AmericanChemicalSociety.com

The proposed research aimed to understand the role of methane seepage in promoting slope instability associated with the Storegga Submarine Slide. 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, Melonis barleeanum) foraminifera provide both chronostratigraphic records and proxies for methane venting. Oxygen isotopic values show a clear glacial/deglacial transition (-1.5 per mil shift in planktonic and -1.3 per mil shift in benthic foraminifera). Both planktonic and benthic d13C values record multiple excursions, interpreted to reflect the influence of methane in the benthic sedimentary environment. This record indicates occurrences of methane seepage within the pockmarks over the past 25 ka B.P, concentrated during the termination of glaciation and warming in to the modern Holocene period. These findings are consistent with the inferred regional changes in porewater pressure associated with glacial loading and changing sedimentation rates. Surprisingly, this research did not find a strong connection between methane seepage and the Storegga Slide itself, only evidence for pulses of methane release in this region during the past 25,000 years. This project supported the research of one M.S. student (Critser) and promoted the development of a strong collaborations between the PI and new colleagues. Results from this project were included in one publication by the PI and two other coauthored publications.