A new study led by the researchers has discovered more than 500 bubbling methane vents on the seafloor off the US east coast. The scientists have observed streams of bubbles and believe there is an abundance of circumstantial evidence pointing to methane.

The seeps were discovered in a stretch of ocean waters from Cape Hatteras, North Carolina to Massachusetts. In a paper published online Sunday in the journal Nature Geoscience, the scientists, including Adam Skarke of Mississippi State University and Carolyn Ruppel of the United States Geological Survey, reported evidence that the seepage had been going on for at least 1,000 years.

Dr. Carolyn Ruppel, chief of the U.S. Geological Survey's Gas Hydrates Project in Woods Hole Massachusetts, mentions that most of the seeps had been found in depths of about 800 to 2,000 feet, where the methane, which is produced by microbes, is most likely trapped in sediments near the seafloor, within cage like molecules of ice called hydrates. Natural variability in water temperatures, caused by ocean circulation and other factors, may be warming these hydrates just enough to release the gas.

Methane is a potent greenhouse gas, and gas hydrates are thought to hold up to 10 times as much carbon as the earth's atmosphere. The researchers conclude that the depths of the seeps suggest that in most cases the gas did not reach the atmosphere but rather dissolved in the ocean, where it could affect the acidity of the water by reducing oxygen levels.

Dr. Ruppel reveals that there could be about 30,000 of these hidden methane vents worldwide and could be adding as much as 90 tones of the planet-warming gas to the atmosphere or overlying waters each year.

Sampling the bubbles along with the waters in and around the plumes will help scientists estimate the effects of the methane emissions.