [en]

    This study investigates the soil organic carbon (SOC) storage in Tarfala Valley, northern Sweden. Field inventories, upscaled based on land cover, show that this alpine permafrost environment does not store large amounts of SOC, with an estimate mean of 0.9 +/- 0.2 kg C m(-2) for the upper meter of soil. This is 1 to 2 orders of magnitude lower than what has been reported for lowland permafrost terrain. The SOC storage varies for different land cover classes and ranges from 0.05 kg C m(-2) for stone-dominated to 8.4 kg C m(-2) for grass-dominated areas. No signs of organic matter burial through cryoturbation or slope processes were found, and radiocarbon-dated SOC is generally of recent origin (< 2000 cal yr BP). An inventory of permafrost distribution in Tarfala Valley, based on the bottom temperature of snow measurements and a logistic regression model, showed that at an altitude where permafrost is probable the SOC storage is very low. In the high-altitude permafrost zones (above 1500 m), soils store only ca. 0.1 kg C m(-2). Under future climate warming, an upward shift of vegetation zones may lead to a net ecosystem C uptake from increased biomass and soil development. As a consequence, alpine permafrost environments could act as a net carbon sink in the future, as there is no loss of older or deeper SOC from thawing permafrost.

  • 11. Gentsch, N.
    et al.
    Mikutta, R.
    Alves, R. J. E.
    Barta, J.
    Capek, P.
    Gittel, A.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lashchinskiy, N.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Richter, A.
    Santruckova, H.
    Schnecker, J.
    Shibistova, O.
    Urich, T.
    Wild, B.
    Guggenberger, G.
    Storage and transformation of organic matter fractions in cryoturbated permafrost soils across the Siberian Arctic2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, no 14, p. 4525-4542Article in journal (Refereed)
    Abstract [en]

    In permafrost soils, the temperature regime and the resulting cryogenic processes are important determinants of the storage of organic carbon (OC) and its small-scale spatial variability. For cryoturbated soils, there is a lack of research assessing pedon-scale heterogeneity in OC stocks and the transformation of functionally different organic matter (OM) fractions, such as particulate and mineral-associated OM. Therefore, pedons of 28 Turbels were sampled in 5m wide soil trenches across the Siberian Arctic to calculate OC and total nitrogen (TN) stocks based on digital profile mapping. Density fractionation of soil samples was performed to distinguish between particulate OM (light fraction, LF, < 1.6 g cm(-3)), mineral associated OM (heavy fraction, HF, > 1.6 g cm(-3)), and a mobilizable dissolved pool (mobilizable fraction, MoF). Across all investigated soil profiles, the total OC storage was 20.2 +/- 8.0 kgm(-2) (mean +/- SD) to 100 cm soil depth. Fifty-four percent of this OC was located in the horizons of the active layer (annual summer thawing layer), showing evidence of cryoturbation, and another 35% was present in the upper permafrost. The HF-OC dominated the overall OC stocks (55 %), followed by LF-OC (19% in mineral and 13% in organic horizons). During fractionation, approximately 13% of the OC was released as MoF, which likely represents a readily bioavailable OM pool. Cryogenic activity in combination with cold and wet conditions was the principle mechanism through which large OC stocks were sequestered in the subsoil (16.4 +/- 8.1 kgm(-2); all mineral B, C, and permafrost horizons). Approximately 22% of the subsoil OC stock can be attributed to LF material subducted by cryoturbation, whereas migration of soluble OM along freezing gradients appeared to be the principle source of the dominant HF (63 %) in the subsoil. Despite the unfavourable abiotic conditions, low C/N ratios and high delta C-13 values indicated substantial microbial OM transformation in the subsoil, but this was not reflected in altered LF and HF pool sizes. Partial least-squares regression analyses suggest that OC accumulates in the HF fraction due to co-precipitation with multivalent cations (Al, Fe) and association with poorly crystalline iron oxides and clay minerals. Our data show that, across all permafrost pedons, the mineral-associated OM represents the dominant OM fraction, suggesting that the HF-OC is the OM pool in permafrost soils on which changing soil conditions will have the largest impact.

  • 12. Harden, Jennifer W.
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Ahlström, Anders
    Blankinship, Joseph C.
    Bond-Lamberty, Ben
    Lawrence, Corey R.
    Loisel, Julie
    Malhotra, Avni
    Jackson, Robert B.
    Ogle, Stephen
    Phillips, Claire
    Ryals, Rebecca
    Todd-Brown, Katherine
    Vargas, Rodrigo
    Vergara, Sintana E.
    Cotrufo, M. Francesca
    Keiluweit, Marco
    Heckman, Katherine A.
    Crow, Susan E.
    Silver, Whendee L.
    DeLonge, Marcia
    Nave, Lucas E.
    Networking our science to characterize the state, vulnerabilities, and management opportunities of soil organic matter2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 2, p. e705-e718Article in journal (Refereed)
    Abstract [en]

    Soil organic matter (SOM) supports the Earth's ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon. Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use. Large land areas have lost SOC as a result of land use practices, yet there are compensatory opportunities to enhance productivity and SOC storage in degraded lands through improved management practices. Large areas with and without intentional management are also being subjected to rapid changes in climate, making many SOC stocks vulnerable to losses by decomposition or disturbance. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil-management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales. As newly engaged members of the International Soil Carbon Network, we have identified gaps in data, modeling, and communication that underscore the need for an open, shared network to frame and guide the study of SOM and SOC and their management for sustained production and climate regulation.

  • 13. Harden, Jennifer W.
    et al.
    Koven, Charles D.
    Ping, Chien-Lu
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    McGuire, A. David
    Camill, Phillip
    Jorgenson, Torre
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Michaelson, Gary J.
    O'Donnell, Jonathan A.
    Schuur, Edward A. G.
    Tarnocai, Charles
    Johnson, Kristopher
    Grosse, Guido
    Field information links permafrost carbon to physical vulnerabilities of thawing2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, p. L15704-Article in journal (Refereed)
    Abstract [en]

    Deep soil profiles containing permafrost (Gelisols) were characterized for organic carbon (C) and total nitrogen (N) stocks to 3 m depths. Using the Community Climate System Model (CCSM4) we calculate cumulative distributions of active layer thickness (ALT) under current and future climates. The difference in cumulative ALT distributions over time was multiplied by C and N contents of soil horizons in Gelisol suborders to calculate newly thawed C and N. Thawing ranged from 147 PgC with 10 PgN by 2050 (representative concentration pathway RCP scenario 4.5) to 436 PgC with 29 PgN by 2100 (RCP 8.5). Organic horizons that thaw are vulnerable to combustion, and all horizon types are vulnerable to shifts in hydrology and decomposition. The rates and extent of such losses are unknown and can be further constrained by linking field and modelling approaches. These changes have the potential for strong additional loading to our atmosphere, water resources, and ecosystems. Citation: Harden, J. W., et al. (2012), Field information links permafrost carbon to physical vulnerabilities of thawing, Geophys. Res. Lett., 39, L15704, doi: 10.1029/2012GL051958.

  • 14.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Estimating soil organic carbon storage in permafrost terrain: an evaluation of sample sizes, spatial resolution and error estimatesManuscript (preprint) (Other academic)
  • 15.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Quantity and quality of soil organic matter in permafrost terrain2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High latitude terrestrial ecosystems are considered key components in the global carbon (C) cycle and hold large reservoirs of soil organic carbon (SOC). Much of this is stored as soil organic matter (SOM) in permafrost soils and peat deposits and is vulnerable to remobilization under future global warming. While the large size and potential vulnerability of arctic SOM reservoirs is recognized, detailed knowledge on its landscape partitioning and quality is poor. This thesis describes total storage, landscape partitioning and lability of SOM stored in permafrost areas of Canada and Russia. Detailed studies of SOC partitioning highlight the importance of especially permafrost peatlands, but also of O-horizons in moist tundra soils and cryoturbated soil horizons. A general characterization of SOM in an area of discontinuous permafrost shows that >70% of the SOC in the landscape is stored in SOM with a low degree of decomposition. Projections of permafrost thaw predict that the amount of SOC stored in the active layer of permafrost soils in this area could double by the end of this century. A lateral expansion of current thermokarst lakes by 30 m would expose comparable amounts of SOC to degradation. The results from this thesis have demonstrated the value of high-resolution studies of SOC storage. It is found that peat plateaus, common in the sporadic and discontinuous permafrost zones, store large quantities of labile SOM and may be highly susceptible to permafrost degradation, especially thermokarst, under future climate warming. Large quantities of labile SOM is also stored in cryoturbated soil horizons which may be affected by active layer warming and deepening. The current upscaling methodology is statistically evaluated and recommendations are given for the design of future studies. To accurately predict responses of periglacial C pools to a warming climate detailed studies of SOC storage and partitioning in different periglacial landscapes are needed.

