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Karin Andreassen and her colleagues were funded through the Research Council of Norway with grant money earmarked for understanding methane release from the seafloor. It's well-known that methane bubbles up from the sediments under the ocean in the Arctic, Andreassen told Live Science, but these small seeps don't reach much higher than 650 feet (200 meters) into the water column above the ocean bottom. The gas dissolves back into the ocean water before it can reach the atmosphere.
Explosive methane eruptions might be much different. Andreassen and her team took the research vessel Helmer Hanssen to the Barents Sea off the northern coast of Norway. The researchers used a variety of techniques, such as collecting seafloor sediment samples. They also beamed acoustic and seismic signals to the ocean floor and subsurface and used the echoes to map the contours below.
The researchers discovered more than 100 giant craters, each up to 0.6 miles (1 kilometer) wide and nearly 100 feet (30 meters) deep, in an area of 170 square miles (440 square km). The scientists also discovered many previously undiscovered mounds, known as pingos. These pingos are lumps of methane hydrate, or methane gas frozen within a lattice of water molecules.
Importantly, Andreassen said similar blowouts could happen in the near future on account of climate change. Areas in front of retreating ice sheets in Greenland and West Antarctica could host underlying hydrocarbon reservoirs. These blowouts don’t happen very often, but their environmental impacts could be greater than the impacts of slow and gradual methane seepage, explained Andreassen. That said, it’s not clear if the abrupt and massive methane releases of the past reached the upper atmosphere.
“We have not documented that it could, yet,” she told Gizmodo.
More work is clearly needed to understand the nature and power of these historical blowouts, and to assess their environmental impacts. The finding also points to the need to further study the potential reserves of hydrocarbons beneath the ice sheets of West Antarctica and Greenland.
It’s important to point out that natural methane leaks aren’t exclusive to the Arctic. Last year, scientists mapped one of the longest active methane seeps on the planet—a strip extending from British Columbia to Northern California. Recent surveys have also documented hundreds of methane seeps along the Atlantic continental margin, and it’s assumed that thousands more could exist around the globe. Scientists are only starting to get a grip on how much methane is escaping from the bowels of the planet, and how it might be influencing our climate.