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  • 1. Aben, Ralf C. H.
    et al.
    Barros, Nathan
    van Donk, Ellen
    Frenken, Thijs
    Hilt, Sabine
    Kazanjian, Garabet
    Lamers, Leon P. M.
    Peeters, Edwin T. H. M.
    Roelofs, Jan G. M.
    de Senerpont Domis, Lisette N.
    Stephan, Susanne
    Velthuis, Mandy
    Van de Waal, Dedmer B.
    Wik, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wilkinson, Jeremy
    DelSontro, Tonya
    Kosten, Sarian
    Cross continental increase in methane ebullition under climate change2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 1682Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) strongly contributes to observed global warming. As natural CH4 emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. Here we show a remarkably strong relationship between CH4 ebullition and temperature across a wide range of freshwater ecosystems on different continents using multi-seasonal CH4 ebullition data from the literature. As these temperature-ebullition relationships may have been affected by seasonal variation in organic matter availability, we also conducted a controlled year-round mesocosm experiment. Here 4 degrees C warming led to 51% higher total annual CH4 ebullition, while diffusion was not affected. Our combined findings suggest that global warming will strongly enhance freshwater CH4 emissions through a disproportional increase in ebullition (6-20% per 1 degrees C increase), contributing to global warming.

  • 2. Burdette, Shawn C.
    et al.
    Ball, Philip
    Day, Kat
    Scerri, Eric R.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Another four bricks in the wall2016In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 8, no 4, p. 283-288Article in journal (Other academic)
    Abstract [en]

    Of all the things humans can bestow names upon, new chemical elements are about the rarest. Our group of periodic table experts attempts to read the tea leaves and predict the names for elements 113, 115, 117 and 118.

  • 3.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Björk, Göran
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Andersson, Leif G.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor P.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Carbon cycling on the East Siberian Arctic Shelf – a change in air-sea CO2 flux induced by mineralization of terrestrial organic carbon2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189Article in journal (Refereed)
    Abstract [en]

    Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOCter and POCter) supplied to the shelf. Rivers supply on average 8.5 Tg C yr−1 dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr−1 DOCter and POCter respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ13CDOC) in shelf waters, we estimate that only some 20 % of the riverine DOCter is labile. According to our model results, an additional supply of approximately 14 Tg C yr−1 eroded labile POCter is however required to describe the observed stable isotope values of DIC (δ13CDIC). Degradation of riverine DOCter and POCter results in a 1.8 Tg C yr−1 reduction in the uptake of atmospheric CO2, while degradation of eroded POCter results in an additional 10 Tg C yr−1 reduction. Our calculations indicate nevertheless that the ESAS is an overall small net sink for atmospheric CO2 (1.7 Tg C yr−1). The external carbon sources are largely compensated by a net export from the shelf to the Arctic Ocean (31 Tg C yr−1), and to a smaller degree by a permanent burial in the sediments (2.7 Tg C yr−1).

  • 4.
    Horst, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Andersson, August
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Carrizo, Daniel
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Compound-specific bromine isotope analysis of methyl bromide using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry2011In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 25, no 17, p. 2425-2432Article in journal (Refereed)
    Abstract [en]

    Methyl bromide is the most important natural bromine contributor to stratospheric ozone depletion, yet there are still large uncertainties regarding quantification of its sources and sinks. The stable bromine isotope composition of CH(3)Br is potentially a powerful tool to apportion its sources and to study both its transport and its reactive fate. A novel compound-specific method to measure (81)Br/(79)Br isotope ratios in CH3Br using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry (GC/MCICPMS) was developed. Sample amounts of >40 ng could bemeasured with a precision of 0.1 parts per thousand (1 sigma, n=3). The method results are reproducible over the long term as shown with 36 analyses acquired over 3 months, yielding a standard deviation ( 1s) better than 0.4 parts per thousand. This new method demonstrates for the first time Br isotope ratio determination in gaseous brominated samples. It is three orders of magnitude more sensitive than previously existing isotope ratio mass spectrometry methods for Br isotope determination of other organobromines, thus allowing applications towards ambient atmospheric samples.

  • 5.
    Horst, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wishkerman, Asher
    Keppler, Frank
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Stable bromine isotopic composition of methyl bromide released from plant matter2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 125, p. 186-195Article in journal (Refereed)
    Abstract [en]

    Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (delta Br-81) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (epsilon) of -2.00 +/- 0.23 parts per thousand (1 sigma, n = 8) for pectin and -1.82 +/- 0.02 parts per thousand (1 sigma, n = 4) for Salicornia (the relative amount of the heavier Br-81 was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300 degrees C. For longer incubations of up to 90 h at 180 degrees C the delta Br-81 values increased from -2 parts per thousand to 0 parts per thousand for pectin and to -1 parts per thousand for Salicornia. These delta Br-81 source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget.