  • 16.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Soil organic carbon in permafrost terrain: Total storage, landscape distribution and environmental controls2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    High latitude terrestrial ecosystems are considered key components in the global carbon (C) cycle and hold large reservoirs of soil organic carbon (SOC). To a large degree, this SOC is stored in permafrost soils and peatlands and is vulnerable to remobilization under future global warming and permafrost thawing. Recent studies estimate that soils in permafrost regions store SOC equivalent to ~ 1.5 times the global atmospheric C pool. Ecosystems and soils interact with the atmospheric C pool; photosynthesis sequesters CO2 into SOC whereas microbial decomposition releases C based trace gases (mainly CO2 and CH4). Because of the radiative greenhouse properties of these gases, soil processes also feedback on the global climate system. Recent studies report increases in permafrost temperatures and under future climate change scenarios permafrost environments stand to undergo further changes. As permafrost thaws and surface hydrology changes, there is concern that periglacial tundra and peatland ecosystems will switch from being sinks for atmospheric C into sources, creating a potential for positive feedbacks on global warming. The magnitude of change in C fluxes resulting from climate warming and permafrost thawing depends on the remobilization processes affecting SOC stores, the size of SOC stores that become available for remobilization and the lability of the SOM compounds in these stores. While the large size and potential vulnerability of arctic SOC reservoirs is recognized, detailed knowledge on the landscape partitioning and quality of this SOC is poor.

    Paper I of this thesis assesses landscape allocation and environmental gradients in SOC storage in the Usa River Basin lowlands of northeastern European Russia. The Russian study area ranges from taiga region with isolated permafrost patches to tundra region with nearly continuous permafrost. Paper II of this thesis investigates total storage, landscape partitioning and quality of soil organic carbon (SOC) in the tundra and continuous permafrost terrain of the Tulemalu Lake area in the Central Canadian Arctic. Databases on soil properties, permafrost, vegetation and modeled climate are compiled and analyzed. Mean SOC storage in the two study regions is 38.3 kg C m-2 for the Usa River Basin and 33.8 kg C m-2 for Tulemalu Lake (for 1m depth in mineral soils and total depth of peat deposits). Both estimates are higher than previous estimates for the same study areas. Multivariate gradient analyses from the Usa Basin show that local vegetation and permafrost are strong predictors of soil chemical properties, overshadowing the effect of climate variables. The results highlight the importance of peatlands, particularly bogs, in bulk SOC storage in all types of permafrost terrain. In the Tulemalu Lake area significant amounts of SOC is stored in cryoturbated soil horizons with C/N ratios indicating a relatively low degree of decomposition. As this pool of cryoturbated SOC is mainly stored in the active layer, no dramatic increases in remobilization are expected following a deepening of the active layer. However, recent studies have demonstrated the importance of SOC storage in deep (>1m) cryoturbated horizons. Perennially frozen peat deposits in permafrost bogs constitute the main vulnerable SOC pool in the investigated regions. Remobilization of this frozen C can occur through gradual but widespread deepening of the active layer with subsequent talik formation, or through more rapid but localized thermokarst erosion.

  • 17.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Spatial upscaling using thematic maps: an analysis of uncertainties in permafrost soil carbon estimates2012In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 26, p. GB2026-Article in journal (Refereed)
    Abstract [en]

    Studies of periglacial regions confirm their importance in the global carbon (C) cycle, but estimates of ecosystem C storage or green-house gas fluxes from these remote areas are generally poorly constrained and quantitative estimates of upscaling uncertainties are lacking. In this study, a regional database describing soil organic carbon (SOC) storage in periglacial terrain (European Russian Arctic) was used to evaluate spatial upscaling from point measurements using thematic maps. The selection of classes for upscaling and the need for replication in soil sampling were statistically evaluated. Upscaling using a land cover classification and a soil map estimated SOC storage to 48.5 and 47.0 kg C m(-2), respectively with 95% confidence intervals (CI) within +/- 8%. When corrected for spatial errors in the LCC upscaling proxy, SOC was estimated to 46.5 kg C m(-2) with a 95% CI reflecting propagated variance from both natural variability and spatial errors of +/- 11%. Artificially decreasing the size of the database used for upscaling showed that relatively stable results could be achieved with lower replication in some upscaling classes. Decreased spatial resolution for upscaling from 30 m to 1 km had little impact on SOC estimates in this region, but classification accuracy was dramatically reduced and land cover classes show different, sometimes nonlinear, responses to scale. The methods and recommendations presented here can provide guidelines for any future study where point observations of a variable are upscaled using remotely sensed thematic maps or classifications and potential applications for circum-arctic studies are discussed. For future upscaling studies at large geographic scales, a priori determination of sample sizes and tests to insure unimodal and statistically independent samples are recommended. If these prerequisites are not fulfilled, classes may be merged or subdivided prior to upscaling.

  • 18.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Uncertainty analysis for estimates of soil organic carbon storage in permafrost terrain, a regionalstudy from the western Russian Arctic2011Conference paper (Other academic)
    Abstract [en]

    Studies of periglacial regions confirm their importance in the global carbon (C) cycle,but estimates of e.g. soil organic carbon (SOC) storage are poorly constrained and lack quantitativeestimates of errors following upscaling. In this study, a comprehensive regional SOC database from thenorthern Usa River Basin (European Russian Arctic, 55 000 km2) is used to evaluate the currentmethodology of SOC upscaling in periglacial terrain. The selection of classes for upscaling and the need forreplication in soil sampling are statistically evaluated. Upscaling using a land cover classification and a soilmap estimates SOC storage at 48.5 and 47.0 kg C m-2, respectively with 95% confidence intervals (CI)within ±8%. When corrected for spatial errors in the upscaling proxy, SOC is estimated to 46.5 kg C m-2with a 95% CI reflecting propagated variance from both natural variability and spatial errors of ±11%.Artificially decreasing the size of the database used for upscaling shows that relatively stable results can beachieved with lower replication in some upscaling classes. For future upscaling studies at large geographicscales, a priori determination of sample sizes and tests to insure unimodal and statistically independentsamples are recommended. If these prerequisites are not fulfilled, classes may be merged or subdividedprior to upscaling. Decreased spatial resolution for upscaling from 30 m to 1 km has little impact on SOCestimates in this region, but classification accuracy is dramatically reduced and land cover classes show different, sometimes non-linear, responses to scale.

  • 19.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Landscape partitioning and environmental gradient analyses of soil organic carbon in a permafrost environment2009In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 23, no GB3006Article in journal (Refereed)
    Abstract [en]

    This study investigates landscape allocation and environmental gradients in soil organic carbon (C) storage in northeastern European Russia. The lowlands of the investigated Usa River Basin range from taiga with isolated permafrost to tundra vegetation on continuous permafrost. We compile and analyze databases on soil properties, permafrost, vegetation, and modeled climate. Mean soil C storage is estimated at 38.3 kg C m−2, with similar amounts in taiga and tundra regions. Permafrost soils hold 42% of the total soil C in the area. Peatlands dominate soil C storage with 72% of the total pool and 98% of permafrost C. Multivariate gradient analyses show that local vegetation and permafrost are strong predictors of soil chemical properties, overshadowing the effect of climate variables. This study highlights the importance of peatlands, particularly bogs, in bulk soil C storage. Soil organic matter stored in permafrost has higher C:N ratios than unfrozen material. Permafrost bogs constitute the main vulnerable C pool in the region. Remobilization of this frozen C can occur through gradual but widespread deepening of the active layer with subsequent talik formation or through more rapid but localized thermokarst erosion.

