1. Department of Geological Sciences, Stockholm University, 10691 Stockholm, Sweden.
2. Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA.
3. Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT The Arctic University of Norway, 9037 Tromsø, Norway.
4. Geological Survey of Norway, 7491 Trondheim, Norway.