Dynamics of methane migration in marine hydrate systems: Examples from the Guaymas Transform, Blake Ridge, and Storegga landslide

Methane hydrates are a common feature on the world's continental margins. The ice-like, crystalline solid of methane and water has been proposed to represent as much as 50% of the world's organic carbon. With such a vast quantity of hydrocarbons present in these regions, it is important to understand the movement of methane in these systems, and the factors affecting methane migration and therefore distribution on a smaller scale. Three study areas (Gulf of California, Blake Ridge, and Storegga Slide) were chosen to provide a cross-section of the different environments in which hydrates occur, in order to gain a more complete picture of the controls on the methane migration process. The Gulf of California is an active margin where migration of methane is controlled by heat and fluid flow generated from the young oceanic crust in the region. Advective heat flow modeling at the vent site indicates a maximum upward fluid velocity 0.032 m/yr, which is significantly above the background fluid velocity of 0.001 m/yr. Similarly, the highest advective fluid flow rates corresponded to the highest thermal gradients 584°C/km above the 125°C/km background.; The methane migration in the Blake Ridge of the US Atlantic margin is controlled by the erosion and deposition of the sediments by contour currents. In the sediment wave field the erosion has allowed methane to escape from a large region. This methane escape now controls the diffusive flux in the wave field. Elsewhere on the ridge, deposition of sediments has created overpressures resulting in a massive movement of methane from the free gas zone into the hydrate stability zone. Velocity modeling for hydrate and free gas concentration found that of the 915,615 moles of methane missing from the free gas zone, 59.5% of which can be accounted for in a zone of slightly coarser grained sediment known as the hydrate stringer.; In the Storegga Slide, the presence of gas hydrates is controlled by the presence of a leaky hydrocarbon system, not the slide itself. Velocity modeling for hydrate and free gas concentrations show little change in the average methane concentration inside versus outside the slide.