46345-G2
The Storegga Submarine Landslide: Investigating the Relationship Between Slope Instability, Climate Change, and Gas Hydrates
The Storegga submarine slide, the world's largest known submarine landslide, is part of a recurring history of slope instability documented along the Norwegian margin for the past 1 million years (Bugge et al., 1987; Bryn et al., 2005; Haflidason et al., 2005). While previous studies have accurately dated the slide event (8.1 ka), significant questions remain regarding the causal relationship to gas hydrate stability, and the fate of released methane, a powerful greenhouse gas. This research has focused on investigating microfossil geochemistry to constrain the history of gas hydrates destabilization, slope instability and climate change on the Norwegian margin. 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 (800m water depth), were sampled at 10 cm resolution. Radiocarbon ages indicate variable sedimentation rates of 20 -700 cm/ka at these sites. Concentrated layers of Bathymodiolus mussels, an indicator of methane-rich environments, are dated to 18.2 and 22.2 ka (calendar years before present; 670-710 cmbsf and 780-790 cmbsf, respectively) in one core. Oxygen and carbon stable isotope analysis on planktonic (Neogloboquadrina pachyderma sinistral) and benthic (Melonis barleeanum and Islandiella norcrossi) foraminifera from the piston cores provide a record of temperature change and methane activity in the Storegga Slide area. Oxygen isotopic values show a clear glacial/deglacial transition (-1.48 per mil d18O in planktonics and ~-1.60 per mil d18O in benthics), including Heinrich Event 1 and the Younger Dryas cold interval. Both planktonic and benthic d13C values record multiple excursions interpreted to reflect the influence of methane on the microfossil isotopic composition. While authigenic carbonate may play a role in producing such excursions, this record indicates variable rates of methane seepage from Storegga region pockmarks for the past 25ka. These data indicate that methane seepage activity out of pockmark deposits was variable over the past 25ka, with distinct time periods of increased seepage. Notably, the largest increase in seepage is interpreted to be associated with the most recent deglacial warming episode. These data provide strong evidence for activation of methane seepage via hydrate destabilization during time periods of climatic warming. In contrast, no significant d13C excursions are observed during the timing of the Storegga slide itself. This indicates that methane release from this region likely occurred prior to the massive Storegga event, and that hydrate destabilization was not likely to be associated with the event. In pursuing this research, one Master's student has developed their thesis (R.B. Critser), and two undergraduates were supported for independent research projects and development of laboratory and analytical skills (C. Replogle, C. Whitehouse). Additionally the costs of PI summer salary and analytical supplies were supported by this grant.
