Assessing marine gas emission activity and contribution to the atmospheric methane inventory: A multidisciplinary approach from the Dutch Dogger Bank seep area (North Sea).

Römer, M., Wenau, S., Mau, Susan, Veloso, Mario, Greinert, Jens , Schlüter, Michael and Bohrmann, Gerhard (2017) Assessing marine gas emission activity and contribution to the atmospheric methane inventory: A multidisciplinary approach from the Dutch Dogger Bank seep area (North Sea). Open Access Geochemistry, Geophysics, Geosystems, 18 (7). pp. 2617-2633. DOI 10.1002/2017GC006995.

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Abstract

We present a comprehensive study showing new results from a shallow gas seep area in approximate to 40 m water depth located in the North Sea, Netherlands sector B13 that we call Dutch Dogger Bank seep area. It has been postulated that methane presumably originating from a gas reservoir in approximate to 600 m depth below the seafloor is naturally leaking to the seafloor. Our ship-based subbottom echosounder data indicate that the migrating gas is trapped in numerous gas pockets in the shallow sediments. The gas pockets are located at the boundary between the top of the Late Pliocene section and overlying fine-grained sediments, which were deposited during the early Holocene marine transgression after the last glaciation. We mapped gas emissions during three R/V Heincke cruises in 2014, 2015, and 2016 and repeatedly observed up to 850 flares in the study area. Most of them (approximate to 80%) were concentrated at five flare clusters. Our repeated analysis revealed spatial similarities of seep clusters, but also heterogeneities in emission intensities. A first calculation of the methane released from these clusters into the water column revealed a flow rate of 277 L/min (SD=140), with two clusters emitting 132 and 142 L/min representing the most significant seepage sites. Above these two flare clusters, elevated methane concentrations were recorded in atmospheric measurements. Our results illustrate the effective transport of methane via gas bubbles through a approximate to 40 m water column, and furthermore provide an estimate of the emission rate needed to allow for a contribution to the atmospheric methane concentration.

Document Type: Article
Additional Information: Data acquired for this study are available through the World Data Center PANGAEA.
Keywords: methane bubble emission; flare cluster; subseafloor gas accumulation; atmospheric CH4 input; Dogger Bank
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems > DeepSea Monitoring
AWI
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1002/2017GC006995
ISSN: 1525-2027
Projects: IMGAM, Excellence Cluster 'The Ocean in the Earth System'
Contribution Number:
ProjectNumber
DSM30
Expeditions/Models/Experiments:
Date Deposited: 04 Sep 2017 11:49
Last Modified: 01 Feb 2019 15:07
URI: http://oceanrep.geomar.de/id/eprint/39243

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