A climatic trigger for the giant Troll pockmark field in the northern North Sea.

Mazzini, Adriano, Svensen, Henrik H., Forsberg, Carl Fredrik, Linge, Henriette, Lauritzen, Stein-Erik, Haflidason, Haflidi, Hammer, Øyvind, Planke, Sverre and Tjelta, Tor Inge (2017) A climatic trigger for the giant Troll pockmark field in the northern North Sea. Earth and Planetary Science Letters, 464 . pp. 24-34. DOI 10.1016/j.epsl.2017.02.014.

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Abstract

Pockmarks are seafloor craters usually formed during methane release on continental margins.
However, the mechanisms behind their formation and dynamics remain elusive. Here we ,report detailed investigations on one of ,the World’s largest pockmark fields located in the Troll region in the northern North Sea. Seafloor investigations show that >7000 pockmarks are present in a∼600 km2 area. A similar density of
pockmarks is likely present over a 15,000 km2
region outside our study area. Based on extensive monitoring, coring, geophysical and
geochemical analyses, no indications of active gas seepage were found. Still, geochemical data
from carbonate blocks collected from these pockmarks indicate a methanogenic origin linked
to gas hydrate dissociation and past fluid venting at the seafloor. We have dated the carbonates using the U–Th method in order to constrain the pockmark formation. The carbonates
gave an isochron age of 9.59±.38 ka, i.e. belonging to the initial Holocene. Moreover, radiocarbon dating of microfossils in the sediments inside the pockmarks is consistent with the ages derived from the carbonates. Based
on pressure and temperature modelling, we show that the last deglaciation could have triggered
dissociation of gas hydrates present in the region of the northern part of the Norwegian
Channel, causing degassing of 0.26 Mt CH4/km2 at
the seafloor. Our results stress the importance of external climatic forcing of the dynamics of
the seafloor, and the role of the rapid warming
following the Younger Dryas in pacing the marine
gas hydrate reservoir.

Document Type: Article
Keywords: Norwegian North Sea, Troll, pockmarks, gas, hydrates dissociation, deglaciation modelling
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.epsl.2017.02.014
ISSN: 0012-821X
Projects: FLOWS
Date Deposited: 02 May 2018 12:27
Last Modified: 17 Jan 2019 13:37
URI: http://oceanrep.geomar.de/id/eprint/42900

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