Ocean warming and gas hydrate stability on the mid-Norwegian margin at the Storegga Slide

Abstract

The sensitivity of oceanic gas hydrates and submarine slope stability to the combined forcing of sea level changes and bottom water perturbation is a critical issue for risk assessment in the Storegga Slide area on the mid-Norwegian margin. Evidence for the existence of gas hydrates both inside and outside the Storegga Slide complex comes from reflection seismic profiles, where a bottom-simulating reflection marks today's base of the gas hydrate stability zone. Paleo-bottom water temperatures show a relatively fast increase at approximately 12.5–10 ka (calendar years) following the Younger Dryas while stable warm water conditions have prevailed since then. Despite sea level rise, this warm-water inflow caused a major reduction in the thickness of the gas hydrate stability zone along the upper slope of the mid-Norwegian margin. Modelling results indicate that critical hydrate stability conditions and consequently the maximal potential pore pressure build-up occur at the location of the Storegga Slide headwall. Although the major phase of hydrate melting predates the Storegga slide event, dated at 8.2 ka (calendar years), reduced hydrate stability conditions could have facilitated or contributed to sub-marine slope failure. Additionally, the bottom-simulating reflections within the slide complex seem to have nearly adjusted to new equilibrium conditions, highlighting the dynamics of hydrate stability in continental margin sediments under environmental changes (climate change, geohazards).