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  • 1.
    Lindgren, Amelie
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Extensive loss of past permafrost carbon but a net accumulation into present-day soils2018In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 560, no 7717, p. 219-+Article in journal (Refereed)
    Abstract [en]

    Atmospheric concentrations of carbon dioxide increased between the Last Glacial Maximum (LGM, around 21,000 years ago) and the preindustrial era(1). It is thought that the evolution of this atmospheric carbon dioxide (and that of atmospheric methane) during the glacial-to-interglacial transition was influenced by organic carbon that was stored in permafrost during the LGM and then underwent decomposition and release following thaw(2,3). It has also been suggested that the rather erratic atmospheric delta C-13 and Delta C-14 signals seen during deglaciation(1.4) could partly be explained by the presence of a large terrestrial inert LGM carbon stock, despite the biosphere being less productive (and therefore storing less carbon)(5,6). Here we present an empirically derived estimate of the carbon stored in permafrost during the LGM by reconstructing the extent and carbon content of LGM biomes, peatland regions and deep sedimentary deposits. We find that the total estimated soil carbon stock for the LGM northern permafrost region is smaller than the estimated present-day storage (in both permafrost and non-permafrost soils) for the same region. A substantial decrease in the permafrost area from the LGM to the present day has been accompanied by a roughly 400-petagram increase in the total soil carbon stock. This increase in soil carbon suggests that permafrost carbon has made no net contribution to the atmospheric carbon pool since the LGM. However, our results also indicate potential postglacial reductions in the portion of the carbon stock that is trapped in permafrost, of around 1,000 petagrams, supporting earlier studies(7). We further find that carbon has shifted from being primarily stored in permafrost mineral soils and loess deposits during the LGM, to being roughly equally divided between peatlands, mineral soils and permafrost loess deposits today.

  • 2.
    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.

  • 3. Voigt, Carolina
    et al.
    Marushchak, Maija E.
    Lamprecht, Richard E.
    Jackowicz-Korczynski, Marcin
    Lindgren, Amelie
    Stockholm University, Faculty of Science, Department of Physical Geography. Lund University, Sweden.
    Mastepanov, Mikhail
    Granlund, Lars
    Christensen, Torben R.
    Tahvanainen, Teemu
    Martikainen, Pertti J.
    Biasi, Christina
    Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 24, p. 6238-6243Article in journal (Refereed)
    Abstract [en]

    Permafrost in the Arctic is thawing, exposing large carbon and nitrogen stocks for decomposition. Gaseous carbon release from Arctic soils due to permafrost thawing is known to be substantial, but growing evidence suggests that Arctic soils may also be relevant sources of nitrous oxide (N2O). Here we show that N2O emissions from subarctic peatlands increase as the permafrost thaws. In our study, the highest postthaw emissions occurred from bare peat surfaces, a typical landform in permafrost peatlands, where permafrost thaw caused a fivefold increase in emissions (0.56 +/- 0.11 vs. 2.81 +/- 0.6 mg N2O m(-2) d(-1)). These emission rates match those from tropical forest soils, the world's largest natural terrestrial N2O source. The presence of vegetation, known to limit N2O emissions in tundra, did decrease (by similar to 90%) but did not prevent thaw-induced N2O release, whereas waterlogged conditions suppressed the emissions. We show that regions with high probability for N2O emissions cover one-fourth of the Arctic. Our results imply that the Arctic N2O budget will depend strongly on moisture changes, and that a gradual deepening of the active layer will create a strong noncarbon climate change feedback.

  • 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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