  • 6.
    Horst, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Laboratory for Isotope Geology, Swedish Museum of Natural History, Stockholm.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Stable bromine isotopic composition of atmospheric CH3BrArticle in journal (Refereed)
  • 7.
    Horst, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Stable bromine isotopic composition of atmospheric CH3Br2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, p. 21040-Article in journal (Refereed)
    Abstract [en]

    Tropospheric methyl bromide (CH3Br) is the largest source of bromine to the stratosphere and plays an important role in ozone depletion. Here, the first stable bromine isotope composition (delta Br-81) of atmospheric CH3Br is presented. The delta Br-81 of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of -0.04 +/- 0.28 parts per thousand ranging up to +1.75 +/- 0.12 parts per thousand. The Stockholm delta Br-81 versus concentration relationship corresponds to an apparent isotope enrichment factor of -4.7 +/- 3.7 parts per thousand, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric delta Br-81 measurements, which in the future may be combined with other isotope systems in a top-down inverse approach to further understand key source and sink processes of methyl bromide.

  • 8.
    Humborg, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Anderson, Leif G.
    Björk, Göran
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Bo
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Ek, Jörgen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor
    Sea-air exchange patterns along the central and outer East Siberian Arctic Shelf as inferred from continuous CO2, stable isotope, and bulk chemistry measurements2017In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 31, no 7, p. 1173-1191Article in journal (Refereed)
    Abstract [en]

    This large-scale quasi-synoptic study gives a comprehensive picture of sea-air CO2 fluxes during the melt season in the central and outer Laptev Sea (LS) and East Siberian Sea (ESS). During a 7 week cruise we compiled a continuous record of both surface water and air CO2 concentrations, in total 76,892 measurements. Overall, the central and outer parts of the ESAS constituted a sink for CO2, and we estimate a median uptake of 9.4 g C m(-2) yr(-1) or 6.6 Tg C yr(-1). Our results suggest that while the ESS and shelf break waters adjacent to the LS and ESS are net autotrophic systems, the LS is a net heterotrophic system. CO2 sea-air fluxes for the LS were 4.7 g C m(-2) yr(-1), and for the ESS we estimate an uptake of 7.2 g C m(-2) yr(-1). Isotopic composition of dissolved inorganic carbon (delta C-13(DIC) and delta C-13(CO2)) in the water column indicates that the LS is depleted in delta C-13(DIC) compared to the Arctic Ocean (ArcO) and ESS with an offset of 0.5% which can be explained by mixing of delta C-13(DIC)-depleted riverine waters and 4.0 Tg yr(-1) respiration of OCter; only a minor part (0.72 Tg yr(-1)) of this respired OCter is exchanged with the atmosphere. Property-mixing diagrams of total organic carbon and isotope ratio (delta C-13(SPE-DOC)) versus dissolved organic carbon (DOC) concentration diagram indicate conservative and nonconservative mixing in the LS and ESS, respectively. We suggest land-derived particulate organic carbon from coastal erosion as an additional significant source for the depleted delta C-13(DIC).

  • 9.
    Prytherch, John
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . University of Leeds, United Kingdom.
    Brooks, Ian
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thornton, Brett
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Salisbury, Dominic
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Anderson, Leif
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Air-sea CO2and CH4 gas transfer velocity in Arctic sea-ice regions fromeddy covariance flux measurements onboard Icebreaker Oden2017In: Geophysical Research Abstracts, ISSN 1029-7006, E-ISSN 1607-7962, Vol. 19, article id 697Article in journal (Refereed)
    Abstract [en]

    The Arctic Ocean is an important sink for atmospheric CO2, and there is ongoing debate on whether seafloor seeps in the Arctic are a large source of CH4 to the atmosphere. The impact of warming waters, decreasing sea-ice extent and expanding marginal ice zones on Arctic air-sea gas exchange depends on the rate of gas transfer in the presence of sea ice. Sea ice acts as a near-impermeable lid to air-sea gas exchange, but is also hypothesised to enhance gas transfer rates through physical processes such as increased surface-ocean turbulence from ice-water shear and ice-edge form drag. The dependence of the gas transfer rate on sea-ice concentration remains uncertain due to a lack of in situ measurements. Here we present the first direct estimates of gas transfer rate in a wide range of Arctic sea-ice conditions. The estimates were derived from eddy covariance CO2 and CH4 fluxes, measured from the Swedish Icebreaker Oden during two expeditions: the 3-month duration Arctic Clouds in Summer Experiment (ACSE) in 2014, a component of the Swedish-Russian-US Arctic Ocean Investigation on Climate-Cryosphere-Carbon Interactions (SWERUS-C3) in the eastern Arctic Ocean shelf region; and the Arctic Ocean 2016 expedition to the high latitude Arctic Ocean. Initial CO2 results from ACSE showed that the gas transfer rate has a near-linear dependence on sea-ice concentration, and that some previous indirect measurements and modelling estimates overestimate gas transfer rates in sea-ice regions. This supports a linear sea-ice scaling approach for assessments of polar ocean carbon fluxes. Air-sea gas transfer model assumptions (e.g. Schmidt number dependence) will be examined using simultaneous CO2 and CH4 measurements, and observations in different ice conditions (e.g. summer melt, autumn freeze up, central Arctic and marginal ice zones) will be compared.

