THE GLOBAL PRODUCTION OF METHANE FROM SHALLOW SUBMARINE SOURCES

Since methane, per mole, has a global warming potential 3.7 times that of carbon dioxide (LASHOF and AHUJA, 1990, Nature, 344, 529-531) it is one of the most important greenhouse gases in the atmosphere. It is therefore crucial to acquire a basic understanding of the natural global methane emission variability and inventory. Methane contained in and seeping from shallow marine sediments represents a vast, but largely uncharted source of ocean and atmospheric methane. A rough global estimate is made here on the amount of methane annually venting through the seabed from shallow marine sediments in water depths less than 250 m. The globally extrapolated estimate is based on observations of methane point sources in the North Sea. These estimates show that marine sediments probably represent an important but variable source of methane to the atmosphere. However, much more survey work and detailed measurements are needed before a more exact figure on total source strength and variability can be provided.