Gas Hydrates in Marine Sediments: Lessons from Scientific Ocean Drilling

Certain low-molecular-weight gases, such as methane, ethane, and carbon dioxide, can combine with water to form ice-like substances at high pressure or low temperature.These compounds, commonly called gas hydrates, concentrate gas in solid form and occur naturally in sediment beneath the Arctic permafrost and in the sediments of the continental slope.A decomposing piece of gas hydrate can be ignited and will sustain a fl ame as the methane is released, producing the phenomenon of "burning ice."Ocean drilling has proven to be an important tool for the study of marine gas hydrate systems, which have been increasingly recognized as important to society.In some places, methane hydrate may be concentrated enough to be an economically viable fossil fuel resource.However, geohazards may be associated with gas hydrates as well, through largescale slope destabilization (e.g., Maslin et al., 2004) and release of methane, a potent greenhouse gas.Indeed, evidence collected from deep-sea sediments suggests that major global warming episodes in the past were associated with massive methane releases from gas hydrate deposits (e.g., Dickens et al., 1995;Hesslebo et al., 2000), although this hypothesis remains controversial (e.g., Bowen et al., 2006).Climate changes over the late Quaternary have also been linked to re-