  • 10.
    Prytherch, John
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . University of Leeds, UK.
    Brooks, Ian M.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Salisbury, Dominic J.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Anderson, Leif G.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Direct determination of the air-sea CO2 gas transfer velocity in Arctic sea ice regions2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 8, p. 3770-3778Article in journal (Refereed)
    Abstract [en]

    The Arctic Ocean is an important sink for atmospheric CO2. The impact of decreasing sea ice extent and expanding marginal ice zones on Arctic air-sea CO2 exchange depends on the rate of gas transfer in the presence of sea ice. Sea ice acts to limit air-sea gas exchange by reducing contact between air and water but is also hypothesized to enhance gas transfer rates across surrounding open-water surfaces through physical processes such as increased surface-ocean turbulence from ice-water shear and ice-edge form drag. Here we present the first direct determination of the CO2 air-sea gas transfer velocity in a wide range of Arctic sea ice conditions. We show that the gas transfer velocity increases near linearly with decreasing sea ice concentration. We also show that previous modeling approaches overestimate gas transfer rates in sea ice regions.

  • 11. Saunois, M.
    et al.
    Bousquet, P.
    Poulter, B.
    Peregon, A.
    Ciais, P.
    Canadell, J. G.
    Dlugokencky, E. J.
    Etiope, G.
    Bastviken, D.
    Houweling, S.
    Janssens-Maenhout, G.
    Tubiello, F. N.
    Castaldi, S.
    Jackson, R. B.
    Alexe, M.
    Arora, V. K.
    Beerling, D. J.
    Bergamaschi, P.
    Blake, D. R.
    Brailsford, G.
    Brovkin, V.
    Bruhwiler, L.
    Crevoisier, C.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Covey, K.
    Curry, C.
    Frankenberg, C.
    Gedney, N.
    Höglund-Isaksson, L.
    Ishizawa, M.
    Ito, A.
    Joos, F.
    Kim, H. -S
    Kleinen, T.
    Krummel, P.
    Lamarque, J. -F
    Langenfelds, R.
    Locatelli, R.
    Machida, T.
    Maksyutov, S.
    McDonald, K. C.
    Marshall, J.
    Melton, J. R.
    Morino, I.
    Naik, V.
    O'Doherty, S.
    Parmentier, F. -JW.
    Patra, P. K.
    Peng, C.
    Peng, S.
    Peters, G. P.
    Pison, I.
    Prigent, C.
    Prinn, R.
    Ramonet, M.
    Riley, W. J.
    Saito, M.
    Santini, M.
    Schroeder, R.
    Simpson, I. J.
    Spahni, R.
    Steele, P.
    Takizawa, A.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tian, H.
    Tohjima, Y.
    Viovy, N.
    Voulgarakis, A.
    van Weele, M.
    van der Werf, G. R.
    Weiss, R.
    Wiedinmyer, C.
    Wilton, D. J.
    Wiltshire, A.
    Worthy, D.
    Wunch, D.
    Xu, X.
    Yoshida, Y.
    Zhang, B.
    Zhang, Z.
    Zhu, Q.
    The global methane budget 2000–20122016In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 8, no 2, p. 697-751Article, review/survey (Refereed)
    Abstract [en]

