Ocean warming and its consequences for gas hydrate and continental margin slope stability: The Norwegian Margin

Juergen Mienert, Ph.D.

University of Tromsø, Norway

Scripps Institute of Oceanography


Wednesday, March 19, 2003

Pacific Forum — 3:00 p.m.



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The sensitivity of ocean gas hydrates and submarine slope stability to sea level changes and warm water perturbation is a critical issue for continental margin development in general, and for the Norwegian Margin in particular. Relatively rapid warm water inflows after the Last Glacial Maximum (LGM) occurred during the Younger Dryas (YD) at approx. 11.5 cal ka BP and stable warm water inflow conditions in the period after 9.8 to 8 cal ka BP. This inflow caused major reductions in the thickness of the Gas Hydrate Stability Zone (GHSZ) as shown by modeling results, first in the deeper and then in shallow water continental slope sediments. Such a pattern of gas hydrate melting implies that the continental slope was first vulnerable to slope failure in the deeper water and afterwards in the shallower sites of the margin.

Here, we argue that the major phase of hydrate melting that occurred in depth shallower than 500 m coincides with the Storegga slide event at 8.2 cal ka BP. This conclusion is based on observations and modeling using existing bottom water temperature and sub-seabed temperature profiles. The slide events have impacted major parts of the total GH area, which were vulnerable to slope failure after the YD in an area of approx. 12,000 km2. A geological explanation model for the giant Storegga slide (Bryn et al. 2003) shows that a new ice age with a rapid deposition of glacial sediments is needed to create a large-scale unstable situation.