title: Widespread methane seepage along the continental margin off Svalbard - from Bjørnøya to Kongsfjorden.
abstract: Numerous articles have recently reported on gas seepage offshore Svalbard, because the gas emission from these Arctic sediments was thought to result from gas hydrate dissociation, possibly triggered by anthropogenic ocean warming. We report on findings of a much broader seepage area, extending from 74° to 79°, where more than a thousand gas discharge sites were imaged as acoustic flares. The gas discharge occurs in water depths at and shallower than the upper edge of the gas hydrate stability zone and generates a dissolved methane plume that is hundreds of kilometer in length. Data collected in the summer of 2015 revealed that 0.02-7.7% of the dissolved methane was aerobically oxidized by microbes and a minor fraction (0.07%) was transferred to the atmosphere during periods of low wind speeds. Most flares were detected in the vicinity of the Hornsund Fracture Zone, leading us to postulate that the gas ascends along this fracture zone. The methane discharges on bathymetric highs characterized by sonic hard grounds, whereas glaciomarine and Holocene sediments in the troughs apparently limit seepage. The large scale seepage reported here is not caused by anthropogenic warming.
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Mau
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Römer
authors.affiliation: College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean Admin Building, Corvallis, Oregon 97331-5503, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Torres
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Bussmann
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Pape
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Damm
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Geprägs
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Wintersteller
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: C-W
authors.initials: CW
authors.lastname: Hsu
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Loher
authors.affiliation: MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Bohrmann