    The global methane (CH4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH4 over the past decade. Emissions and concentrations of CH4 are continuing to increase, making CH4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH4 sources that overlap geographically, and from the destruction of CH4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (∼ biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories and data-driven approaches (including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). For the 2003–2012 decade, global methane emissions are estimated by top-down inversions at 558 Tg CH4 yr−1, range 540–568. About 60 % of global emissions are anthropogenic (range 50–65 %). Since 2010, the bottom-up global emission inventories have been closer to methane emissions in the most carbon-intensive Representative Concentrations Pathway (RCP8.5) and higher than all other RCP scenarios. Bottom-up approaches suggest larger global emissions (736 Tg CH4 yr−1, range 596–884) mostly because of larger natural emissions from individual sources such as inland waters, natural wetlands and geological sources. Considering the atmospheric constraints on the top-down budget, it is likely that some of the individual emissions reported by the bottom-up approaches are overestimated, leading to too large global emissions. Latitudinal data from top-down emissions indicate a predominance of tropical emissions (∼ 64 % of the global budget, < 30° N) as compared to mid (∼ 32 %, 30–60° N) and high northern latitudes (∼ 4 %, 60–90° N). Top-down inversions consistently infer lower emissions in China (∼ 58 Tg CH4 yr−1, range 51–72, −14 %) and higher emissions in Africa (86 Tg CH4 yr−1, range 73–108, +19 %) than bottom-up values used as prior estimates. Overall, uncertainties for anthropogenic emissions appear smaller than those from natural sources, and the uncertainties on source categories appear larger for top-down inversions than for bottom-up inventories and models. The most important source of uncertainty on the methane budget is attributable to emissions from wetland and other inland waters. We show that the wetland extent could contribute 30–40 % on the estimated range for wetland emissions. Other priorities for improving the methane budget include the following: (i) the development of process-based models for inland-water emissions, (ii) the intensification of methane observations at local scale (flux measurements) to constrain bottom-up land surface models, and at regional scale (surface networks and satellites) to constrain top-down inversions, (iii) improvements in the estimation of atmospheric loss by OH, and (iv) improvements of the transport models integrated in top-down inversions. The data presented here can be downloaded from the Carbon Dioxide Information Analysis Center (http://doi.org/10.3334/CDIAC/GLOBAL_METHANE_BUDGET_2016_V1.1) and the Global Carbon Project.

  • 12. Saunois, M.
    et al.
    Bousquet, P.
    Poulter, B.
    Peregon, A.
    Ciais, P.
    Canadell, J. G.
    Dlugokencky, E. J.
    Etiope, G.
    Bastviken, D.
    Houweling, S.
    Janssens-Maenhout, G.
    Tubiello, F. N.
    Castaldi, S.
    Jackson, R. B.
    Alexe, M.
    Arora, V. K.
    Beerling, D. J.
    Bergamaschi, P.
    Blake, D. R.
    Brailsford, G.
    Bruhwiler, L.
    Crevoisier, C.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Covey, K.
    Frankenberg, C.
    Gedney, N.
    Höglund-Isaksson, L.
    Ishizawa, M.
    Ito, A.
    Joos, F.
    Kim, H. -S
    Kleinen, T.
    Krummel, P.
    Lamarque, J. -F
    Langenfelds, R.
    Locatelli, R.
    Machida, T.
    Maksyutov, S.
    Melton, J. R.
    Morino, I.
    Naik, V.
    O'Doherty, S.
    Parmentier, F. -JW.
    Patra, P. K.
    Peng, C.
    Peng, S.
    Peters, G. P.
    Pison, I.
    Prinn, R.
    Ramonet, M.
    Riley, W. J.
    Saito, M.
    Santini, M.
    Schroeder, R.
    Simpson, I. J.
    Spahni, R.
    Takizawa, A.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tian, H.
    Tohjima, Y.
    Viovy, N.
    Voulgarakis, A.
    Weiss, R.
    Wilton, D. J.
    Wiltshire, A.
    Worthy, D.
    Wunch, D.
    Xu, X.
    Yoshida, Y.
    Zhang, B.
    Zhang, Z.
    Zhu, Q.
    Variability and quasi-decadal changes in the methane budget over the period 2000–20122017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 18, p. 11135-11161Article in journal (Refereed)
    Abstract [en]

