| 81. |
- Sannel, Britta, et al.
(författare)
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Long-term stability of permafrost in subarctic peat plateaus, west-central Canada
- 2008
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 18:4, s. 589-601
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Tidskriftsartikel (refereegranskat)abstract
- Long-term vegetation succession and permafrost dynamics in subarctic peat plateaus of west-central Canada have been studied through detailed plant macrofossil analysis and extensive AMS radiocarbon dating of two peat profiles. Peatland inception at these sites occurred around 5800-5100 yr BP (6600-5900 cal. BP) as a result of paludification of upland forests. At the northern peat plateau site, located in the continuous permafrost zone, palaeobotanical evidence suggests that permafrost was already present under the forested upland prior to peatland development. Paludification was initiated by permafrost collapse, but re-aggradation of permafrost occurred soon after peatland inception. At the southern site, located in the discontinuous permafrost zone, the aggradation of permafrost occurred soon after peatland inception. In the peat plateaus, permafrost conditions have remained very stable until present. Sphagnum fuscum-dominated stages have alternated with more xerophytic communities characterized by ericaceous shrubs. Local peat fires have occurred, but most of these did not cause degradation of the permafrost. Starting from 2800-1100 yr BP (2900-1000 cal. BP) consistently dry surface conditions have prevailed, possibly related to continued frost heave or nearby polygon crack formation.
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| 82. |
- Schuur, E. A. G., et al.
(författare)
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Climate change and the permafrost carbon feedback
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 520:7546, s. 171-179
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Forskningsöversikt (refereegranskat)abstract
- Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. Awarming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.
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| 83. |
- Schuur, E. A. G., et al.
(författare)
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Expert assessment of vulnerability of permafrost carbon to climate change
- 2013
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 119:2, s. 359-374
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Tidskriftsartikel (refereegranskat)abstract
- Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19-45 Pg C by 2040, 162-288 Pg C by 2100, and 381-616 Pg C by 2300 in CO2 equivalent using 100-year CH4 global warming potential (GWP). These values become 50 % larger using 20-year CH4 GWP, with a third to a half of expected climate forcing coming from CH4 even though CH4 was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing.
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| 84. |
- Shala, Shyhrete, et al.
(författare)
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Evaluating environmental drivers of Holocene changes in water chemistry and aquatic biota composition at Lake Loitsana, NE Finland
- 2014
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 52:4, s. 311-329
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry C-14 dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies.
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| 85. |
- Siewert, Matthias B., et al.
(författare)
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Comparing carbon storage of Siberian tundra and taiga permafrost ecosystems at very high spatial resolution
- 2015
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 120:10, s. 1973-1994
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost-affected ecosystems are important components in the global carbon (C) cycle that, despite being vulnerable to disturbances under climate change, remain poorly understood. This study investigates ecosystem carbon storage in two contrasting continuous permafrost areas of NE and East Siberia. Detailed partitioning of soil organic carbon (SOC) and phytomass carbon (PC) is analyzed for one tundra (Kytalyk) and one taiga (Spasskaya Pad/Neleger) study area. In total, 57 individual field sites (24 and 33 in the respective areas) have been sampled for PC and SOC, including the upper permafrost. Landscape partitioning of ecosystem C storage was derived from thematic upscaling of field observations using a land cover classification from very high resolution (2x2m) satellite imagery. Nonmetric multidimensional scaling was used to explore patterns in C distribution. In both environments the ecosystem C is mostly stored in the soil (86%). At the landscape scale C stocks are primarily controlled by the presence of thermokarst depressions (alases). In the tundra landscape, site-scale variability of C is controlled by periglacial geomorphological features, while in the taiga, local differences in catenary position, soil texture, and forest successions are more important. Very high resolution remote sensing is highly beneficial to the quantification of C storage. Detailed knowledge of ecosystem C storage and ground ice distribution is needed to predict permafrost landscape vulnerability to projected climatic changes. We argue that vegetation dynamics are unlikely to offset mineralization of thawed permafrost C and that landscape-scale reworking of SOC represents the largest potential changes to C cycling.
