Balancing atmospheric methane budgets is difficult, yet it is necessary to understand them, and how they vary over time, if their influence on global climate change is to be evaluated. The community of geoscientists, bioscientists and oceanographers working on seabed fluid flow (natural gas seeps, mud volcanoes, gas hydrates, etc.) is aware that methane emissions from the seabed are widespread in the world’s seas and oceans. However, this paper is perhaps the first to pull together sufficient evidence to demonstrate that gas hydrates are not alone in contributing seabed methane to the marine and atmospheric environments—and in influencing global climate change.

Rather than making a "new discovery" the paper brings together existing knowledge and ideas to develop a new argument for the importance of marine geology and the oceans, which hitherto have been regarded as insignificant in terms of their impact on the global climate.

Methane is one of the most important "greenhouse gases," so understanding methane budgets is essential if we are to understand the impact of human emissions. Although the overall methane budget is known, the contribution of natural seabed sources seems to have been overlooked. The only seabed methane source generally recognized is gas hydrate—an ice-like material, widespread in deepwater sediments, in which vast quantities of methane are stored. However, in this paper other seabed methane sources, such as mud volcanoes and gas seeps, are identified. It is argued that changes in sea level, as well as the extent of ice and permafrost, control the emissions from these sources, and that they act as a "'geological thermostat" moderating climatic extremes.

My involvement in seabed fluid flow started with my doctoral research in the late 1970s. At first I studied seabed features (pockmarks) formed by escaping fluids (gas), but soon realized that the fluid was more important than the features. My research subsequently expanded to include an interest in all the consequences of seabed fluid flow, and the fate of escaping methane, including influences on marine biology and the composition of the atmosphere.

Dr. Alan Judd
School of Marine Science & Technology
University of Newcastle
Newcastle upon Tyne, U.K.