    Following the recent Global Carbon Project (GCP) synthesis of the decadal methane (CH4) budget over 2000–2012 (Saunois et al., 2016), we analyse here the same dataset with a focus on quasi-decadal and inter-annual variability in CH4 emissions. The GCP dataset integrates results from top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models (including process-based models for estimating land surface emissions and atmospheric chemistry), inventories of anthropogenic emissions, and data-driven approaches. The annual global methane emissions from top-down studies, which by construction match the observed methane growth rate within their uncertainties, all show an increase in total methane emissions over the period 2000–2012, but this increase is not linear over the 13 years. Despite differences between individual studies, the mean emission anomaly of the top-down ensemble shows no significant trend in total methane emissions over the period 2000–2006, during the plateau of atmospheric methane mole fractions, and also over the period 2008–2012, during the renewed atmospheric methane increase. However, the top-down ensemble mean produces an emission shift between 2006 and 2008, leading to 22 [16–32] Tg CH4 yr−1 higher methane emissions over the period 2008–2012 compared to 2002–2006. This emission increase mostly originated from the tropics, with a smaller contribution from mid-latitudes and no significant change from boreal regions. The regional contributions remain uncertain in top-down studies. Tropical South America and South and East Asia seem to contribute the most to the emission increase in the tropics. However, these two regions have only limited atmospheric measurements and remain therefore poorly constrained. The sectorial partitioning of this emission increase between the periods 2002–2006 and 2008–2012 differs from one atmospheric inversion study to another. However, all top-down studies suggest smaller changes in fossil fuel emissions (from oil, gas, and coal industries) compared to the mean of the bottom-up inventories included in this study. This difference is partly driven by a smaller emission change in China from the top-down studies compared to the estimate in the Emission Database for Global Atmospheric Research (EDGARv4.2) inventory, which should be revised to smaller values in a near future. We apply isotopic signatures to the emission changes estimated for individual studies based on five emission sectors and find that for six individual top-down studies (out of eight) the average isotopic signature of the emission changes is not consistent with the observed change in atmospheric 13CH4. However, the partitioning in emission change derived from the ensemble mean is consistent with this isotopic constraint. At the global scale, the top-down ensemble mean suggests that the dominant contribution to the resumed atmospheric CH4 growth after 2006 comes from microbial sources (more from agriculture and waste sectors than from natural wetlands), with an uncertain but smaller contribution from fossil CH4 emissions. In addition, a decrease in biomass burning emissions (in agreement with the biomass burning emission databases) makes the balance of sources consistent with atmospheric 13CH4 observations. In most of the top-down studies included here, OH concentrations are considered constant over the years (seasonal variations but without any inter-annual variability). As a result, the methane loss (in particular through OH oxidation) varies mainly through the change in methane concentrations and not its oxidants. For these reasons, changes in the methane loss could not be properly investigated in this study, although it may play a significant role in the recent atmospheric methane changes as briefly discussed at the end of the paper.

  • 13. Thonat, T.
    et al.
    Saunois, M.
    Bousquet, P.
    Pison, I.
    Tan, Z.
    Zhuang, Q.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, D.
    Dlugokencky, E. J.
    Zimov, N.
    Laurila, T.
    Hatakka, J.
    Hermansen, O.
    Worthy, D. E. J.
    Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 13, p. 8371-8394Article in journal (Refereed)
    Abstract [en]

    Understanding the recent evolution of methane emissions in the Arctic is necessary to interpret the global methane cycle. Emissions are affected by significant uncertainties and are sensitive to climate change, leading to potential feedbacks. A polar version of the CHIMERE chemistry-transport model is used to simulate the evolution of tropospheric methane in the Arctic during 2012, including all known regional anthropogenic and natural sources, in particular freshwater emissions which are often overlooked in methane modelling. CHIMERE simulations are compared to atmospheric continuous observations at six measurement sites in the Arctic region. In winter, the Arctic is dominated by anthropogenic emissions; emissions from continental seepages and oceans, including from the East Siberian Arctic Shelf, can contribute significantly in more limited areas. In summer, emissions from wetland and freshwater sources dominate across the whole region. The model is able to reproduce the seasonality and synoptic variations of methane measured at the different sites. We find that all methane sources significantly affect the measurements at all stations at least at the synoptic scale, except for biomass burning. In particular, freshwater systems play a decisive part in summer, representing on average between 11 and 26 % of the simulated Arctic methane signal at the sites. This indicates the relevance of continuous observations to gain a mechanistic understanding of Arctic methane sources. Sensitivity tests reveal that the choice of the land-surface model used to prescribe wetland emissions can be critical in correctly representing methane mixing ratios. The closest agreement with the observations is reached when using the two wetland models which have emissions peaking in August–September, while all others reach their maximum in June–July. Such phasing provides an interesting constraint on wetland models which still have large uncertainties at present. Also testing different freshwater emission inventories leads to large differences in modelled methane. Attempts to include methane sinks (OH oxidation and soil uptake) reduced the model bias relative to observed atmospheric methane. The study illustrates how multiple sources, having different spatiotemporal dynamics and magnitudes, jointly influence the overall Arctic methane budget, and highlights ways towards further improved assessments.

  • 14. Thonat, Thibaud
    et al.
    Saunois, Marielle
    Pison, Isabelle
    Berchet, Antoine
    Hocking, Thomas
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bousquet, Philippe
    Assessment of the theoretical limit in instrumental detectability of northern high-latitude methane sources using delta C-13(CH4) atmospheric signals2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 19, p. 12141-12161Article in journal (Refereed)
    Abstract [en]

