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  • 1. Chang, Kuang -Yu
    et al.
    Riley, William J.
    Crill, Patrick M.
    Grant, Robert F.
    Rich, Virginia I.
    Saleska, Scott R.
    Large carbon cycle sensitivities to climate across a permafrost thaw gradient in subarctic Sweden2019In: The Cryosphere, Vol. 13, no 2, p. 647-663Article in journal (Refereed)
    Abstract [en]

    Permafrost peatlands store large amounts of carbon potentially vulnerable to decomposition. However, the fate of that carbon in a changing climate remains uncertain in models due to complex interactions among hydrological, biogeochemical, microbial, and plant processes. In this study, we estimated effects of climate forcing biases present in global climate reanalysis products on carbon cycle predictions at a thawing permafrost peatland in subarctic Sweden. The analysis was conducted with a comprehensive biogeochemical model (ecosys) across a permafrost thaw gradient encompassing intact permafrost palsa with an ice core and a shallow active layer, partly thawed bog with a deeper active layer and a variable water table, and fen with a water table close to the surface, each with distinct vegetation and microbiota. Using in situ observations to correct local cold and wet biases found in the Global Soil Wetness Project Phase 3 (GSWP3) climate reanalysis forcing, we demonstrate good model performance by comparing predicted and observed carbon dioxide (CO2) and methane (CH4) exchanges, thaw depth, and water table depth. The simulations driven by the bias-corrected climate suggest that the three peatland types currently accumulate carbon from the atmosphere, although the bog and fen sites can have annual positive radiative forcing impacts due to their higher CH4 emissions. Our simulations indicate that projected precipitation increases could accelerate CH4 emissions from the palsa area, even without further degradation of palsa permafrost. The GSWP3 cold and wet biases for this site significantly alter simulation results and lead to erroneous active layer depth (ALD) and carbon budget estimates. Biases in simulated CO2 and CH4 exchanges from biased climate forcing are as large as those among the thaw stages themselves at a landscape scale across the examined permafrost thaw gradient. Future studies should thus not only focus on changes in carbon budget associated with morphological changes in thawing permafrost, but also recognize the effects of climate forcing uncertainty on carbon cycling.

  • 2. Fofana, Aminata
    et al.
    Anderson, Darya
    McCalley, Carmody K.
    Hodgkins, Suzanne
    Wilson, Rachel M.
    Cronin, Dylan
    Raab, Nicole
    Torabi, Mohammad
    Varner, Ruth K.
    Crill, Patrick
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Saleska, Scott R.
    Chanton, Jeffrey P.
    Tfaily, Malak M.
    Rich, Virginia I.
    Mapping substrate use across a permafrost thaw gradient2022In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 175, article id 108809Article in journal (Refereed)
    Abstract [en]

    Permafrost thaw in northern peatlands is likely to create a positive feedback to climate change, as microbes transform soil carbon (C) into carbon dioxide (CO2) or methane (CH4). While the microbiome's encoded C-processing potential changes with thaw, the impact on substrate utilization and gas emissions is less well characterized. We therefore examined microbial C-cycling dynamics from a partially thawed Sphagnum-dominated bog to a fully thawed sedge-dominated fen in Stordalen Mire (68.35°N, 19.05°E), Sweden. We profiled C substrate utilization diversity and extent by Biolog Ecoplates™, then tested substrate-specific hypotheses by targeted additions (of glucose, the short chain fatty acids (SCFAs) acetate and butyrate, and the organic acids galacturonic acid and p-hydroxybenzoic acid, all at field-relevant concentrations) under anaerobic conditions at 15 °C. In parallel we characterized microbiomes (via 16S rRNA amplicon sequencing and quantitative polymerase chain reaction) and C gas emissions. The fen exhibited a higher substrate use diversity and faster rate of overall substrate utilization than in the bog, based on Biolog Ecoplate™ incubations. Simple glucose additions (akin to a positive control) to peat microcosms fueled fermentation as expected (reflected in enriched fermenter lineages, their inferred metabolisms, and CO2 production), but also showed potential priming of anaerobic phenol degradation in the bog. Addition of SCFAs to bog and fen produced the least change in lineages and in CO2, and modest suppression of CH4 primarily in the fen, attributed to inhibition. Addition of both organic acids greatly increased the CO2:CH4 ratio in the deep peats but had distinct individual gas dynamics and impacts on microbiota. Both organic acids appeared to act as both C source and as a microbial inhibitor, with galacturonic acid also likely playing a role in electron transfer or acceptance. Collectively, these results support the importance of aboveground-belowground linkages - and in particular the role of Sphagnum spp.- in supplying substrates and inhibitors that drive microbiome assembly and C processing in these dynamically changing systems. In addition, they highlight an important temporal dynamic: responses on the short time scale of incubations (which would reflect transition conditions in the field) differ from those evident at the longer scales of habitat transition, in ways consequential to C gas emissions. In the short term, substrate addition response reflected microbiome legacy (e.g., bog communities were slower to process C and better tolerated inhibitors than fen communities) but led to little overall increase in C gas production (and a high skew to CO2). At the longer time scale of bog and fen thaw stages (which are used to represent these systems in models) the concomitant shifts in plants, hydrology and microbiota attenuate microbiome legacy impacts on substrate processing and C gas emissions over time. As habitat transition areas expand under accelerating change, we hypothesize an increased role of microbiome legacy in the landscape overall, leading to a lag in the increase of CH4 emissions expected from fen expansion.

