Distribution of free gas in marine sediments: a global overview

To quantify the global distribution of free gas in shallow marine sediments , we have identified and indexed over 100 documented cases in the scientifi c and engineering literature. Our survey confirms previous assumptions, pri marily that gas bubbles are ubiquitous in the organic-rich muds of coastal waters and shallow adjacent seas. Acoustic turbidity, as recorded during se ismo-acoustic surveys, is the most frequently cited evidence used to infer the presence of seafloor gas. Biogenic methane predominates within these sh allow subbottom deposits. Because of their global prevalence, growing inter est in gassy marine sediments is understandable, as their presence can have profound scientific, engineering and environmental significance.