THE BOTTOM OF THE ATLANTIC OCEAN Forty miles off the coast of North Carolina, the 274-foot research vessel Atlantis paced a dark, empty swath of ocean in evenly spaced lines as the crew pinged sound waves into the deep. A quarter-mile below, plumes of methane, a potent greenhouse gas, rose from the seafloor.

The underwater site, named Pea Island after an area of the Outer Banks, is one of the hundreds of active methane seeps discovered off the Atlantic coast since 2012. No human had ever explored this particular underwater world. Samantha Joye, an oceanographer and microbiologist, was about to change that.

She strolled into the ships computer lab at 6 a.m., a thermos of tea in hand. She looked anxious as she checked in on what the sonar had turned up.

Jason Chaytor, a marine geologist with the U.S. Geological Survey, had spent half the night mapping the ocean floor. He pointed to the columns of bubbles visible in the rainbow-colored images. The largest of the plumes extended some 250 meters from the bottom, about halfway to the surface.

Youre going to visit this first, Chaytor told her.

Joye leaned over his shoulder and squinted through purple-framed glasses. A mad scientist grin washed over her face.

The site is whats known as a cold seep, an area where methane and other hydrocarbons naturally eject from the seafloor. Cold seeps are home to diverse communities of organisms, including Joyes favorite: beggiatoa, a large, thread-like bacteria.

Along with their ability to capture energy from poisonous hydrogen sulfide gas, beggiatoa form colonies, or mats, that are hot spots for hitchhiking microorganisms that feast on methane. Working together, these communities of microbes act as biological filters, blanketing active seeps and limiting the amount of gas that enters the water column and, more importantly, the atmosphere.