    Recent efforts have brought together bottom-up quantification approaches (inventories and process-based models) and top-down approaches using regional observations of methane atmospheric concentrations through inverse modelling to better estimate the northern high-latitude methane sources. Nevertheless, for both approaches, the relatively small number of available observations in northern high-latitude regions leaves gaps in our understanding of the drivers and distributions of the different types of regional methane sources. Observations of methane isotope ratios, performed with instruments that are becoming increasingly affordable and accurate, could bring new insights on the contributions of methane sources and sinks. Here, we present the source signal that could be observed from methane isotopic (CH4)-C-13 measurements if high-resolution observations were available and thus what requirements should be fulfilled in future instrument deployments in terms of accuracy in order to constrain different emission categories. This theoretical study uses the regional chemistry-transport model CHIMERE driven by different scenarios of isotopic signatures for each regional methane source mix. It is found that if the current network of methane monitoring sites were equipped with instruments measuring the isotopic signal continuously, only sites that are significantly influenced by emission sources could differentiate regional emissions with a reasonable level of confidence. For example, wetland emissions require daily accuracies lower than 0.2 parts per thousand for most of the sites. Detecting East Siberian Arctic Shelf (ESAS) emissions requires accuracies lower than 0.05 parts per thousand at coastal Russian sites (even lower for other sites). Freshwater emissions would be detectable with an uncertainty lower than 0.1 parts per thousand for most continental sites. Except Yakutsk, Siberian sites require stringent uncertainty (lower than 0.05 parts per thousand) to detect anthropogenic emissions from oil and gas or coal production. Remote sites such as Zeppelin, Summit, or Alert require a daily uncertainty below 0.05 parts per thousand to detect any regional sources. These limits vary with the hypothesis on isotopic signatures assigned to the different sources.

  • 15.
    Thornton, Brett
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn
    Worcester Polytechnic Institute.
    Homely holmium2015In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 7, no 6, p. 532-532Article in journal (Other academic)
    Abstract [en]

    Brett F. Thornton and Shawn C. Burdette consider holmium's hotly contested discovery and later obscurity.

  • 16.
    Thornton, Brett
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Microbial lid on subsea methane2015In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 5, p. 723-724Article in journal (Refereed)
    Abstract [en]

    Submarine permafrost thaw in the Arctic has been suggested as a trigger for the release of large quantities of methane to the water column, and subsequently the atmosphere - with important implications for global warming. Now research shows that microbial oxidation of methane at the thaw front can effectively prevent its release.

  • 17.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    Chemistry’s Decision Point: Isotopes2017In: Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications / [ed] Mark A. Benvenuto, Tracy Williamson, American Chemical Society (ACS), 2017, p. 119-140Chapter in book (Refereed)
    Abstract [en]

    Although the modern periodic table barely resembles the one constructed by Dmitri Mendeleev, every chemistry student learns that the placement of missing elements in the open slots of Mendeleev’s table was a scientific triumph. The discovery of isotopes in the early 1900s was an inflection point in periodicity, and chemistry as a discipline. Chemists once characterized each new isotope as a unique element—but as isotopes proliferated, fitting them into the existing periodic table became impossible. Several decades passed before the concept of isotopy fully developed. At that point, scientists seemingly concluded that chemistry occurred at the atomic level, and isotopic differences were the purview of physics. Had a different understanding of isotopy prevailed, the direction of chemistry could have changed dramatically. While the trajectory of synthetic chemistry might have remained constant, ‘chemists’ may have dominated the discovery of new superheavy elements by appropriating the modern conventional definition of ‘nuclear physicist’.

  • 18.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Burdette, Shawn C.
    University of Connecticut.
    Finding eka-iodine: discovery priority in modern times2010In: Bulletin for the History of Chemistry, ISSN 1053-4385, Vol. 35, no 2, p. 86-96Article in journal (Refereed)
  • 19.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    Frantically forging fermium2017In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 9, p. 724-724Article in journal (Other academic)
    Abstract [en]

    Brett F. Thornton and Shawn C. Burdette relate how element 100 was first identified in a nuclear weapons test, but that was classified information, so researchers had to ‘discover’ it again using other methods.

  • 20.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    Nobelium non-believers2014In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 6, p. 652-652Article in journal (Other academic)
  • 21.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    Worcester Polytechnic Institute.
    Recalling radon's recognition2013In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 5, no 9, p. 804-Article in journal (Other academic)
  • 22.
    Thornton, Brett F
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C
    Worcester Polytechnic Institute.
    The ends of elements2013In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 5, no 5, p. 350-352Article in journal (Other academic)
  • 23.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    The neodymium neologism2017In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 9, p. 194-194Article in journal (Other academic)
    Abstract [en]

    From grand challenges of nineteenth century chemistry to powerful technology in small packages, Brett F. Thornton and Shawn C. Burdette explain why neodymium is the twin element discovered twice by two Carls.

