Glacial and deglacial seafloor methane emissions from pockmarks on the northern flank of the Storegga Slide complex |
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| Authors: | T M Hill C K Paull R B Critser |
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| Institution: | (1) Department of Geology and Bodega Marine Laboratory, University of California, Davis, CA 95616, USA;(2) Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039-9644, USA |
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| Abstract: | The Storegga Slide complex is a multi-stage slope failure on the Norwegian continental margin where the most recent major
event occurred 8.1 ka b.p. (calendar years before present). Its northern flank contains pockmark features that are commonly inferred to be related
to the historical and modern venting of methane-bearing fluids. Three jumbo piston cores (JPC), one from a pockmark and two
background cores at variable distances from this site (proximal, 5 km, and distal, 15 km) on the northern flank of the slide
(806–1,524 m water depths), were sampled at 10 cm resolution to assess the geologic record of methane venting in the Nyegga
pockmark field. Six down-core radiocarbon measurements on mixed planktonic foraminifer species reveal ages of 9.4–16.4 ka
b.p. Bathymodiolus mussel shell horizons, indicators of methane-rich environments, have been dated at 15.8–17.6 and ~22 ka b.p. in the pockmark core. Stable isotope analyses on planktonic (Neogloboquadrina pachyderma sinistral) and benthic (Islandiella norcrossi, Melonis barleeanum) Foraminifera reveal δ18O values indicative of a clear glacial/deglacial transition (−1.5‰ shift in planktonic species). Both planktonic and benthic
δ13C signatures record multiple excursions, interpreted to reflect the influence of methane in the environment; these δ13C excursions occur in the pockmark core and also in the distal background core. While authigenic calcite formation on the
seafloor may play an important role in producing such excursions, these data together suggest the influence of methane seepage
within the pockmark field over the past 25 ka, whereby seepage was particularly active between 13 and 15 ka. This is consistent
with previously inferred regional increases in porewater pressure associated with glacial loading and higher sedimentation
rates, which can cause gas hydrate and slope instability. |
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