Refining the distribution and evolution of methane seeps along the U.S. Atlantic margin

From U.S. Geological Survey Coastal and Marine Hazards and Resources Program and Mississippi State University Major new research Hundreds of previously unknown submarine methane seeps in the United States Atlantic Margin (USAM) were documented, and the sedimentary, geological, and oceanographic processes that led to the formation of the seeps were described. The published research lays the foundation for the ocean community to conduct interdisciplinary research on the evolution of USAM seeps, seep biogeochemical processes, and benthic seep communities over the next decade.

Gases and liquids often leak from the seafloor into the ocean, transferring carbon and other materials into the seawater. When new seafloor is formed at mid-ocean ridges, heat Hydrothermal Carbon dioxide emissions from features such as black smokers can contain sulfides, dissolved metals, hydrogen and methane. In other cases, underwater volcanoes spew large amounts of carbon dioxide into the ocean. The new study focuses on another more common fluid flow feature:Cold SeepCold seeps typically release methane and form far from plate boundaries or faults in environments ranging from shallow river deltas to thousands of meters below the seafloor.

The recently published study used water column images acquired during multibeam sonar surveys aboard six research vessels between 2011 and 2016 to locate streams of bubbles leaking into the ocean from seafloor gas seeps. previous studies Published in 2014 Some scientists also described the surprising discovery of more than 550 methane seeps between Cape Hatteras, North Carolina, and Georges Bank, offshore Cape Cod. The new study adds about 1,400 new identifications of gas plumes to this part of the U.S. Atlantic margin. After removing duplicate plumes that may have been detected multiple times in different ocean cruises, about 1,100 unique seeps remained. When the seep locations were analyzed using a spatial clustering algorithm, there appeared to be about 275 seep fields from offshore South Carolina to Georges Bank, including 47 clusters containing between five and 138 individual seeps. The largest seep cluster was located in the main channel of the Hudson Canyon and in an unnamed canyon 18 kilometers south of the Norfolk Canyon, which has been dubbed the Norfolk Seep.

The new study combines Update the leak database Earthquake data collected by the United States Geological Survey 2015 2018 MATRIX SurveyThe seismic data provided high-resolution images of the features of the seafloor beneath the seep. These images revealed faults, eroded sediments, gas chimneys and submarine landslide deposits that provided clues to the formation of the seep.

Most of the seeps described in the study are located in the uppermost continental slope, where water depths are less than about 500 meters (1,640 feet). Methane hydrateGas hydrates — a solid, ice-like substance of water and methane that is stable at low temperatures and high pressures — are present in the sediments. This means that the methane emissions cannot originate from the decomposition of methane hydrates directly beneath these seeps. However, the paper suggests that gas hydrate dynamics could explain the formation of seeps on upper slope headlands overlooking major shelf break canyons such as the Norfolk, Washington, Baltimore and Wilmington canyons.

The new study also revealed rare seeps at depths of about 1,000 to 1,400 meters (3,300 – 4,600 feet) off the coast of Virginia and Massachusetts. The methane gas from these seeps is likely being released through the breakdown of gas hydrates in the underlying sediments.