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  • 1. Natali, Susan M.
    et al.
    Watts, Jennifer D.
    Rogers, Brendan M.
    Potter, Stefano
    Ludwig, Sarah M.
    Selbmann, Anne-Katrin
    Sullivan, Patrick F.
    Abbott, Benjamin W.
    Arndt, Kyle A.
    Birch, Leah
    Björkman, Mats P.
    Bloom, A. Anthony
    Celis, Gerardo
    Christensen, Torben R.
    Christiansen, Casper T.
    Commane, Roisin
    Cooper, Elisabeth J.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Czimczik, Claudia
    Davydov, Sergey
    Du, Jinyang
    Egan, Jocelyn E.
    Elberling, Bo
    Euskirchen, Eugenie S.
    Friborg, Thomas
    Genet, Hélène
    Göckede, Mathias
    Goodrich, Jordan P.
    Grogan, Paul
    Helbig, Manuel
    Jafarov, Elchin E.
    Jastrow, Julie D.
    Kalhori, Aram A. M.
    Kim, Yongwon
    Kimball, John S.
    Kutzbach, Lars
    Lara, Mark J.
    Larsen, Klaus S.
    Lee, Bang-Yong
    Liu, Zhihua
    Loranty, Michael M.
    Lund, Magnus
    Lupascu, Massimo
    Madani, Nima
    Malhotra, Avni
    Matamala, Roser
    McFarland, Jack
    McGuire, A. David
    Michelsen, Anders
    Minions, Christina
    Oechel, Walter C.
    Olefeldt, David
    Parmentier, Frans-Jan W.
    Pirk, Norbert
    Poulter, Ben
    Quinton, William
    Rezanezhad, Fereidoun
    Risk, David
    Sachs, Torsten
    Schaefer, Kevin
    Schmidt, Niels M.
    Schuur, Edward A. G.
    Semenchuk, Philipp R.
    Shaver, Gaius
    Sonnentag, Oliver
    Starr, Gregory
    Treat, Claire C.
    Waldrop, Mark P.
    Wang, Yihui
    Welker, Jeffrey
    Wille, Christian
    Xu, Xiaofeng
    Zhang, Zhen
    Zhuang, Qianlai
    Zona, Donatella
    Large loss of CO2 in winter observed across the northern permafrost region2019In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 9, no 11, p. 852-857Article in journal (Refereed)
    Abstract [en]

    Recent warming in the Arctic, which has been amplified during the winter(1-3), greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)(4). However, the amount of CO2 released in winter is not known and has not been well represented by ecosystem models or empirically based estimates(5,6). Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October-April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (-1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario-Representative Concentration Pathway 4.5-and 41% under business-as-usual emissions scenario-Representative Concentration Pathway 8.5. Our results provide a baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions.

  • 2. Treat, Claire C.
    et al.
    Kleinen, Thomas
    Broothaerts, Nils
    Dalton, April S.
    Dommain, Rene
    Douglas, Thomas A.
    Drexler, Judith Z.
    Finkelstein, Sarah A.
    Grosse, Guido
    Hope, Geoffrey
    Hutchings, Jack
    Jones, Miriam C.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lacourse, Terri
    Lahteenoja, Outi
    Loisel, Julie
    Notebaert, Bastiaan
    Payne, Richard J.
    Peteet, Dorothy M.
    Sannel, A. Britta K.
    Stelling, Jonathan M.
    Strauss, Jens
    Swindles, Graeme T.
    Talbot, Julie
    Tarnocai, Charles
    Verstraeten, Gert
    Williams, Christopher J.
    Xia, Zhengyu
    Yu, Zicheng
    Valiranta, Minna
    Hättestrand, Martina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Alexanderson, Helena
    Brovkin, Victor
    Widespread global peatland establishment and persistence over the last 130,000 y2019In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 11, p. 4822-4827Article in journal (Refereed)
    Abstract [en]

    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.

  • 3. Treat, Claire C.
    et al.
    Marushchak, Maija E.
    Voigt, Carolina
    Zhang, Yu
    Tan, Zeli
    Zhuang, Qianlai
    Virtanen, Tarmo A.
    Räsänen, Aleksi
    Biasi, Christina
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kaverin, Dmitry
    Miller, Paul A.
    Stendel, Martin
    Romanovsky, Vladimir
    Rivkin, Felix
    Martikainen, Pertti J.
    Shurpali, Narasinha J.
    Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 11, p. 5188-5204Article in journal (Refereed)
    Abstract [en]

    Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO2) and methane (CH4) fluxes for the dominant land cover types in a similar to 100-km(2) sub-Arctic tundra region in northeast European Russia for the period of 2006-2015 using process-based biogeochemical models. Modeled net annual CO2 fluxes ranged from --300 g C m(-2) year(-1) [net uptake] in a willow fen to 3 g Cm-2 year(-1) [net source] in dry lichen tundra. Modeled annual CH4 emissions ranged from -0.2 to 22.3 g Cm-2 year(-1) at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20%-25%) in comparison with variability among the land cover types (150%). Using high-resolution land cover classification, the region was a net sink of atmospheric CO2 across most land cover types but a net source of CH4 to the atmosphere due to high emissions from permafrost-free fens. Using a lower resolution for land cover classification resulted in a 20%-65% underestimation of regional CH4 flux relative to high-resolution classification and smaller (10%) overestimation of regional CO2 uptake due to the underestimation of wetland area by 60%. The relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites because wetlands were hot spots for C cycling in Arctic tundra ecosystems.

  • 4. Voigt, Carolina
    et al.
    Marushchak, Maija E.
    Mastepanov, Mikhail
    Lamprecht, Richard E.
    Christensen, Torben R.
    Dorodnikov, Maxim
    Jackowicz-Korczynski, Marcin
    Lindgren, Amelie
    Stockholm University, Faculty of Science, Department of Physical Geography. Lund University, Sweden.
    Lohila, Annalea
    Nykänen, Hannu
    Oinonen, Markku
    Oksanen, Timo
    Palonen, Vesa
    Treat, Claire C.
    Martikainen, Pertti J.
    Biasi, Christina
    Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw2019In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 25, no 5, p. 1746-1764Article in journal (Refereed)
    Abstract [en]

    Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long-term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time-span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant-soil systems (mesocosms) allowed us to simulate permafrost thaw under near-natural conditions. We monitored GHG flux dynamics via high-resolution flow-through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10-15 cm of permafrost under dry conditions increased CO2 emissions to the atmosphere (without vegetation: 0.74 +/- 0.49 vs. 0.84 +/- 0.60 g CO2-C m(-2) day(-1); with vegetation: 1.20 +/- 0.50 vs. 1.32 +/- 0.60 g CO2-C m(-2) day(-1), mean +/- SD, pre- and post-thaw, respectively). Radiocarbon dating (C-14) of respired CO2, supported by an independent curve-fitting approach, showed a clear contribution (9%-27%) of old carbon to this enhanced post-thaw CO2 flux. Elevated concentrations of CO2, CH4, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH4 in the peat column, however, prevented CH4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost-carbon feedback by adding to the atmospheric CO2 burden post-thaw. However, as long as the water table remains low, our results reveal a strong CH4 sink capacity in these types of Arctic ecosystems pre- and post-thaw, with the potential to compensate part of the permafrost CO2 losses over longer timescales.

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