Methane-flow system within the Nyegga pockmark field, offshore mid-Norway

Type Article
Date 2023-10
Language English
Author(s) Dupré StéphanieORCID1, Foucher Jean-Paul1, Pierre Catherine2, Decker Carole3, Westbrook Graham4, Ker StephanORCID1, Olu - Le Roy KarineORCID3, Donval Jean-Pierre1, Charlou Jean-Luc1, Blanc-Valleron Marie-Madeleine5, Nouze Herve1
Affiliation(s) 1 : UMR GEO-OCEAN, IFREMER, Plouzané, France
2 : UMR LOCEAN, Sorbonne Université, Paris, France
3 : UMR BEEP, IFREMER, Plouzané, France
4 : School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
5 : UMR-CR2P, CNRS-MNHN, Paris, France
Source Frontiers In Earth Science (2296-6463) (Frontiers Media SA), 2023-10 , Vol. 11 , P. 1250619 (24p.)
DOI 10.3389/feart.2023.1250619
Keyword(s) Norwegian margin, gas chimneys, pockmarks, seeps, authigenic carbonates, chemosynthesis-based communities, gas hydrate, dissolved methane

We investigated fluid seepage within the Nyegga pockmark field (600–900 m water depths) off mid-Norway from Remotely Operated Vehicle dives at the so-called CNE sites (CNE01 to CNE17). The seafloor morphology of some of these features corresponds to pockmarks and adjacent ridges, with the latter being the focus of present seepage activity. These structures are underlain by chimneys above a gas-charged zone with, in some cases, a substantial body of hydrate-invaded sediment (down to 1.3 s in two-way travel time at CNE03). Present-day methane-rich fluid seepage through the seabed is indicated by chemosynthetic fauna, in particular Siboglinidae polychaetes (Oligobrachia haakonmobiensis webbi and Sclerolinum contortum), microbial mats and associated Rissoidae gastropod (Alvania sp.) grazers, and confirmed by measured in situ bottom-water methane anomalies, up to 2,130 nL/L. No free-gas bubble emissions were observed or acoustically identified. The presence of authigenic carbonates reveals past seepage with very low δ13C values (down to −58‰) indicating that the major source of carbon was methane carried by the venting fluids. The ages of major periods of methane venting are provided by vesicomyid bivalve shells (Isorropodon nyeggaensis) present in two sedimentary layers, 14,930 and 15,500 14C yr BP (ca. 17,238 and 17,952 cal yr BP), respectively, corresponding to the time of Melt Water Pulse IA. The seafloor morphology and pattern of seepage -chemosynthetic fauna and microbial mat distribution and dissolved methane concentration-are remarkably heterogeneous. Pore-water chemistry profiles in a gravity core taken only 40 m from major seepage sites indicate no seepage and anaerobic methane oxidation at a sub-bottom depth of about 2 m. Present-day seepage from the studied pockmark-chimney fluid-flow system charged with gas hydrate is dominated by the advection of methane solution in pore water. Some of this methane could result from the dissolution of hydrate in the chimney, most of which would have formed during an earlier period (post-LGM times) of history of the chimney, when it was venting free gas. However, the presence of free gas beneath this chimney is probably why the water entering the chimney is already saturated with methane and the process of hydrate formation in the chimney continues today.

Full Text
File Pages Size Access
Publisher's official version 24 9 MB Open access
Supplementary Material 3 MB Open access
Top of the page

How to cite 

Dupré Stéphanie, Foucher Jean-Paul, Pierre Catherine, Decker Carole, Westbrook Graham, Ker Stephan, Olu - Le Roy Karine, Donval Jean-Pierre, Charlou Jean-Luc, Blanc-Valleron Marie-Madeleine, Nouze Herve (2023). Methane-flow system within the Nyegga pockmark field, offshore mid-Norway. Frontiers In Earth Science, 11, 1250619 (24p.). Publisher's official version : , Open Access version :