INGERSON LECTURE: METHANE HYDRATES CHARACTERIZATION AND ROLE IN PAST AND FUTURE CLIMATE CHANGE

Gas Hydrate is a naturally occurring clathrate whose solid H₂O lattice hosts small guest gaseous molecules in cages under moderate to high pressures and low temperatures. The stability also depends on the type of guest gas molecules(s) and pore fluid geochemistry. In the modern oceans the pressure, temperature, and methane concentration constraints restrict them to the uppermost few hundred meters of sediments on submerged continental margins where water depths exceed ~500m. In the oceans the amount of gas hydrates is enormous, ~10¹⁹ g of methane C stored in them. On Earth methane is the dominant gas in the hydrates.

Recent interest in natural gas hydrates has resulted from recognition that global warming may destabilize some of the vast quantities of methane hydrate in shallow marine slope sediments (and permafrost). The potential environmental consequences of rapid release of large quantities of methane for both ocean and atmosphere are important questions surrounding the huge amounts of gas hydrates in the shallow geosphere. When methane is released into the ocean, some is bacterially oxidized, thus the amount potentially released into the atmosphere is reduced. Locally extensive oxygen will be consumed and CO₂ produced by this aerobic methane oxidation, hence, the capacity of the ocean to incorporate fossil fuel CO₂ will be somewhat reduced. Environmental stresses or geologic perturbations, such as global warming, rapid deglaciation, earthquakes, or tectonic uplift, may trigger giant landslides in margins that could rapidly and catastrophically release large quantities of methane to the ocean and atmosphere with complex climatic feedbacks. New evidence exists that in the geological past, massive methane releases from gas hydrate occurred and was possibly associated with global warming, for example in the late Paleocene, ~55.6 Ma.

Methane gas is an important contributor to the atmospheric radiation balance as it is a significantly more effective greenhouse gas than CO₂.