Marine deposits of methane hydrate are estimated to be large and are thought to be important to climate change and seafloor stability, as well as representing a potentially exploitable energy resource. The extent of these deposits can usually be inferred from seismic imaging. In this study, using high-resolution seismic sections of seafloor sediments in the Cascadia margin off the coast of Vancouver Island, Canada, lateral variations in the base of hydrate stability zone (upper 220 m of sediment) are observed, including gas-rich vertical intrusions into the hydrate stability zone. The presence of gas within the hydrate stability zone suggests that the zone might have been perturbed by warm fluids, occasionally resulting in a seafloor pockmark. These perturbations significantly increase the surface area and subsequently the volatility of the methane hydrate reservoir. Increased area implies that significanty more methane hydrate lies close to being unstable and hence closer to dissociation in the event of a lowering of pressure due to sea-level fall. The high-resolution images of the methane hydrate stability zone and its lower boundary depicted here support a model of hydrate distribution strongly affected, if not dominated, by focused vertical fluid flux. This complicates the estimation of methane hydrate quantities obtained through extrapolation from a single drill hole, and indicates that of the estimated 10000 Gt of carbon sequestered in methane hydrates, a significantly greater portion might lie closer to the stability boundary than if it were evenly distributed throughout an unperturbed stability zone.
Decreased stability of methane hydrates in marine sediments owing to phase-boundary roughness
Die Verringerung der Stabilität von Methanhydraten in marinen Sedimenten durch die Phasengrenzen-Rauhigkeit
Nature ; 420 , 6916 ; 656-660
2002
5 Seiten, 4 Bilder, 21 Quellen
Aufsatz (Zeitschrift)
Englisch
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