Acoustic estimates of methane gas flux from the seabed in a 6000 km2 region in the Northern Gulf of Mexico

Seeps of free methane gas escaping the seabed can be found throughout the ocean basins. To understand the role of methane gas seeps in the global carbon cycle-including both gas added to the atmosphere and that which is dissolved and potentially oxidized in the ocean volume-it is important to quantify the amount of methane escaping the seabed. Few large-scale mapping projects of natural methane seeps have been undertaken, however, and even among these, quantitative estimates of flux are rare. Here we use acoustic mapping techniques to survey 357 natural methane seeps in a large region (6000 km(2)) of the northern Gulf of Mexico and outline a general approach for methane seep mapping using a combination of multibeam and split-beam echo sounders. Using additional measurements collected with a remotely operated vehicle (ROV) together with the acoustic mapping results, we estimate the total gas flux within the 6000 km(2) region to be between 0.0013 and 0.16 Tg/yr, or between 0.003 and 0.3% of the current estimates for global seabed methane seepage rates.