Environmental Science and Engineering Seminar
Gas hydrate, a naturally occurring, ice-like solid consisting of methane and water, forms at the pressures and temperatures (P-T) common in the sediments of marine continental margins and in areas of continuous permafrost. The global distribution of gas hydrate deposits, the large volumes of methane they sequester, and the fact that shallow hydrates are poised close to the P-T limits for their stability render hydrates susceptible to breakdown (dissociation) under changing climate conditions. Indeed, some researchers predict catastrophic dissociation of hydrates and the release of their methane into the ocean-atmosphere system if climate continues to warm in the 21st century. Current IPCC atmospheric methane budgets attribute ~1% of annual emissions to gas hydrate dissociation despite the lack of evidence that hydrate-derived methane is reaching the atmosphere. Based on geochronologic data, methane possibly sourced in dissociating gas hydrates may have been leaking from the seafloor on upper continental slopes for the past few millennia. Under present-day ocean conditions, methane emitted from the seafloor in gas hydrate areas appears to be consumed by water column bacteria before the methane crosses the sea-air interface. At high latitudes, methane hydrate in continuous permafrost areas should remain stable for centuries more. The relatively small volumes of gas hydrate that persist in association with subsea permafrost on Arctic Ocean margins following warming since the Last Glacial Maximum could dissociate over that same period.