Emplacement mechanisms of submarine landslides and their effect on ocean circulation and climate

Abstract

Submarine landslides are some of the largest-scale geological events on the surface of the planet. They can generate dangerous tsunamis posing serious geohazards. They move large (up to 3,000 km3) amounts of material and can disintegrate to form large clouds of sediment. The main aim of this thesis is to use global circulation models to study the effect of these sediment clouds on the ocean circulation and climate. A driver for this question is the coincidence in time of the largest submarine landslide in the geological record, the Storegga Slide, and the last major extreme climatic event, the 8.2 ka cold event.
Arctic regional ocean circulation models are set up to simulate a large and dense water mass at the bottom of the Norwegian Basin. A mechanism for the dense mud cloud to influence the circulation is shown. The main driver for the perturbation is the strong steric effect generated, i.e. changes in density generating changes in surface height; this increases incoming fluxes of water into the Nordic Seas, increasing the freshwater content. Subsequently we observe a reduction in convection in the Nordic Seas and ex- ported deep water through Denmark Strait, thus affecting the Meridional Overturning Circulation (MOC).
This climate influencing mechanism proves to be robust under a number of different parameter choices ranging from the size and concentration of the perturbation to the horizontal resolution of the model to the timescale of the perturbation. It is therefore suggested that the Storegga Slide might have played a major role in the 8.2ka cold event.
Finally, a case study from the Norwegian Margin is presented, using a newly collected high resolution multibeam bathymetry dataset together with a recompilation of sites on the Norwegian coasts to study landslide frequency and tsunamigenesis. It is shown that multiple large (>400 km3) landslides can occur during a single glacial period over the same area, contrasting with previously suggested theories that only one slide can occur during each glacial period. Moreover, it is concluded that not all large submarine landslides generate large and widespread tsunamis.

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