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| 86. |
- Siewert, Matthias Benjamin, 1985-
(författare)
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High-resolution mapping and spatial variability of soil organic carbon storage in permafrost environments
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large amounts of carbon are stored in soils of the northern circumpolar permafrost region. High-resolution mapping of this soil organic carbon (SOC) is important to better understand and predict local to global scale carbon dynamics. In this thesis, studies from five different areas across the permafrost region indicate a pattern of generally higher SOC storage in Arctic tundra soils compared to forested sub-Arctic or Boreal taiga soils. However, much of the SOC stored in the top meter of tundra soils is permanently frozen, while the annually thawing active layer is deeper in taiga soils and more SOC may be available for turnover to ecosystem processes. The results show that significantly more carbon is stored in soils compared to vegetation, even in fully forested taiga ecosystems. This indicates that over longer timescales, the SOC potentially released from thawing permafrost cannot be offset by a greening of the Arctic. For all study areas, the SOC distribution is strongly influenced by the geomorphology, i.e. periglacial landforms and processes, at different spatial scales. These span from the cryoturbation of soil horizons, to the formation of palsas, peat plateaus and different generations of ice-wedges, to thermokarst creating kilometer scale macro environments. In study areas that have not been affected by Pleistocene glaciation, SOC distribution is highly influenced by the occurrence of ice-rich and relief-forming Yedoma deposits. This thesis investigates the use of thematic maps from highly resolved satellite imagery (<6.5 m resolution). These maps reveal important information on the local distribution and variability of SOC, but their creation requires advanced classification methods including an object-based approach, modern classifiers and data-fusion. The results of statistical analyses show a clear link of land cover and geomorphology with SOC storage. Peat-formation and cryoturbation are identified as two major mechanisms to accumulate SOC. As an alternative to thematic maps, this thesis demonstrates the advantages of digital soil mapping of SOC in permafrost areas using machine-learning methods, such as support vector machines, artificial neural networks and random forests. Overall, high-resolution satellite imagery and robust spatial prediction methods allow detailed maps of SOC. This thesis significantly increases the amount of soil pedons available for the individual study areas. Yet, this information is still the limiting factor to better understand the SOC distribution in permafrost environments at local and circumpolar scale. Soil pedon information for SOC quantification should at least distinguish the surface organic layer, the mineral subsoil in the active layer compared to the permafrost and further into organic rich cryoturbated and buried soil horizons.
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| 87. |
- Sjöberg, Ylva, et al.
(författare)
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Thermokarst Lake Morphometry and Erosion Features in Two Peat Plateau Areas of Northeast European Russia
- 2013
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 24:1, s. 75-81
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution satellite remote sensing analysis (n=637 lakes) and field measurements (n=29 lakes) of two peat plateau areas in northeast European Russia were carried out to investigate lake morphology, map shoreline erosion indicators and assess possible orientation patterns in lake and shore morphology. The study includes the first detailed characterisation of the shape and size of thermokarst lakes in organic terrain. The area covered by lakes is 7.0 per cent and 13.6 per cent, and median lake size is 184m2 and 265m2, respectively, for the two study areas. In both areas, most lakes have a similar northwest to southeast orientation, and shores most commonly face northeast or southwest. The shores are generally steeper and have more cracks and lake depths are greater along shores facing northeast or southeast, and along the shorelines of larger lakes. Shores with a peat substrate are more heterogeneous than those with a mineral substrate in terms of steepness, cracks and water depths. Since the lakes are generally small, the shoreline/area ratio is high and a large part of the peat plateau areas can potentially be affected by shoreline erosion.
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| 88. |
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| 89. |
- Tesi, Tommaso, et al.
