AmericanChemicalSociety.com

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.. The northern flank of the Storegga Slide complex contains pockmark features that are commonly inferred to be related to the venting of methane-bearing fluids.. Three jumbo piston cores (JPC), two taken from separate pockmarks and one core taken near the pockmarks on the northern flank of the Storegga Slide (806 to 1524 m water depths), were sampled at 10 cm resolution to assess the history of methane venting in this area. Ten radiocarbon measurements indicate sediment ages from 11 to 25 Ka B.P. Bathymodiolus mussel shell horizons, indicators of methane-rich environments, are dated to 18.2 and 24.5 Ka B.P. (calendar years before present) in one core. Oxygen and carbon stable isotope analysis on planktonic (Neogloboquadrina pachyderma sinistral) and benthic (Islandiella norcrossi) foraminifera provide both chronostratigraphic records and proxies for methane venting, respectively. Oxygen isotopic values show a clear glacial/deglacial transition (-1.5‰ shift in planktonics and -1.3‰ shift in benthics). Both planktonic and benthic d¹³C values record multiple excursions, interpreted to reflect the influence of methane in the benthic sedimentary environment. While authigenic calcite formation on the seafloor may play a role in producing such excursions, this record indicates occurrences of methane seepage within the pockmarks over the past 25 Ka B.P. These data indicate that methane seepage is concentrated over Termination 1A, which is consistent with the inferred regional changes in porewater pressure associated with glacial loading and sedimentation rates.