Preprints
https://doi.org/10.5194/os-2021-85
https://doi.org/10.5194/os-2021-85

  13 Sep 2021

13 Sep 2021

Review status: this preprint is currently under review for the journal OS.

Autonomous methane seep site monitoring offshore Western Svalbard: Hourly to seasonal variability and associated oceanographic parameters

Knut Ola Dølven1, Bénédicte Ferré1, Anna Silyakova1, Pär Jansson2, Peter Linke3,, and Manuel Moser1, Knut Ola Dølven et al.
  • 1Centre for Arctic Gas Hydrate, Environment, and Climate,UiT The Arctic University of Norway, 9019 Tromsø, Norway
  • 2Multiconsult Kyst og Marin, 9013 Tromsø, Norway
  • 3GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany
  • These authors contributed equally to this work.

Abstract. Improved quantification techniques of natural sources is needed to explain variations in atmospheric methane. In polar regions, high uncertainties in current estimates of methane release from the seabed remain. We present two unique 10 and 3 months long time-series of bottom water measurements of physical and chemical parameters from two autonomous ocean observatories deployed at separate intense seabed methane seep sites (91 and 246 m depth) offshore Western Svalbard from 2015 to 2016. Results show high short term (100–1000 nmol L-1 within hours) and seasonal variation, as well as higher (2–7 times) methane concentrations compared to previous measurements. Rapid variability is explained by uneven distribution of seepage and changing ocean current directions. No overt influence of tidal hydrostatic pressure or water temperature variations on methane concentration was observed, but an observed negative correlation with temperature at the 246 site fits with hypothesized seasonal blocking of lateral methane pathways in the sediments. Negative correlation between bottom water methane concentration/variability and wind forcing, concomitant with signs of weaker water column stratification, indicates increased potential for methane release to the atmosphere in fall/winter. We highlight uncertainties in methane inventory estimates based on discrete water sampling and present new information about short- and long-term methane variability which can help constrain future estimates of seabed methane seepage.

Knut Ola Dølven et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-85', Anonymous Referee #1, 14 Oct 2021
    • AC1: 'Reply on RC1', Knut Ola Dølven, 27 Oct 2021
  • RC2: 'Comment on os-2021-85', Anonymous Referee #2, 01 Nov 2021

Knut Ola Dølven et al.

Knut Ola Dølven et al.

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Short summary
Natural sources of atmospheric methane needs to be better described and quantified. We present time series from ocean observatories monitoring two seabed methane seep sites in the Arctic. Methane concentration varied considerably on short time scales and moderate on a seasonal scale. Seeps persisted throughout the year, with increased potential for atmospheric release in winter season due to water mixing. Results highlight uncertainties in current methane estimates from seabed methane seepage.