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  • 1.
    Horst, Axel
    et al.
    Stockholms universitet, Institutionen för tillämpad miljövetenskap (ITM).
    Thornton, Brett F.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Holmstrand, Henry
    Stockholms universitet, Institutionen för tillämpad miljövetenskap (ITM).
    Andersson, Per
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Gustafsson, Örjan
    Stockholms universitet, Institutionen för tillämpad miljövetenskap (ITM).
    Stable bromine isotopic composition of atmospheric CH3Br2013Inngår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, artikkel-id 21040Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    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 scales2020Inngår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 17, nr 7, s. 1911-1932Artikkel i tidsskrift (Fagfellevurdert)
    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.

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