  • 20.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Patterns in Soil C Distribution in the Usa Basin (Russia): Linking Soil Properties to Environmental Variables in Constrained Gradient Analysis2008In: Ninth International Conference on Permafrost: Extended Abstracts, 2008, p. 105-106Conference paper (Other academic)
  • 21.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Kaverin, Dmitry
    Virtanen, Tarmo
    Estimating soil organic carbon storage in periglacial terrain at very high resolution; a case study from the European Russian Arctic2010Conference paper (Other academic)
    Abstract [en]

     

    1    Introduction

     

    While recent research advances have significantly increased our understanding of SOC storage in the periglacial landscape, there are still many uncertainties. Local scale studies have shown that the landscape distribution of SOC is highly heterogeneous (e.g. Hugelius and Kuhry, 2009). Some landscape components, such as peat deposits or cryoturbated soil horizons, can dominate local SOC storage.  However, there are no clear trends in landscape distribution and regional differences emerge (Kuhry et al., in prep.).

    We have conducted a very high resolution study of SOC storage in four study sites (Seida and Rogovaya 1-3) in discontinuous permafrost terrain, European Russian Arctic. Point pedon data is upscaled to areal coverage using two different upscaling tools, land cover classifications and soil maps.

    2      Methods

    2.1     Soil sampling and upscaling

    Soil sampling was performed (i) along landscape transects and (ii) according to a weighted, stratified random sampling program. Sampling was done in 10 cm increments to 1 m depth or to full depth of peat deposits in a total of 94 sites.

    Point pedon data is upscaled to areal coverage using two different upscaling tools:

    1. Thematic land cover classifications based on multiresolution segmentation of high-resolution Quickbird imagery (2.44 m raster resolution, 17 separate land cover classes, software Definiens Professional 5.0) and:

    2. High resolution thematic soil maps following World Reference Base for Soil Resources terminology (20 distinct soil types, median polygon size 1960 m2).

    Mean SOC storage for each land cover or soil type is multiplied by the areal coverage within the study areas to calculate total storage and landscape partitioning of SOC.

    Figure 1 illustrates the spatial resolution of the two upscaling tools. It also shows 4 pixels of Landsat TM resolution, representing the highest resolution of previous land cover based SOC storage studies in permafrost terrain.

    3      results

     

    Preliminary calculations show that the estimates in the four different areas are between 38-58 kg C m-2 for land cover upscaling and between 37-49 kg C m-2 for soil map upscaling. Both upscaling methods yield higher estimates than what has previously been reported for this area (Hugelius and Kuhry, 2009). A majority of SOC is stored in Cryic Histosols or Folic/Histic Cryosols. Contiguous permafrost peat plateaus are present in all study areas, covering ~20-30 % of the landscape. The mean depth of peat deposits in the four plateaus is between 150-250 cm, but it is highly variable (recorded range 30-420 cm).

    There is no evidence of any significant deep burial of SOC through cryoturbation processes.

    References

    Hugelius G. and Kuhry P. 2009, Landscape partitioning and environmental gradient analyses of soil organic carbon in a permafrost environment. Global Biogeochemical Cycles, 23, GB3006, doi:10.1029/2008GB003419.

    Kuhry, P., Dorrepaal, E., Hugelius G., Schuur, E.A.G. and Tarnocai C., Potential remobilization of permafrost carbon under future global warming. Permafrost and Periglacial Processes, Submitted.

  • 22.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Tarnocai, Charles
    Ideas and perspectives: Holocene thermokarst sediments of the Yedoma permafrost region do not increase the northern peatland carbon pool2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 7, p. 2003-2010Article in journal (Refereed)
    Abstract [en]

    Permafrost deposits in the Beringian Yedoma region store large amounts of organic carbon (OC). Walter Anthony et al. (2014) describe a previously unrecognized pool of 159 Pg OC accumulated in Holocene thermokarst sediments deposited in Yedoma region alases (thermokarst depressions). They claim that these alas sediments increase the previously recognized circumpolar permafrost peat OC pool by 50 %. It is stated that previous integrated studies of the permafrost OC pool have failed to account for these deposits because the Northern Circumpolar Soil Carbon Database (NCSCD) is biased towards non-alas field sites and that the soil maps used in the NCSCD underestimate coverage of organic permafrost soils. Here we evaluate these statements against a brief literature review, existing data sets on Yedoma region soil OC storage and independent field-based and geospatial data sets of peat soil distribution in the Siberian Yedoma region. Our findings are summarized in three main points. Firstly, the sediments described by Walter Anthony et al. (2014) are primarily mineral lake sediments and do not match widely used international scientific definitions of peat or organic soils. They can therefore not be considered an addition to the circumpolar peat carbon pool. We also emphasize that a clear distinction between mineral and organic soil types is important since they show very different vulnerability trajectories under climate change. Secondly, independent field data and geospatial analyses show that the Siberian Yedoma region is dominated by mineral soils, not peatlands. Thus, there is no evidence to suggest any systematic bias in the NCSCD field data or maps. Thirdly, there is spatial overlap between these Holocene thermokarst sediments and previous estimates of permafrost soil and sediment OC stocks. These carbon stocks were already accounted for by previous studies and they do not significantly increase the known circumpolar OC pool. We suggest that these inaccurate statements made in Walter Anthony et al. (2014) mainly resulted from misunderstandings caused by conflicting definitions and terminologies across different geoscientific disciplines. A careful cross-disciplinary review of terminologies would help future studies to appropriately harmonize definitions between different fields.

  • 23.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Tarnocai, Charles
    Virtanen, Tarmo
    Soil Organic Carbon Pools in a Periglacial Landscape; a Case Study from the Central Canadian Arctic2010In: Permafrost and Periglacial Processes, ISSN 1045-6740, E-ISSN 1099-1530, Vol. 21, no 1, p. 16-29Article in journal (Refereed)
    Abstract [en]

    We investigated total storage and landscape partitioning of soil organic carbon (SOC) in continuous permafrost terrain, central Canadian Arctic. The study is based on soil chemical analyses of pedons sampled to 1-m depth at 35 individual sites along three transects. Radiocarbon dating of cryoturbated soil pockets, basal peat and fossil wood shows that cryoturbation processes have been occurring since the Middle Holocene and that peat deposits started to accumulate in a forest-tundra environment where spruce was present (∼6000 cal yrs BP). Detailed partitioning of SOC into surface organic horizons, cryoturbated soil pockets and non-cryoturbated mineral soil horizons is calculated (with storage in active layer and permafrost calculated separately) and explored using principal component analysis. The detailed partitioning and mean storage of SOC in the landscape are estimated from transect vegetation inventories and a land cover classification based on a Landsat satellite image. Mean SOC storage in the 0–100-cm depth interval is 33.8 kg C m−2, of which 11.8 kg C m−2 is in permafrost. Fifty-six per cent of the total SOC mass is stored in peatlands (mainly bogs), but cryoturbated soil pockets in Turbic Cryosols also contribute significantly (17%). Elemental C/N ratios indicate that this cryoturbated soil organic matter (SOM) decomposes more slowly than SOM in surface O-horizons.

  • 24.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Tarnocai, Charles
    Virtanen, Tarmo
    Total Storage and Landscape Distribution of Soil Carbon in the Central Canadian Arctic Using Different Upscaling Tools2008Conference paper (Other academic)
  • 25.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Tarnocai, Charles
    Virtanen, Tarmo
    Total Storage and Landscape Distribution of Soil Carbon in the Central Canadian Arctic Using Different Upscaling Tools2009In: Geophysical Research Abstracts vol. 11, 2009, p. EGU2009-9573Conference paper (Other academic)
  • 26.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Virtanen, Tarmo
    University of Helsinki.
    Kaverin, Dmitry
    Komi Science Centre.
    Pastukhov, Alexander
    Komi Science Centre.
    Rivkin, Felix
    Institute FSUE Fundamentprojekt.
    Marchenko, Sergey
    University of Alaska Fairbanks.
    Romanovsky, Vladimir
    University of Alaska Fairbanks.
    High‐resolution mapping of ecosystem carbon storageand potential effects of permafrost thaw in periglacialterrain, European Russian Arctic2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116Article in journal (Refereed)
    Abstract [en]

    This study describes detailed partitioning of phytomass carbon (C) and soil organiccarbon (SOC) for four study areas in discontinuous permafrost terrain, Northeast EuropeanRussia. The mean aboveground phytomass C storage is 0.7 kg C m−2. Estimated landscapeSOC storage in the four areas varies between 34.5 and 47.0 kg C m−2 with LCC (landcover classification) upscaling and 32.5–49.0 kg C m−2 with soil map upscaling. A nestedupscaling approach using a Landsat thematic mapper land cover classification for thesurrounding region provides estimates within 5 ± 5% of the local high‐resolutionestimates. Permafrost peat plateaus hold the majority of total and frozen SOC, especially inthe more southern study areas. Burying of SOC through cryoturbation of O‐ or A‐horizonscontributes between 1% and 16% (mean 5%) of total landscape SOC. The effect ofactive layer deepening and thermokarst expansion on SOC remobilization is modeled forone of the four areas. The active layer thickness dynamics from 1980 to 2099 is modeledusing a transient spatially distributed permafrost model and lateral expansion of peatplateau thermokarst lakes is simulated using geographic information system analyses.Active layer deepening is expected to increase the proportion of SOC affected by seasonalthawing from 29% to 58%. A lateral expansion of 30 m would increase the amount ofSOC stored in thermokarst lakes/fens from 2% to 22% of all SOC. By the end of thiscentury, active layer deepening will likely affect more SOC than thermokarst expansion,but the SOC stores vulnerable to thermokarst are less decomposed.