  • 24.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    Worcester Polytechnic Institute.
    The straight dope on isotopes2013In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 5, p. 979-981Article in journal (Other academic)
  • 25.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Burdette, Shawn C.
    Worcester Polytechnic Institute.
    Up for Discussion: Naming Superheavy Halogen and Noble Elements2013In: Chemistry International, ISSN 0193-6484, E-ISSN 1365-2192, Vol. 35, no 6, p. 26-27Article in journal (Other (popular science, discussion, etc.))
  • 26.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Methane fluxes from the sea to the atmosphere across the Siberian shelf seas2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 11, p. 5869-5877Article in journal (Refereed)
    Abstract [en]

    The Laptev and East Siberian Seas have been proposed as a substantial source of methane (CH4) to the atmosphere. During summer 2014, we made unique high-resolution simultaneous measurements of CH4 in the atmosphere above, and surface waters of, the Laptev and East Siberian Seas. Turbulence-driven sea-air fluxes along the ship's track were derived from these observations; an average diffusive flux of 2.99mgm(-2) d(-1) was calculated for the Laptev Sea and for the ice-free portions of the western East Siberian Sea, 3.80mgm(-2)d(-1). Although seafloor bubble plumes were observed at two locations in the study area, our calculations suggest that regionally, turbulence-driven diffusive flux alone accounts for the observed atmospheric CH4 enhancements, with only a local, limited role for bubble fluxes, in contrast to earlier reports. CH4 in subice seawater in certain areas suggests that a short-lived flux also occurs annually at ice-out.

  • 27.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Horst, Axel
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Carrizo, Daniel
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Methyl chloride and methyl bromide emissions from baking: an unrecognized anthropogenic source2016In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 551, p. 327-333Article in journal (Refereed)
    Abstract [en]

    Methyl chloride and methyl bromide (CH3Cl and CH3Br) are the largest natural sources of chlorine and bromine, respectively, to the stratosphere, where they contribute to ozone depletion. We report the anthropogenic production of CH3Cl and CH3Br during breadbaking, and suggest this production is an abiotic process involving the methyl ester functional groups in pectin and lignin structural polymers of plant cells. Wide variations in baking styles allow only rough estimates of this flux of methyl halides on a global basis. A simple model suggests that CH3Br emissions from breadbaking likely peaked circa 1990 at approximately 200 tonnes per year (about 0.3% of industrial production), prior to restrictions on the dough conditioner potassium bromate. In contrast, CH3Cl emissions from breadbaking may be of similar magnitude as acknowledged present-day CH3Cl industrial emissions. Because the mechanisms involve functional groups and compounds widely found in plant materials, this type of methyl halide production may occur in other cooking techniques as well.

  • 28.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Horst, Axel
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Carrizo, Daniel
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    A High-Volume Cryosampler and Sample Purification System for Bromine Isotope Studies of Methyl Bromide2013In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 30, no 9, p. 2095-2107Article in journal (Refereed)
    Abstract [en]

    A system was developed for collecting from the ambient atmosphere the methyl halides CH3Cl and CH3Br in quantities sufficient for chlorine and bromine isotope analysis. The construction and operation of the novel cryogenic collection system (cryosampler) and sample purification system developed for this task are described. This study demonstrates the capability of the cryosampler by quantifying the CH3Cl and CH3Br collected from atmospheric samples and the nonfractionating bromine isotope fingerprint of CH3Br from synthetic air samples of controlled composition. An optimized cryosampler operation time of 4 h at a flow rate of 15 L min(-1) is applied to yield the nearly 40 ng required for subsequent Br-81-CH3Br analyses. The sample purification system is designed around a packed column gas chromatography-quadropole-mass spectrometry (GCqMS) system with three additional cryotraps and backflushing capacity. The system's suitability was tested by observing both the mass recovery and the lack of Br-81 isotope fractionation induced during sample purification under varying flow rates and loading scenarios. To demonstrate that the entire system samples and dependably delivers CH3Br to the isotope analysis system without inducing isotope fractionation, diluted synthetic air mixtures prepared from standard gases were processed through the entire system, yielding a Br-81-CH3Br of +0.03 parts per thousand +/- 0.10 parts per thousand relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever Br-81-CH3Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding -0.08 parts per thousand +/- 0.43 parts per thousand and +1.75 parts per thousand +/- 0.13 parts per thousand versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site.

  • 29.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wik, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Climate-forced changes in available energy and methane bubbling from subarctic lakes2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 6, p. 1936-1942Article in journal (Refereed)
    Abstract [en]

    Strong correlations between seasonal energy input and methane (CH4) bubbling (ebullition) in northern lakes suggest that energy proxies might provide a constraint on the magnitude of future CH4 emissions. Ebullition is a major pathway for transporting anaerobically produced CH4 from lake sediments to the atmosphere and represents a large unquantified CH4 source. In high-latitude, postglacial lakes during the ice-free season, solar shortwave energy input can constrain CH4 productivity via control of sediment temperature. Utilizing long-term climatic predictors, we calculate CH4 ebullition from three subarctic lakes in northern Sweden over the period of 1916-2079. Using observed energy trends, the seasonal average lake CH4 ebullition is predicted to increase by 80% between the 1916-1926 decade and the 2040-2079 period. Present-day seasonal average methane ebullition is estimated to have already increased 24% since the 1916-1926 decade.