  • 3. Holmes, M. E.
    et al.
    Crill, Patrick
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Burnett, W. C.
    McCalley, C. K.
    Wilson, R. M.
    Frolking, S.
    Chang, K-Y
    Riley, W. J.
    Varner, R. K.
    Hodgkins, S. B.
    McNichol, A. P.
    Saleska, S. R.
    Rich, V.
    Chanton, J. P.
    Carbon Accumulation, Flux, and Fate in Stordalen Mire, a Permafrost Peatland in Transition2022In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 36, no 1, article id e2021GB007113Article in journal (Refereed)
    Abstract [en]

    Stordalen Mire is a peatland in the discontinuous permafrost zone in arctic Sweden that exhibits a habitat gradient from permafrost palsa, to Sphagnum bog underlain by permafrost, to Eriophorum-dominated fully thawed fen. We used three independent approaches to evaluate the annual, multi-decadal, and millennial apparent carbon accumulation rates (aCAR) across this gradient: seven years of direct semi-continuous measurement of CO2 and CH4 exchange, and 21 core profiles for 210Pb and 14C peat dating. Year-round chamber measurements indicated net carbon balance of −13 ± 8, −49 ± 15, and −91 ± 43 g C m−2 y−1 for the years 2012–2018 in palsa, bog, and fen, respectively. Methane emission offset 2%, 7%, and 17% of the CO2 uptake rate across this gradient. Recent aCAR indicates higher C accumulation rates in surface peats in the palsa and bog compared to current CO2 fluxes, but these assessments are more similar in the fen. aCAR increased from low millennial-scale levels (17–29 g C m−2 y−1) to moderate aCAR of the past century (72–81 g C m−2 y−1) to higher recent aCAR of 90–147 g C m−2 y−1. Recent permafrost collapse, greater inundation and vegetation response has made the landscape a stronger CO2 sink, but this CO2 sink is increasingly offset by rising CH4 emissions, dominated by modern carbon as determined by 14C. The higher CH4 emissions result in higher net CO2-equivalent emissions, indicating that radiative forcing of this mire and similar permafrost ecosystems will exert a warming influence on future climate.

  • 4.
    Jansen, Joachim
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Thornton, Brett F.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Cortés, Alicia
    Snöälv, Jo
    Wik, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    MacIntyre, Sally
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Drivers of diffusive lake CH4 emissions on daily to multi-year time scales2020In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 17, no 7, p. 1911-1932Article in journal (Refereed)
    Abstract [en]

    Lakes and reservoirs are important emitters of climate forcing trace gases. Various environmental drivers of the flux, such as temperature and wind speed, have been identified, but their relative importance remains poorly understood. Here we use an extensive field dataset to disentangle physical and biogeochemical controls on the turbulence-driven diffusive flux of methane (CH4) on daily to multi-year timescales. We compare 8 years of floating chamber fluxes from three small, shallow subarctic lakes (2010–2017, n = 1306) with fluxes computed using 9 years of surface water concentration measurements (2009–2017, n = 606) and a small-eddy surface renewal model informed by in situ meteorological observations. Chamber fluxes averaged 6.9 ± 0.3 mg m−2 d−1 and gas transfer velocities (k600) from the chamber-calibrated surface renewal model averaged 4.0 ± 0.1 cm h−1. We find robust (R2 ≥ 0.93, p < 0.01) Arrhenius-type temperature functions of the CH4 flux (Ea' = 0.90 ± 0.14 eV) and of the surface CH4 concentration (Ea' = 0.88 ± 0.09 eV). Chamber derived gas transfer velocities tracked the power-law wind speed relation of the model (k ∝ u3/4). While the flux increased with wind speed, during storm events (U10 ≥ 6.5 m s−1) emissions were reduced by rapid water column degassing. Spectral analysis revealed that on timescales shorter than a month emissions were driven by wind shear, but on longer timescales variations in water temperature governed the flux, suggesting emissions were strongly coupled to production. Our findings suggest that accurate short- and long term projections of lake CH4 emissions can be based on distinct weather- and climate controlled drivers of the flux.