(författare)
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Composition and fate of terrigenous organic matter along the Arctic land-ocean continuum in East Siberia : Insights from biomarkers and carbon isotopes
- 2014
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 133, s. 235-256
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming is predicted to translocate terrigenous organic carbon (TerrOC) to the Arctic Ocean and affect the marine biogeochemistry at high latitudes. The magnitude of this translocation is currently unknown, so is the climate response. The fate of the remobilized TerrOC across the Arctic shelves represents an unconstrained component of this feedback. The present study investigated the fate of permafrost carbon along the land-ocean continuum by characterizing the TerrOC composition in three different terrestrial carbon pools from Siberian permafrost (surface organic rich horizon, mineral soil active layer, and Ice Complex deposit) and marine sediments collected on the extensive East Siberian Arctic Shelf (ESAS). High levels of lignin phenols and cutin acids were measured in all terrestrial samples analyzed indicating that these compounds can be used to trace the heterogeneous terrigenous material entering the Arctic Ocean. In ESAS sediments, comparison of these terrigenous biomarkers with other TerrOC proxies (bulk delta C-13/delta C-14 and HMW lipid biomarkers) highlighted contrasting across-shelf trends. These differences could indicate that TerrOC in the ESAS is made up of several pools that exhibit contrasting reactivity toward oxidation during the transport. In this reactive spectrum, lignin is the most reactive, decreasing up to three orders of magnitude from the inner-to the outer-shelf while the decrease of HMW wax lipid biomarkers was considerably less pronounced. Alternatively, degradation might be negligible while sediment sorting during the across-shelf transport could be the major physical forcing that redistributes different TerrOC pools characterized by different matrix-association. Despite the marked decrease shown by lignin, the fingerprint of lignin phenols such as the acid: aldehyde ratio of vanillyl and syringyl phenols showed a lack of any across-shelf trends and exhibited an extremely wide range of values in all terrestrial samples. By contrast, the 3,5-dihydroxybenzoic: vanillyl phenols ratio exhibited a clear across-shelf trend suggesting either increasing degradation with distance from the coast or TerrOC sorting along the sediment dispersal system. The ratio of syringyl: vanillyl phenols indicated that gymnosperm tissues are more important than angiosperm tissues in surface sediments, in particular off the Lena River mouth, consistent with the vegetation in its watershed. Conversely, the fingerprint of p-hydroxybenzenes suggests lack of substantial input of moss-derived material. Finally, autochthonous lipid-and protein-derived CuO reaction products displayed a strong along-shelf gradient likely reflecting the inflow of nutrient-rich Pacific waters from the Bering Strait that stimulate primary productivity in the eastern ESAS. In particular short-chain fatty acids showed a clear frontal/transition zone between Pacific-influenced and river-influenced waters approximately along the 160 degrees E longitude. Considering the labile nature of phytoplankton, priming and co-metabolism processes might stimulate degradation of TerrOC in the easternmost region of the Siberian shelf. This study demonstrated the need to consider multiple TerrOC proxies at isotopic/molecular levels to differentiate the fate for different allocthonous components in Arctic sediments and the need to assess how these TerrOC pools are distributed in different density, size, and settling fractions to better discriminate between the extent of hydrodynamic sorting versus degradation.
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| 90. |
- Treat, Claire C., et al.
(författare)
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Widespread global peatland establishment and persistence over the last 130,000 y
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116:11, s. 4822-4827
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Tidskriftsartikel (refereegranskat)abstract
- Glacial-interglacial variations in CO2 and methane in polar ice cores have been attributed, in part, to changes in global wetland extent, but the wetland distribution before the Last Glacial Maximum (LGM, 21 ka to 18 ka) remains virtually unknown. We present a study of global peatland extent and carbon (C) stocks through the last glacial cycle (130 ka to present) using a newly compiled database of 1,063 detailed stratigraphic records of peat deposits buried by mineral sediments, as well as a global peatland model. Quantitative agreement between modeling and observations shows extensive peat accumulation before the LGM in northern latitudes (> 40 degrees N), particularly during warmer periods including the last interglacial (130 ka to 116 ka, MIS 5e) and the interstadial (57 ka to 29 ka, MIS 3). During cooling periods of glacial advance and permafrost formation, the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent, thickness, and modeled C stocks by 70 to 90% from warmer times. Tropical peatland extent and C stocks show little temporal variation throughout the study period. While the increased burial of northern peats was correlated with cooling periods, the burial of tropical peat was predominately driven by changes in sea level and regional hydrology. Peat burial by mineral sediments represents a mechanism for long-term terrestrial C storage in the Earth system. These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene.
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