NORWEGIAN JOURNAL OF GEOLOGY hps://dx.doi.org/10.17850/njg103-2-4 Gas seeps in Norwegian waters – distribution and mechanisms Terje Thorsnes 1,2* , Shyam Chand 1,2 , Valerie Bellec 1 , F. Chantel Nixon 3 , Harald Brunstad 4 , Aave Lepland 1 , Sigrun Melve Aarrestad 5 1 Geological Survey of Norway (NGU), P.O. Box 6315 Torgarden, 7491 Trondheim, Norway 2 CAGE – Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology, UiT the Arctic University of Norway, 9037 Tromsø, Norway 3 Department of Geography, Norwegian University of Science and Technology, P.O. Box 8900, 7491 Trondheim, Norway 4 Aker BP ASA, P.O. Box 65, NO-1324 Lysaker, Norway, Norway 5 Vestland fylkeskommune, P.O. Box 7900, 5020 Bergen, Norway Keywords: • Gas flares • Cold seeps • Carbonate crusts • Methane seepage • MAREANO Received: 30. September 2022 Accepted: 2. May 2023 Published online: 1. June 2023 Thorsnes, T., Chand, S., Bellec, V., Nixon, F.C., Brunstad, H., Lepland, A., & Aarrestad, S.M. 2023: Gas seeps in Norwegian waters – distribuon and mechanisms. Norwegian Journal of Geology 103, 202309. hps://dx.doi.org/10.17850/njg103-2-4 © Copyright the authors. This work is licensed under a Creave Commons Aribuon 4.0 Internaonal License. Gas seeps and fluid-flow related seabed features are found over the enre Norwegian exclusive economic zone (EEZ). Mulbeam water-column data from c. 136 000 km 2 has revealed more than 5 000 gas seeps. Most of the gas seeps seem to have biogenic, thermogenic or mixed origin; some may be of abioc origin. The spaal distribuon of the gas seeps appears to correlate with: 1 – structural highs with associated faulng, exposing hydrocarbon reservoir rocks at or near the seabed; 2 – faults serving as conduits for fluid flow; 3 – sengs where reservoir rocks overlain by less permeable cap rocks sub-crop at the seabed. Other mechanisms involve seepage around abandoned exploraon wells, and possible abioc gas generaon from serpennisaon of ultramafic rocks near mid-oceanic ridges. The gas seeping from the Norwegian cold seeps is mostly methane and has, in many places, led to the formaon of methane-derived authigenic carbonate crusts, which give evidence for either extensive gas seepage in the past or long-lived seepage. Chemosynthec communies are commonly associated with cold seeps and may form special habitats together with the carbonate crusts. Methane seepage has been proposed to contribute significantly to the global carbon budget and may be associated with gas hydrates giving rise to potenal geohazards. Gas seeps have been idenfied and spaally mapped as acousc gas flares, using mulbeam echosounder systems, which have the ability to record reflecons from both the water column and the seabed. Water-column data have been recorded in the MAREANO seabed mapping program since 2010, covering an area of c. 262 000 km 2 , with a data volume in the order of 210 Tb. The observaons of extensive gas flares in the Norwegian EEZ are available to the scienfic community and other users through a dedicated MAREANO data and web access system. *E-mail corresponding author (Terje Thorsnes) terje.thorsnes@ngu.no Electronic supplement 1: Gas seeps