Publication Date:
2021-06-09
Description:
Abstract We present a comprehensive study showing new results from a shallow gas seep area in
�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 �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 (�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 (SD5140), 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 �40 m water column, and furthermore provide an estimate of the emission rate needed to allow
for a contribution to the atmospheric methane concentration.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
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isiRev