"We don't know of any explanation that fits as well as methane," said lead study author Adam Skarke, a geologist at Mississippi State University in Mississippi State.

Surprising seeps

Between North Carolina's Cape Hatteras and Massachusetts' Georges Bank, 570 methane seeps cluster in about eight regions, according to sonar and video gathered by the National Oceanographic and Atmospheric Administration ship Okeanos Explorer between 2011 and 2013. The vast majority of the seeps dot the continental slope break, where the seafloor topography swoops down toward the Atlantic Ocean basin. [Gallery: Amazing images of Atlantic Methane Seeps]