  • 27.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Routh, Joyanto
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Characterization of Soil Organic Matter in Permafrost Terrain – landscape scale analyses from the European Russian Arctic2010Conference paper (Other academic)
    Abstract [en]

     

    1      Introduction

     

    Soils of high latitude terrestrial ecosystems are considered key components in the global carbon cycle and hold large stores of Soil Organic Carbon (SOC). The absolute and relative sizes of labile and recalcitrant SOC pools in periglacial terrain are mostly unknown (Kuhry et al. in prep.). Such data has important policy relevance because of its impact on climate change.

    We sampled soils representative of all major land cover and soil types in discontinuous permafrost terrain, European Russian Arctic. We analyzed the bulk soil characteristics including the soil humic fraction to assess the recalcitrance in organic matter quality in down-depth soil profiles.

    2      METHODS

     

    A comprehensive stratified random soil sampling program was carried out in the Seida area during late summer 2008. From these, we selected nine sites considered representative for the landscape. Active layer and permafrost free upland soils were sampled from dug soil pits with fixed volume corers. Peat plateaus were sampled near thermally eroding edges. Permafrost soils were cored using steel pipes hammered into the frozen peat. Permafrost free fens were sampled using fixed volume Russian corers.

    Radiocarbon dating was used to determine the SOC ages. The soils were analyzed for dry bulk density, elemental content, and stable isotope composition of organic C and N (δ13C, and δ15N). Further, humic acids were extracted, and the degree of humification of SOM assessed based on A600/C and ∆ log K (Ikeya and Watanabe, 2003).

    3      results

     

    Figure 1 shows soil organic matter (SOM) characteristics in a peat sequence from one of the nine described sites, a raised bog peat plateau.

    The peatland first developed as a permafrost-free fen during the Holocene Hypsithermal. Permafrost only aggraded in the late Holocene. Anoxic conditions in the fen and permafrost in peat plateau stages reduced decomposition rates and the degree of humification (A600/C) is relatively constant throughout the peat deposit.

    Botanical origin is a key factor in determining SOM quality, which is clearly reflected in the elemental ratio (C/N) and isotopic composition of C and N. There are sharp shifts in humification, C/N and isotopic composition at the peat/clay interface.

    References

    Ikeya, K. and Watanabe, A., 2003, Direct expression of an index for the degree of humification of humic acids using organic carbon concentration. Soil Science and Plant Nutrition, 49: 47-53.

    Kuhry, P., Dorrepaal, E., Hugelius G., Schuur, E.A.G. and Tarnocai C., Potential remobilization of permafrost carbon under future global warming. Permafrost and Periglacial Processes, Submitted.

  • 28.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Routh, Joyanto
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mapping the degree of decomposition and thaw remobilization potential of soil organic matter in discontinuous permafrost terrain2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. G02030-Article in journal (Refereed)
    Abstract [en]

    Soil organic matter (SOM) stored in permafrost terrain is a key component in the global carbon cycle, but its composition and lability are largely unknown. We characterize and assess the degree of decomposition of SOM at nine sites representing major land-cover and soil types (including peat deposits) in an area of discontinuous permafrost in the European Russian Arctic. We analyze the elemental and stable isotopic composition of bulk SOM, and the degree of humification and elemental composition of humic acids (HA). The degree of decomposition is low in the O-horizons of mineral soils and peat deposits. In the permafrost free non-peatland soils there is enrichment of C-13 and N-15, and decrease in bulk C/N ratios indicating more decomposed material with depth. Spectral characterization of HA indicates low humification in O-horizons and peat deposits, but increase in humification in the deeper soil horizons of non-peatland soils, and in mineral horizons underlying peat deposits. GIS based maps indicate that less decomposed OM characteristic of the O-horizon and permafrost peat deposits constitute the bulk of landscape SOM (>70% of landscape soil C). We conclude, however, that permafrost has not been the key environmental factor controlling the current degree of decomposition of SOM in this landscape due to relatively recent permafrost aggradation. In this century, active layer deepening will mainly affect SOM with a relatively high degree of decomposition in deeper mineral soil horizons. Additionally, thawing permafrost in peat plateaus may cause rapid remobilization of less decomposed SOM through thermokarst expansion.

  • 29.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Routh, Joyanto
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Patrick, Crill
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chemical characteristics and lability of soil organic matter in permafrost terrain, European Russian ArcticManuscript (preprint) (Other academic)
  • 30.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Strauss, J.
    Zubrzycki, S.
    Harden, J. W.
    Schuur, E. A. G.
    Ping, C. -L
    Schirrmeister, L.
    Grosse, G.
    Michaelson, G. J.
    Koven, C. D.
    O'Donnell, J. A.
    Elberling, B.
    Mishra, U.
    Camill, P.
    Yu, Z.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 23, p. 6573-6593Article in journal (Refereed)
    Abstract [en]

    Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but SOC stock estimates were poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of permafrost SOC stocks, including quantitative uncertainty estimates, in the 0-3m depth range in soils as well as for sediments deeper than 3m in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. Revised estimates are based on significantly larger databases compared to previous studies. Despite this there is evidence of significant remaining regional data gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for deposits below 3mdepth in deltas and the Yedoma region. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are substantial differences in other components, including the fraction of perennially frozen SOC. Upscaled based on regional soil maps, estimated permafrost region SOC stocks are 217 +/- 12 and 472 +/- 27 Pg for the 0-0.3 and 0-1 m soil depths, respectively (+/- 95% confidence intervals). Storage of SOC in 0-3m of soils is estimated to 1035 +/- 150 Pg. Of this, 34 +/- 16 PgC is stored in poorly developed soils of the High Arctic. Based on generalized calculations, storage of SOC below 3m of surface soils in deltaic alluvium of major Arctic rivers is estimated as 91 +/- 52 Pg. In the Yedoma region, estimated SOC stocks below 3mdepth are 181 +/- 54 Pg, of which 74 +/- 20 Pg is stored in intact Yedoma (late Pleistocene ice-and organic-rich silty sediments) with the remainder in refrozen thermokarst deposits. Total estimated SOC storage for the permafrost region is similar to 1300 Pg with an uncertainty range of similar to 1100 to 1500 Pg. Of this, similar to 500 Pg is in non-permafrost soils, seasonally thawed in the active layer or in deeper taliks, while similar to 800 Pg is perennially frozen. This represents a substantial similar to 300 Pg lowering of the estimated perennially frozen SOC stock compared to previous estimates.