  • 5. Lakomiec, Patryk
    et al.
    Holst, Jutta
    Friborg, Thomas
    Crill, Patrick
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Rakos, Niklas
    Kljun, Natascha
    Olsson, Per-Ola
    Eklundh, Lars
    Persson, Andreas
    Rinne, Janne
    Field-scale CH4 emission at a subarctic mire with heterogeneous permafrost thaw status2021In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 18, no 20, p. 5811-5830Article in journal (Refereed)
    Abstract [en]

    The Arctic is exposed to even faster temperature changes than most other areas on Earth. Constantly increasing temperature will lead to thawing permafrost and changes in the methane (CH4) emissions from wetlands. One of the places exposed to those changes is the Abisko–Stordalen Mire in northern Sweden, where climate and vegetation studies have been conducted since the 1970s.

    In our study, we analyzed field-scale methane emissions measured by the eddy covariance method at Abisko–Stordalen Mire for 3 years (2014–2016). The site is a subarctic mire mosaic of palsas, thawing palsas, fully thawed fens, and open water bodies. A bimodal wind pattern prevalent at the site provides an ideal opportunity to measure mire patches with different permafrost status with one flux measurement system. The flux footprint for westerly winds was dominated by elevated palsa plateaus, while the footprint was almost equally distributed between palsas and thawing bog-like areas for easterly winds. As these patches are exposed to the same climatic and weather conditions, we analyzed the differences in the responses of their methane emission for environmental parameters.

    The methane fluxes followed a similar annual cycle over the 3 study years, with a gentle rise during spring and a decrease during autumn, without emission bursts at either end of the ice-free season. The peak emission during the ice-free season differed significantly for the two mire areas with different permafrost status: the palsa mire emitted 19 mg-C m−2 d−1 and the thawing wet sector 40 mg-C m−2 d−1. Factors controlling the methane emission were analyzed using generalized linear models. The main driver for methane fluxes was peat temperature for both wind sectors. Soil water content above the water table emerged as an explanatory variable for the 3 years for western sectors and the year 2016 in the eastern sector. The water table level showed a significant correlation with methane emission for the year 2016 as well. Gross primary production, however, did not show a significant correlation with methane emissions.

    Annual methane emissions were estimated based on four different gap-filing methods. The different methods generally resulted in very similar annual emissions. The mean annual emission based on all models was 3.1 ± 0.3 g-C m−2 a−1 for the western sector and 5.5 ± 0.5 g-C m−2 a−1 for the eastern sector. The average annual emissions, derived from these data and a footprint climatology, were 2.7 ± 0.5 and 8.2 ± 1.5 g-C m−2 a−1 for the palsa and thawing surfaces, respectively. Winter fluxes were relatively high, contributing 27 %–45 % to the annual emissions.

  • 6. 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
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    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.

  • 7.
    Stranne, Christian
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    O'Regan, Matthew
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Dickens, Gerald R.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Crill, Patrick
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Miller, C.
    Preto, Pedro
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Jakobsson, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Dynamic simulations of potential methane release from East Siberian continental slope sediments2016In: Geochemistry Geophysics Geosystems, E-ISSN 1525-2027, Vol. 17, no 3, p. 872-886Article in journal (Refereed)
    Abstract [en]

    Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of methane (CH4) in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 3 degrees C, and an assumed starting distribution of gas hydrate. The simulation results show that gas hydrate dissociation in these sediments is relatively slow, and that CH4 fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form in response to overpressure in pore space. With an initial gas hydrate distribution dictated by present-day pressure and temperature conditions, nominally 0.35 Gt of CH4 are released from the East Siberian slope during the first 100 years of the simulation. However, this CH4 discharge becomes significantly smaller (approximate to 0.05 Gt) if glacial sea level changes in the Arctic Ocean are considered. This is because a lower sea level during the last glacial maximum (LGM) must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. Even if all released CH4 reached the atmosphere, the amount coming from East Siberian slopes would be trivial compared to present-day atmospheric CH4 inputs from other sources.

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