Methane Hotspots Where the Siberian Arctic Sea 'Boils' Studied by Scientists

Last year Russian scientists announced they had come across an area in the East Siberian Sea that was "boiling" with methane. Team leader Igor Semiletov said it was the "most powerful gas fountain" he had ever seen, and that "no one has ever recorded anything like this before."

Over recent decades, scientists have debated how much these methane "hotspots" contribute to climate change. Methane is a powerful greenhouse gas with a higher ability to trap heat than carbon dioxide. While most emissions come from manmade activities, such as agriculture and leaks from natural gas systems, it is also produced naturally through geological sources and the breakdown of organic material. The methane coming from the Arctic seafloor belongs to the latter.

How much is produced is unclear, however, so creating accurate models for future Arctic emissions is difficult. Some researchers believe huge amounts are being released and this will have a major impact on the climate, while others were less sure.

In a study published in Science Advances, a team of researchers led by Brett Thornton, from Stockholm University, went on a two-month expedition to the Arctic to take measurements of methane coming from the East Siberian Arctic Shelf, off the Russian and Alaskan coasts.

"This is a large, shallow shelf sea. Methane might be released from geologic sources, or from long-buried and/or frozen, now thawing and degrading, organic material in the sediment," Thornton told Newsweek. "Because the sea is so shallow, and underlain by permafrost that was above sea level during the last ice age, it contains large amounts of organic materials. Plus, these seas receive huge amounts of organic materials from the large rivers draining Siberia.

"The problem is, if this huge amount of methane is coming out of the sea, then we are missing a major part of the global methane emissions, and our understanding of global methane is wrong," Thornton said. "But many land stations making measurements of methane around the Arctic Ocean haven't seen large increases of methane that would be expected from large sea emissions. So what is actually happening? The way to answer this is to go to sea and make direct measurements."

The researchers took measurements from the sea at various depths. They used a system that allowed them to measure how much methane was coming out of the ocean, taking into account the gas concentration, the wind around the ship and the movement of the ship. In doing this, they were able to work out how much methane was actually reaching the atmosphere. When methane is released on the seafloor, much of it is destroyed by the ocean on its way up. The main way for it to reach the atmosphere is through bubbles.

"The ocean is very hostile to methane," Thornton explained. "Microbes use it for food, for one thing. Methane that dissolves into the deep sea has little chance of ever reaching the atmosphere. Bubbles make it more likely, but even with bubbles, methane rapidly exchanges with other gases dissolved in the ocean, such that even if the bubbles reach the sea surface, they have often lost most of their methane.

"Methane hotspots—really plumes of bubbles from the seafloor—are important because bubbles have a chance of rapidly moving methane from the seafloor to the atmosphere, before the ocean has time to destroy it."

The team found that overall, methane bubbles contribute very little of the greenhouse gas to the atmosphere. The total amount of methane emitted each year is estimated to be about 560 teragrams (one teragram is equivalent to around 1.1 million U.S. tons.) They estimated that the entire East Siberian Arctic Shelf contributes around 3.02 Tg/year. In deeper water, methane emissions were lower. At hotspots, where methane bubbles at the surface in concentrated areas, it was far higher. But these hotspots were found to be very small and a rarity, Thornton said.

"If [methane emissions] were much larger—if the widely-reported hotspots were more common—then it is important globally. Learning that these hotspots seem relatively rare is good news for [the] climate," he said.

The researchers now plan to return to other areas of the Arctic Ocean to take more measurements: "The Arctic Ocean is fairly understudied, and the shrinking ice cover means more opportunities for greenhouse gas releases and sometimes even uptake from the atmosphere," Thornton said. "We need to understand the Arctic system today, so we can predict what is going to happen in the future."