  • 31.
    Hugelius, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Virtanen, Tarmo
    Kaverin, Dmitry
    Pastukhov, Alexander
    Rivkin, Felix
    Marchenko, Sergey
    Romanovsky, Vladimir
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    High-resolution mapping of ecosystem carbon storage and potential effects of permafrost thaw in periglacial terrain, European Russian Arctic2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. G03024-Article in journal (Refereed)
    Abstract [en]

    This study describes detailed partitioning of phytomass carbon (C) and soil organic carbon (SOC) for four study areas in discontinuous permafrost terrain, Northeast European Russia. The mean aboveground phytomass C storage is 0.7 kg C m(-2). Estimated landscape SOC storage in the four areas varies between 34.5 and 47.0 kg C m(-2) with LCC (land cover classification) upscaling and 32.5-49.0 kg C m(-2) with soil map upscaling. A nested upscaling approach using a Landsat thematic mapper land cover classification for the surrounding region provides estimates within 5 +/- 5% of the local high-resolution estimates. Permafrost peat plateaus hold the majority of total and frozen SOC, especially in the more southern study areas. Burying of SOC through cryoturbation of O- or A-horizons contributes between 1% and 16% (mean 5%) of total landscape SOC. The effect of active layer deepening and thermokarst expansion on SOC remobilization is modeled for one of the four areas. The active layer thickness dynamics from 1980 to 2099 is modeled using a transient spatially distributed permafrost model and lateral expansion of peat plateau thermokarst lakes is simulated using geographic information system analyses. Active layer deepening is expected to increase the proportion of SOC affected by seasonal thawing from 29% to 58%. A lateral expansion of 30 m would increase the amount of SOC stored in thermokarst lakes/fens from 2% to 22% of all SOC. By the end of this century, active layer deepening will likely affect more SOC than thermokarst expansion, but the SOC stores vulnerable to thermokarst are less decomposed.

  • 32.
    Humborg, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Estrup Andersen, Hans
    Blenckner, Thorsten
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Gadegast, Mathias
    Giesler, Reiner
    Hartmann, Jens
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Huerdler, Jens
    Kortelainen, Pirkko
    Blicher-Mathiesen, Gitte
    Venohr, Markus
    Weyhenmeyer, Gesa
    Environmental Impacts - Freshwater Biogeochemistry2015In: Second Assessment of Climate Change for the Baltic Sea Basin / [ed] The BACC II Author Team, Springer, 2015, p. 307-336Chapter in book (Refereed)
    Abstract [en]

    Climate change effects on freshwater biogeochemistry and riverine loads of biogenic elements to the Baltic Sea are not straight forward and are difficult to distinguish from other human drivers such as atmospheric deposition, forest and wetland management, eutrophication and hydrological alterations. Eutrophication is by far the most well-known factor affecting the biogeochemistry of the receiving waters in the various sub-basins of the Baltic Sea. However, the present literature review reveals that climate change is a compounding factor for all major drivers of freshwater biogeochemistry discussed here, although evidence is still often based on short-term and/or small-scale studies.

  • 33. Jackson, Robert B.
    et al.
    Lajtha, Kate
    Crow, Susan E.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Kramer, Marc G.
    Piñeiro, Gervasio
    The Ecology of Soil Carbon: Pools, Vulnerabilities, and Biotic and Abiotic Controls2017In: Annual Review of Ecology, Evolution and Systematics, ISSN 1543-592X, E-ISSN 1545-2069, Vol. 48, p. 419-445Article, book review (Refereed)
    Abstract [en]

    Soil organic matter (SOM) anchors global terrestrial productivity and food and fiber supply. SOM retains water and soil nutrients and stores more global carbon than do plants and the atmosphere combined. SOM is also decomposed by microbes, returning CO2, a greenhouse gas, to the atmosphere. Unfortunately, soil carbon stocks have been widely lost or degraded through land use changes and unsustainable forest and agricultural practices. To understand its structure and function and to maintain and restore SOM, we need a better appreciation of soil organic carbon (SOC) saturation capacity and the retention of above-and belowground inputs in SOM. Our analysis suggests root inputs are approximately five times more likely than an equivalent mass of aboveground litter to be stabilized as SOM. Microbes, particularly fungi and bacteria, and soil faunal food webs strongly influence SOM decomposition at shallower depths, whereas mineral associations drive stabilization at depths greater than similar to 30 cm. Global uncertainties in the amounts and locations of SOM include the extent of wetland, peatland, and permafrost systems and factors that constrain soil depths, such as shallow bedrock. In consideration of these uncertainties, we estimate global SOC stocks at depths of 2 and 3 m to be between 2,270 and 2,770 Pg, respectively, but could be as much as 700 Pg smaller. Sedimentary deposits deeper than 3 m likely contain >500 Pg of additional SOC. Soils hold the largest biogeochemically active terrestrial carbon pool on Earth and are critical for stabilizing atmospheric CO2 concentrations. Nonetheless, global pressures on soils continue from changes in land management, including the need for increasing bioenergy and food production.

  • 34.
    Kaislahti Tillman, Päivi
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holzkämper, Steffen
    Andersen, Thorbjoern Joest
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Oksanen, Pirita
    Stable isotope records of Sphagnum fuscum peat as late Holocene climate proxies in north-eastern European RussiaManuscript (preprint) (Other academic)
  • 35.
    Kaislahti Tillman, Päivi
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Joest Andersen, Thorbjörn
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Oksanen, Pirita
    Stable isotopes in Sphagnum fuscum peat as late-Holocene climate proxies in northeastern European Russia2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 10, p. 1381-1390Article in journal (Refereed)
    Abstract [en]

    The environment of the northern taiga to tundra transition is highly sensitive to climate fluctuations. In this study from northeastern European Russia, stable carbon and oxygen isotope ratios (δ13C, δ18O) in α-cellulose of Sphagnum fuscum stems subsampled from hummocks and peat plateau profiles have been used as climate proxies. The entire isotope time series, dated by lead (210Pb), caesium (137Cs) and AMS-radiocarbon (14C) dating, spans the past 2500 years. Plant macrofossil analyses were used as an aid in single species selection, but are also helpful in identifying past surface moisture conditions. The most significant relationships were found between the recent δ13C record and summer (July–August) temperatures (R 2 = 0.58, p < 0.01), and the recent δ18O record and winter (October–May) precipitation anomalies in the tundra region (R 2 = 0.36, p < 0.01). The study demonstrates that stable isotopes preserved in northern peat deposits are useful indicators for summer temperature and winter precipitation at decadal to millennial timescales.

  • 36. Koven, C. D.
    et al.
    Schuur, E. A. G.
    Schaedel, C.
    Bohn, T. J.
    Burke, E. J.
    Chen, G.
    Chen, X.
    Ciais, P.
    Grosse, G.
    Harden, J. W.
    Hayes, D. J.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jafarov, E. E.
    Krinner, G.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lawrence, D. M.
    MacDougall, A. H.
    Marchenko, S. S.
    McGuire, A. D.
    Natali, S. M.
    Nicolsky, D. J.
    Olefeldt, D.
    Peng, S.
    Romanovsky, V. E.
    Schaefer, K. M.
    Strauss, J.
    Treat, C. C.
    Turetsky, M.
    A simplified, data-constrained approach to estimate the permafrost carbon-climate feedback2015In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 373, no 2054, article id 20140423Article in journal (Refereed)
    Abstract [en]

    We present an approach to estimate the feedback from large-scale thawing of permafrost soils using a simplified, data-constrained model that combines three elements: soil carbon (C) maps and profiles to identify the distribution and type of C in permafrost soils; incubation experiments to quantify the rates of C lost after thaw; and models of soil thermal dynamics in response to climate warming. We call the approach the Permafrost Carbon Network Incubation-Panarctic Thermal scaling approach (PInc-PanTher). The approach assumes that C stocks do not decompose at all when frozen, but once thawed follow set decomposition trajectories as a function of soil temperature. The trajectories are determined according to a three-pool decomposition model fitted to incubation data using parameters specific to soil horizon types. We calculate litterfall C inputs required to maintain steady-state C balance for the current climate, and hold those inputs constant. Soil temperatures are taken from the soil thermal modules of ecosystem model simulations forced by a common set of future climate change anomalies under two warming scenarios over the period 2010 to 2100. Under a medium warming scenario (RCP4.5), the approach projects permafrost soil C losses of 12.2-33.4 Pg C; under a high warming scenario (RCP8.5), the approach projects C losses of 27.9-112.6 Pg C. Projected C losses are roughly linearly proportional to global temperature changes across the two scenarios. These results indicate a global sensitivity of frozen soil C to climate change (gamma sensitivity) of -14 to -19 PgC degrees C-1 on a 100 year time scale. For CH4 emissions, our approach assumes a fixed saturated area and that increases in CH4 emissions are related to increased heterotrophic respiration in anoxic soil, yielding CH4 emission increases of 7% and 35% for the RCP4.5 and RCP8.5 scenarios, respectively, which add an additional greenhouse gas forcing of approximately 10-18%. The simplified approach presented here neglects many important processes that may amplify or mitigate C release from permafrost soils, but serves as a data-constrained estimate on the forced, large-scale permafrost C response to warming.

