title: Constraints on oceanic methane emissions west of Svalbard from atmospheric in situ measurements and Lagrangian transport modeling.
abstract: Methane stored in seabed reservoirs such as methane hydrates can reach the atmosphere in the form of bubbles or dissolved in water. Hydrates could destabilize with rising temperature further increasing greenhouse gas emissions in a warming climate. To assess the impact of oceanic emissions from the area west of Svalbard, where methane hydrates are abundant, we used measurements collected with a research aircraft (Facility for Airborne Atmospheric Measurements) and a ship (Helmer Hansen) during the Summer 2014 and for Zeppelin Observatory for the full year. We present a model-supported analysis of the atmospheric CH4mixing ratios measured by the different platforms. To address uncertainty about where CH4emissions actually occur, we explored three scenarios: areas with known seeps, a hydrate stability model, and an ocean depth criterion. We then used a budget analysis and a Lagrangian particle dispersion model to compare measurements taken upwind and downwind of the potential CH4emission areas. We found small differences between the CH4mixing ratios measured upwind and downwind of the potential emission areas during the campaign. By taking into account measurement and sampling uncertainties and by determining the sensitivity of the measured mixing ratios to potential oceanic emissions, we provide upper limits for the CH4fluxes. The CH4flux during the campaign was small, with an upper limit of 2.5 nmol m-2s-1in the stability model scenario. The Zeppelin Observatory data for 2014 suggest CH4fluxes from the Svalbard continental platform below 0.2 Tg yr-1. All estimates are in the lower range of values previously reported.
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: I
authors.identifier: 0000-0002-0056-7897
authors.initials: I
authors.lastname: Pisso
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: C Lund
authors.identifier: 0000-0003-3587-5926
authors.initials: CL
authors.lastname: Myhre
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: S M
authors.initials: SM
authors.lastname: Platt
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: S
authors.initials: S
authors.lastname: Eckhardt
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: O
authors.initials: O
authors.lastname: Hermansen
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: N
authors.initials: N
authors.lastname: Schmidbauer
authors.affiliation: Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology UiT-The Arctic University of Norway Tromsø Norway.
authors.forename: J
authors.initials: J
authors.lastname: Mienert
authors.affiliation: Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology UiT-The Arctic University of Norway Tromsø Norway.
authors.forename: S
authors.identifier: 0000-0003-1118-1321
authors.initials: S
authors.lastname: Vadakkepuliyambatta
authors.affiliation: FAAM Natural Environment Research Council Cranfield UK.
authors.forename: S
authors.identifier: 0000-0002-0385-3952
authors.initials: S
authors.lastname: Bauguitte
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK.
authors.forename: J
authors.identifier: 0000-0002-8660-5136
authors.initials: J
authors.lastname: Pitt
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK.
authors.forename: G
authors.identifier: 0000-0002-7070-3620
authors.initials: G
authors.lastname: Allen
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK.
authors.forename: K N
authors.initials: KN
authors.lastname: Bower
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK.
authors.forename: S
authors.identifier: 0000-0002-0489-1723
authors.initials: S
authors.lastname: O'Shea
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK; National Centre for Atmospheric Science UK.
authors.forename: M W
authors.identifier: 0000-0002-4968-6088
authors.initials: MW
authors.lastname: Gallagher
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Percival
authors.affiliation: National Centre for Atmospheric Science UK; Department of Chemistry University of Cambridge Cambridge UK.
authors.forename: J
authors.identifier: 0000-0003-3629-9916
authors.initials: J
authors.lastname: Pyle
authors.affiliation: National Centre for Atmospheric Science UK; Department of Chemistry University of Cambridge Cambridge UK.
authors.forename: M
authors.identifier: 0000-0003-2062-6556
authors.initials: M
authors.lastname: Cain
authors.affiliation: NILU-Norwegian Institute for Air Research Kjeller Norway.
authors.forename: A
authors.identifier: 0000-0002-2524-5755
authors.initials: A
authors.lastname: Stohl
keywords: Arctic methane; Lagrangian transport; emission flux; hydrates; inversion