  • 30.
    Thornton, Brett F.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wik, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Double-counting challenges the accuracy of high-latitude methane inventories2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 24, p. 12,569-12,577Article in journal (Refereed)
    Abstract [en]

    Quantification of the present and future contribution to atmospheric methane (CH4) from lakes, wetlands, fluvial systems, and, potentially, coastal waters remains an important unfinished task for balancing the global CH4 budget. Discriminating between these sources is crucial, especially across climate-sensitive Arctic and subarctic landscapes and waters. Yet basic underlying uncertainties remain, in such areas as total wetland area and definitions of wetlands, which can lead to conflation of wetlands and small ponds in regional studies. We discuss how in situ sampling choices, remote sensing limitations, and isotopic signature overlaps can lead to unintentional double-counting of CH4 emissions and proposethat this double-counting can explain a pan-Arctic bottom-up estimate from published sources, 59.7 Tg yr-1(range 36.9–89.4 Tg yr-1) greatly exceeding the most recent top-down inverse modeled estimate of thepan-Arctic CH4 budget (235 Tg yr-1).

  • 31.
    Wik, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    MacIntyre, Sally
    Varner, Ruth K.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Energy input is primary controller of methane bubbling in subarctic lakes2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 2, p. 555-560Article in journal (Refereed)
    Abstract [en]

    Emission of methane (CH4) from surface waters is often dominated by ebullition (bubbling), a transport mode with high-spatiotemporal variability. Based on new and extensive CH4 ebullition data, we demonstrate striking correlations (r(2) between 0.92 and 0.997) when comparing seasonal bubble CH4 flux from three shallow subarctic lakes to four readily measurable proxies of incoming energy flux and daily flux magnitudes to surface sediment temperature (r(2) between 0.86 and 0.94). Our results after continuous multiyear sampling suggest that CH4 ebullition is a predictable process, and that heat flux into the lakes is the dominant driver of gas production and release. Future changes in the energy received by lakes and ponds due to shorter ice-covered seasons will predictably alter the ebullitive CH4 flux from freshwater systems across northern landscapes. This finding is critical for our understanding of the dynamics of radiatively important trace gas sources and associated climate feedback.

  • 32.
    Wik, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Uhlbäck, Jo
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Biased sampling of methane release from northern lakes: A problem for extrapolation2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 3, p. 1256-1262Article in journal (Refereed)
    Abstract [en]

    Methane emissions from lakes are widely thought to be highly irregular and difficult to quantify with anything other than numerous distributed measurement stations and long-term sampling campaigns. In spite of this, a large majority of the study sites north of 50°N have been measured over surprisingly short time periods of only one to a few days. Using long-term data from three intensively studied small subarctic lakes, we recommend that measurements of diffusive methane flux and ebullition should be made over at least 11 and 39 days scattered throughout the ice-free season using depth-stratified sampling at 3 and 11 or more locations, respectively. We further show that low temporal and spatial resolutions are unlikely to cause overestimates. Therefore, we argue that most sites measured previously are likely underestimated in terms of emission potential. Avoiding these biases seen in much of the contemporary data is crucial to further constrain large-scale methane emissions from northern lakes and ponds.

  • 33.
    Wik, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Varner, Ruth K.
    Thornton, Brett
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    McCalley, Carmody
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Large isotopic variations and similarities in methane ebullition from northern lakesManuscript (preprint) (Other academic)
    Abstract [en]

    Lakes are abundant in northern, high latitude landscapes and considered a substantial source of atmospheric methane (CH4). In spite of this, little is known about how CH4 release mechanisms relate to underlying organic sources and biogenic production pathways in different types of water bodies. Here, we present a substantial, multiyear dataset of the stable isotopes of CH4 ebullition from three interconnected, subarctic post-glacial lakes. The δ13C-CH4 and δD-CH4 vary from -78.4 to -53.1‰ and from -369.8 to -218.8‰, respectively. Overall, these observations suggest predominantly acetoclastic methanogenesis in the shallow zones, possibly fueled by in-situ plant production, and a shift towards a mix with hydrogenotrophy at depth. The bubbles’ δ13C-CH4 are similar to most of those reported from other northern natural systems, but we found differences in δD-CH4, possibly due to evaporation-driven fractionation over summer. Stable isotopes provide valuable information about underlying organic sources and production pathways, however, due to large overlaps they may not be effective in reducing uncertainties in emissions potentials among different water body types, and in general between lakes and wetlands.

1 - 33 of 33
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