  • 37. Koven, Charles D.
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Lawrence, David M.
    Wieder, William R.
    Higher climatological temperature sensitivity of soil carbon in cold than warm climates2017In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 7, no 11, p. 817-822Article in journal (Refereed)
    Abstract [en]

    The projected loss of soil carbon to the atmosphere resulting from climate change is a potentially large but highly uncertain feedback to warming. The magnitude of this feedback is poorly constrained by observations and theory, and is disparately represented in Earth system models (ESMs)(1-3). To assess the climatological temperature sensitivity of soil carbon, we calculate apparent soil carbon turnover times(4) that reflect long-term and broad-scale rates of decomposition. Here, we show that the climatological temperature control on carbon turnover in the top metre of global soils is more sensitive in cold climates than in warm climates and argue that it is critical to capture this emergent ecosystem property in global-scale models. We present a simplified model that explains the observed high cold-climate sensitivity using only the physical scaling of soil freeze-thaw state across climate gradients. Current ESMs fail to capture this pattern, except in anESMthat explicitly resolves vertical gradients in soil climate and carbon turnover. An observed weak tropical temperature sensitivity emerges in a different model that explicitly resolves mineralogical control on decomposition. These results support projections of strong carbon- climate feedbacks from northern soils(5,6) and demonstrate a method for ESMs to capture this emergent behaviour.

  • 38.
    Kuhry, P.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Dorrepaal, E.
    Hugelius, G.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Schuur, E. A. G.
    Tarnocai, C.
    Potential Remobilization of Belowground Permafrost Carbon under Future Global Warming2010In: Permafrost and Periglacial Processes, ISSN 1045-6740, E-ISSN 1099-1530, Vol. 21, no 2, p. 208-214Article in journal (Refereed)
    Abstract [en]

    Research on permafrost carbon has dramatically increased in the past few years. A new estimate of 1672 Pg C of belowground organic carbon in the northern circumpolar permafrost region more than doubles the previous value and highlights the potential role of permafrost carbon in the Earth System. Uncertainties in this new estimate remain due to relatively few available pedon data for certain geographic sectors and the deeper cryoturbated soil horizons, and the large polygon size in the soil maps used for upscaling. The large permafrost carbon pool is not equally distributed across the landscape: peat deposits, cryoturbated soils and the loess-like deposits of the yedoma complex contain disproportionately large amounts of soil organic matter, often exhibiting a low degree of decomposition. Recent findings in Alaska and northern Sweden provide strong evidence that the deeper soil carbon in permafrost terrain is starting to be released, supporting previous reports from Siberia. The permafrost carbon pool is not yet fully integrated in climate and ecosystem models and an important objective should be to define typical pedons appropriate for model setups. The thawing permafrost carbon feedback needs to be included in model projections of future climate change.

  • 39.
    Kuhry, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Grosse, G.
    Harden, J. W.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Koven, C. D.
    Ping, C-L
    Schirrmeister, L.
    Tarnocai, C.
    Characterisation of the Permafrost Carbon Pool2013In: Permafrost and Periglacial Processes, ISSN 1045-6740, E-ISSN 1099-1530, Vol. 24, no 2, p. 146-155Article in journal (Refereed)
    Abstract [en]

    The current estimate of the soil organic carbon (SOC) pool in the northern permafrost region of 1672 Petagrams (Pg) C is much larger than previously reported and needs to be incorporated in global soil carbon (C) inventories. The Northern Circumpolar Soil Carbon Database (NCSCD), extended to include the range 0-300cm, is now available online for wider use by the scientific community. An important future aim is to provide quantitative uncertainty ranges for C pool estimates. Recent studies have greatly improved understanding of the regional patterns, landscape distribution and vertical (soil horizon) partitioning of the permafrost C pool in the upper 3m of soils. However, the deeper C pools in unconsolidated Quaternary deposits need to be better constrained. A general lability classification of the permafrost C pool should be developed to address potential C release upon thaw. The permafrost C pool and its dynamics are beginning to be incorporated into Earth System models, although key periglacial processes such as thermokarst still need to be properly represented to obtain a better quantification of the full permafrost C feedback on global climate change.

  • 40.
    Lindgren, Amelie
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Lund University, Sweden.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Christensen, Torben R.
    Vandenberghe, Jef
    GIS-based Maps and Area Estimates of Northern Hemisphere Permafrost Extent during the Last Glacial Maximum2016In: Permafrost and Periglacial Processes, ISSN 1045-6740, E-ISSN 1099-1530, Vol. 27, no 1, p. 6-16Article in journal (Refereed)
    Abstract [en]

    This study presents GIS-based estimates of permafrost extent in the northern circumpolar region during the Last Glacial Maximum (LGM), based on a review of previously published maps and compilations of field evidence in the form of ice-wedge pseudomorphs and relict sand wedges. We focus on field evidence localities in areas thought to have been located along the past southern border of permafrost. We present different reconstructions of permafrost extent, with areal estimates of exposed sea shelf, ice sheets and glaciers, to assess areas of minimum, likely and maximum permafrost extents. The GIS-based mapping of these empirical reconstructions allows us to estimate the likely area of northern permafrost during the LGM as 34.5 million km(2) (which includes 4.7 million km(2) of permafrost on exposed coastal sea shelves). The minimum estimate is 32.7 million km(2) and the maximum estimate is 35.3 million km(2). The extent of LGM permafrost is estimated to have been between c. 9.1 to 11.7 million km(2) larger than its current extent on land (23.6 million km(2)). However, 2.4 million km(2) of the lost land area currently remains as subsea permafrost on the submerged coastal shelves. The LGM permafrost extent in the northern circumpolar region during the LGM was therefore about 33 percent larger than at present. The net loss of northern permafrost since the LGM is due to its disappearance in large parts of Eurasia, which is not compensated for by gains in North America in areas formerly covered by the Laurentide ice sheet.

  • 41. Loisel, Julie
    et al.
    van Bellen, Simon
    Pelletier, Luc
    Talbot, Julie
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm Univ, Dept Phys Geog, Stockholm, Sweden.
    Karran, Daniel
    Yu, Zicheng
    Nichols, Jonathan
    Holmquist, James
    Insights and issues with estimating northern peatland carbon stocks and fluxes since the Last Glacial Maximum2017In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 165, p. 59-80Article, review/survey (Refereed)
    Abstract [en]

    In this review paper, we identify and address key uncertainties related to four local and global controls of Holocene northern peatland carbon stocks and fluxes. First, we provide up-to-date estimates of the current northern peatland area (3.2 M km(2)) and propose a novel approach to reconstruct changes in the northern peatland area over time (Section 2). Second, we review the key methods and models that have been used to quantify total carbon stocks and methane emissions over time at the hemispheric scale, and offer new research directions to improve these calculations (Section 3). Our main proposed improvement relates to allocating different carbon stock and emission values for each of the two dominant vegetation assemblages (sedge and brown moss-dominated vs. Sphagnum-dominated peat). Third, we discuss and quantify the importance of basin heterogeneity in estimating peat volume at the local scale (Section 4.1). We also highlight the importance of age model selection when reconstructing carbon accumulation rates from a peat core (Section 4.2). Lastly, we introduce the role of biogeomorphological agents such as beaver activity in controlling carbon dynamics (Section 5.1) and review the newest research related to permafrost thaw (Section 5.2) and peat fire (Section 5.3) under climate change. Overall, this review summarizes new information from a broad range of peat-carbon studies, provides novel analysis of hemispheric-scale paleo datasets, and proposes new insights on how to translate peat-core data into carbon fluxes. It also identifies critical data gaps and research priorities, and many ways to consider and address them.

  • 42. Mishra, U.
    et al.
    Jastrow, J. D.
    Matamala, R.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Koven, C. D.
    Harden, J. W.
    Ping, C. L.
    Michaelson, G. J.
    Fan, Z.
    Miller, R. M.
    McGuire, A. D.
    Tarnocai, C.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Riley, W. J.
    Schaefer, K.
    Schuur, E. A. G.
    Jörgenson, M. T.
    Hinzman, L. D.
    Empirical estimates to reduce modeling uncertainties of soil organic carbon in permafrost regions: a review of recent progress and remaining challenges2013In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 8, no 3, p. 035020-Article in journal (Refereed)
    Abstract [en]

    The vast amount of organic carbon (OC) stored in soils of the northern circumpolar permafrost region is a potentially vulnerable component of the global carbon cycle. However, estimates of the quantity, decomposability, and combustibility of OC contained in permafrost-region soils remain highly uncertain, thereby limiting our ability to predict the release of greenhouse gases due to permafrost thawing. Substantial differences exist between empirical and modeling estimates of the quantity and distribution of permafrost-region soil OC, which contribute to large uncertainties in predictions of carbon-climate feedbacks under future warming. Here, we identify research challenges that constrain current assessments of the distribution and potential decomposability of soil OC stocks in the northern permafrost region and suggest priorities for future empirical and modeling studies to address these challenges.

  • 43. Muster, Sina
    et al.
    Roth, Kurt
    Langer, Moritz
    Lange, Stephan
    Aleina, Fabio Cresto
    Bartsch, Annett
    Morgenstern, Anne
    Grosse, Guido
    Jones, Benjamin
    Sannel, A. Britta K.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sjöberg, Ylva
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Günther, Frank
    Andresen, Christian
    Veremeeva, Alexandra
    Lindgren, Prajna R.
    Bouchard, Frédéric
    Lara, Mark J.
    Fortier, Daniel
    Charbonneau, Simon
    Virtanen, Tarmo A.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Siewert, Matthias B.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Riley, William J.
    Koven, Charles D.
    Boike, Julia
    PeRL: a circum-Arctic Permafrost Region Pond and Lake database2017In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 9, no 1, p. 317-348Article in journal (Refereed)
    Abstract [en]

    Ponds and lakes are abundant in Arctic permafrost lowlands. They play an important role in Arctic wetland ecosystems by regulating carbon, water, and energy fluxes and providing freshwater habitats. However, ponds, i. e., waterbodies with surface areas smaller than 1.0 x 10(4) m(2), have not been inventoried on global and regional scales. The Permafrost Region Pond and Lake (PeRL) database presents the results of a circum-Arctic effort to map ponds and lakes from modern (2002-2013) high-resolution aerial and satellite imagery with a resolution of 5m or better. The database also includes historical imagery from 1948 to 1965 with a resolution of 6m or better. PeRL includes 69 maps covering a wide range of environmental conditions from tundra to boreal regions and from continuous to discontinuous permafrost zones. Waterbody maps are linked to regional permafrost landscape maps which provide information on permafrost extent, ground ice volume, geology, and lithology. This paper describes waterbody classification and accuracy, and presents statistics of waterbody distribution for each site. Maps of permafrost landscapes in Alaska, Canada, and Russia are used to extrapolate waterbody statistics from the site level to regional landscape units. PeRL presents pond and lake estimates for a total area of 1.4 x 10(6) km(2) across the Arctic, about 17% of the Arctic lowland (<300ma. s.l.) land surface area. PeRL waterbodies with sizes of 1.0 x 10(6) m(2) down to 1.0 x 10(2) m(2) contributed up to 21% to the total water fraction. Waterbody density ranged from 1.0 x 10 to 9.4 x 10(1) km(-2). Ponds are the dominant waterbody type by number in all landscapes representing 45-99% of the total waterbody number. The implementation of PeRL size distributions in land surface models will greatly improve the investigation and projection of surface inundation and carbon fluxes in permafrost lowlands. Waterbody maps, study area boundaries, and maps of regional permafrost landscapes including detailed metadata are available at https://doi.pangaea.de/10.1594/PANGAEA.868349.

  • 44. Olefeldt, D.
    et al.
    Goswami, S.
    Grosse, G.
    Hayes, D.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    McGuire, A. D.
    Romanovsky, V. E.
    Sannel, A. Britta K.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Schuur, E. A. G.
    Turetsky, M. R.
    Circumpolar distribution and carbon storage of thermokarst landscapes2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 13043Article in journal (Refereed)
    Abstract [en]

    Thermokarst is the process whereby the thawing of ice- rich permafrost ground causes land subsidence, resulting in development of distinctive landforms. Accelerated thermokarst due to climate change will damage infrastructure, but also impact hydrology, ecology and biogeochemistry. Here, we present a circumpolar assessment of the distribution of thermokarst landscapes, defined as landscapes comprised of current thermokarst landforms and areas susceptible to future thermokarst development. At 3.6 x 10(6) km(2), thermokarst landscapes are estimated to cover similar to 20% of the northern permafrost region, with approximately equal contributions from three landscape types where characteristic wetland, lake and hillslope thermokarst landforms occur. We estimate that approximately half of the below-ground organic carbon within the study region is stored in thermokarst landscapes. Our results highlight the importance of explicitly considering thermokarst when assessing impacts of climate change, including future landscape greenhouse gas emissions, and provide a means for assessing such impacts at the circumpolar scale.

  • 45.
    Palmtag, Juri
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Cable, Stefanie
    Christiansen, Hanne H.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Landform partitioning and estimates of deep storage of soil organic matter in Zackenberg, Greenland2018In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 12, no 5, p. 1735-1744Article in journal (Refereed)
    Abstract [en]

    Soils in the northern high latitudes are a key component in the global carbon cycle, with potential feedback on climate. This study aims to improve the previous soil organic carbon (SOC) and total nitrogen (TN) storage estimates for the Zackenberg area (NE Greenland) that were based on a land cover classification (LCC) approach, by using geomorphological upscaling. In addition, novel organic carbon (OC) estimates for deeper alluvial and deltaic deposits (down to 300 cm depth) are presented. We hypothesise that land-forms will better represent the long-term slope and depositional processes that result in deep SOC burial in this type of mountain permafrost environments. The updated mean SOC storage for the 0-100 cm soil depth is 4.8 kg Cm-2, which is 42% lower than the previous estimate of 8.3 kg Cm-2 based on land cover upscaling. Similarly, the mean soil TN storage in the 0-100 cm depth decreased with 44% from 0.50 kg (+/- 0.1 CI) to 0.28 (+/- 0.1 CI) kg TN m(-2). We ascribe the differences to a previous areal overestimate of SOC- and TN-rich vegetated land cover classes. The landform-based approach more correctly constrains the depositional areas in alluvial fans and deltas with high SOC and TN storage. These are also areas of deep carbon storage with an additional 2.4 kg Cm-2 in the 100-300 cm depth interval. This research emphasises the need to consider geomorphology when assessing SOC pools in mountain permafrost landscapes.

  • 46.
    Palmtag, Juri
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Soil organic carbon storage in continuous permafrost terrain; two case studies from NE Greenlandand NE Siberia2011Conference paper (Other academic)
    Abstract [en]

    The northern circumpolar permafrost region occupies about 16% of the global soil areaand holds approximately 50% of the global belowground soil organic carbon (SOC). We describe thequantity and quality of soil organic matter (SOM) in two areas of continuous permafrost in NE Greenland andNE Siberia. The main emphasis lies on the role of cryoturbation and Pleistocene loess-like deposits(yedoma) for SOC storage. This study is based on field work in three different study sites: Zackenberg(Greenland) and Shalaurovo and Chersky (Siberia), as well as laboratory analysis and radiocarbon dating.The estimated mean SOC storage in the upper meter of soil for Zackenberg is 10.5 kg C m-2 with 16% incryoturbated soil pockets. In Shalaurovo, the mean SOC storage is 29.0 kg C m-2 and in Chersky 21.7 kg Cm-2 with more than 30% stored in cryoturbated soil pockets. The study also presents new analyses for deepyedoma deposits(down to 5 m depth). Data from these sites show that the dry bulk densities are muchlower (due to excess ground ice) than those previously reported in the literature, leading to lower estimatesof SOC storage in these deposits.

  • 47.
    Palmtag, Juri
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lashchinskiy, Nikolay
    Tamstorf, Mikkel P.
    Richter, Andreas
    Elberling, Bo
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Storage, Landscape Distribution, and Burial History of Soil Organic Matter in Contrasting Areas of Continuous Permafrost2015In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 47, no 1, p. 71-88Article in journal (Refereed)
    Abstract [en]

    This study describes and compares soil organic matter (SOM) quantity and characteristics in two areas of continuous permafrost, a mountainous region in NE Greenland (Zackenberg study site) and a lowland region in NE Siberia (Cherskiy and Shalaurovo study sites). Our assessments are based on stratified-random landscape-level inventories of soil profiles down to 1 m depth, with physico-chemical, elemental, and radiocarbon-dating analyses. The estimated mean soil organic carbon (SOC) storage in the upper meter of soils in the NE Greenland site is 8.3 ± 1.8 kg C m-2 compared to 20.3 ± 2.2 kg C m-2 and 30.0 ± 2.0 kg C m-2 in the NE Siberian sites (95% confidence intervals). The lower SOC storage in the High Arctic site in NE Greenland can be largely explained by the fact that 59% of the study area is located at higher elevation with mostly barren ground and thus very low SOC contents. In addition, SOC-rich fens and bogs occupy a much smaller proportion of the landscape in NE Greenland (∼3%) than in NE Siberia (∼20%). The contribution of deeper buried C-enriched material in the mineral soil horizons to the total SOC storage is lower in the NE Greenland site (∼13%) compared to the NE Siberian sites (∼24%–30%). Buried SOM seems generally more decomposed in NE Greenland than in NE Siberia, which we relate to different burial mechanisms prevailing in these regions.

  • 48.
    Palmtag, Juri
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ramage, Justine
    Stockholm University, Faculty of Science, Department of Physical Geography. Helmholtz Centre for Polar and Marine Research, Germany.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gentsch, Norman
    Lashchinskiy, Nikolay
    Richter, Andreas
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Controls on the storage of organic carbon in permafrost soil in northern Siberia2016In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 67, no 4, p. 478-491Article in journal (Refereed)
    Abstract [en]

    This research examined soil organic carbon (SOC), total nitrogen (TN) and aboveground phytomass carbon(PhC) stocks in two areas of the Taymyr Peninsula, northern Siberia.We combined field sampling, chemical and14C radiocarbon dating analyses with land cover classifications for landscape-level assessments. The estimatedmean for the 0–100-cm depth SOC stocks was 14.8 and 20.8 kgCm−2 in Ary-Mas and Logata, respectively. Thecorresponding values for TN were 1.0 and 1.3 kgNm−2. On average, about 2% only (range 0–12%) of the totalecosystem C is stored in PhC. In both study areas about 34% of the SOC at 0–100 cm is stored in cryoturbatedpockets, which have formed since at least the early Holocene. The larger carbon/nitrogen (C/N) ratio of thiscryoturbated material indicates that it consists of relatively undecomposed soil organic matter (SOM). Thereare substantial differences in SOC stocks and SOM properties within and between the two study areas, whichemphasizes the need to consider both geomorphology and soil texture in the assessment of landscape-level andregional SOC stocks.

    Highlights

    • This research addresses landscape-scale and regional variation in SOC stocks.

    • Landform and soil texture are taken into account in the analysis.

    • The contribution of phytomass to total ecosystem C stored is limited.

    • Large SOC stocks are susceptible to decomposition following permafrost thaw.

  • 49.
    Pastukhov, Alexander
    et al.
    Komi Science Centre.
    Kaverin, Kaverin
    Komi Science Centre.
    Mazhitova, Galina
    Komi Science Centre.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Shaktarova, Olga
    Komi Science Centre.
    Soil organic carbon storage in the forest-tundra ecotone zone in the North-Eastern Europe2011In: Geophysical Research Abstracts Vol. 13, EGU2011-53, 2011, 2011Conference paper (Other academic)
    Abstract [en]

    High latitude terrestrial ecosystems are considered key components in the global carbon (C) cycle [McGuire et al.,2009, Hugelius et al., 2010, in press]. Large stocks of soil organic carbon (SOC) have accumulated in Cryosolsand Histosols, where permafrost affects to reduce decomposition rates. In a recent study based on the NorthernCircumpolar Soil Carbon Database (3530 pedons, soil map mean polygon size 259 km2), Tarnocai et al. [2009]estimated soil organic carbon (SOC) stocks in the northern permafrost region to be 1024 Pg (Pg = g x 1015) forthe upper three meters (with Histosols contributing 278 Pg and Cryosols 634 Pg).This study describes detailed partitioning of soil organic carbon (SOC) for the forest-tundra ecotone zone in theborder of the discontinuous and massive island permafrost terrain with MAGT -0.5 to -2.0 C, North-EasternEuropean Russia.Soil cover of the study area is diverse and mosaic and form complexes of soils owing to a variety of microrelief,cryoturbation processes, snow cover distribution, etc. In peat plateau/thermokarst complexes, Cryic Folic Histosolswith shallow permafrost tables are interspersed with Fibric Histosols (permafrost free fens) and Fibric FloaticHistosols (thermokarst lakes in-filling with vegetation). Permafrost-affected mineral soils (Cryosols) are usuallyformed on loamy wind-exposed surfaces under tundra dwarf-shrub vegetation where shallow snow cover preservespermafrost within the soil profile. In these sites, quite thick peaty layers (10-40 cm) also favours shallow permafrostoccurrence (Histic Cryosols). Non-permafrost soils (Gleysols, Cambisols and Albeluvisols) are usually formed insites under tall shrub vegetation where thicker snow cover in winter results in a warmer soil regime. Non-permafrostsoils are developed under forest vegetation (Cambisols and Albeluvisols) and in floodplains (Fluvisols).Georeferenced soil data from field observations were overlaid on Landsat images and a supervised classificationprocedure was carried out. As a result satellite images were coded to raster maps containing soil type informationin pixel classes. The images were then homogenized prior to conversion to vector polygons. Resulting vector mapswere processed as shape files in the software ArcGIS 9.1, where adjacent uniform polygons were merged andcorrected and soil maps were compiled.Mean SOC storage (kg C m-2) for each soil type (SOC only) was calculated as the arithmetic mean of C storagein the sites belonging to that class and was upscale to soil groups in the map.Mean SOC storage for all four study areas combined is estimated to be 39.5 kg C m-2 (soil map and LCC upscalingrespectively). Detailed GIS map of SOC storage can be used to model the potential effect of permafrost thaw onSOC stores.

  • 50. Routh, Joyanto
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Filley, Timothy
    Tillman, Päivi Kaislahti
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Umea University.
    Becher, Marina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Multi-proxy study of soil organic matter dynamics in permafrost peat deposits reveal vulnerability to climate change in the European Russian Arctic2014In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 368, p. 104-117Article in journal (Refereed)
    Abstract [en]

    Soil organic carbon (SOC) in permafrost terrain is vulnerable to climate change. Perennially frozen peat deposits store large amounts of SOC, but we know little about its chemical composition and lability. We used plant macrofossil and biomarker analyses to reconstruct the Holocene paleovegetation and paleoenvironmental changes in two peat plateau profiles from the European Russian Arctic. Peat plateaus are the main stores of permafrost soil C in the region, but during most of the Holocene peats developed as permafrost-free rich fens with woody vegetation, sedges and mosses. Around 2200 cal BP, permafrost aggraded at the site resulting in frost heave and a drastic reduction in peat accumulation under the drier uplifted surface conditions. The permafrost dynamics (aggradation, frost-heave and thaw) ushered changes in plant assemblages and carbon accumulation, and consequently in the biomarker trends too. Detailed biomarker analyses indicate abundant neutral lipids, which follow the general pattern: n-alkanols > sterols >= n-alkanes >= triterpenols. The lignin monomers are not as abundant as the lipids and increase with depth. The selected aliphatic and phenolic compounds are source specific, and they have different degrees of lability, which is useful for tracing the impact of permafrost dynamics (peat accumulation and/or decay associated with thawing). However, common interpretation of biomarker patterns, and perceived hydrological and climate changes, must be applied carefully in permafrost regions. The increased proportion (selective preservation) of n-alkanes and lignin is a robust indicator of cumulative decomposition trajectories, which is mirrored by functional compounds (e. g. n-alkanol, triterpenol, and sterol concentrations) showing opposite trends. The distribution of these compounds follows first order decay kinetics, and concurs with the down core diagenetic changes. In particular, some of the biomarker ratios (e. g. stanol/sterol and higher plant alkane index) seem promising for tracing SOC decomposition despite changes in botanical imprint, and sites spanning across different soil types and locations. Carbon accumulation rate calculated at these sites varies from 18.1 to 31.1 gC m(-2) yr(-1), and it's evident selective preservation, molecular complexity of organic compounds, and freezing conditions enhance the long-term stability of SOC. Further, our results suggest that permafrost dynamics strongly impact the more undecomposed SOC that could be rapidly remobilized through ongoing thermokarst expansion.

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