A massive methane leak has been discovered in the deepest reaches of the Baltic Sea, causing a bubble of greenhouse gases to rise much higher in the water column than scientists expected.
In August, researchers discovered a huge leak 1,300 feet (400 meters) below the surface during an expedition to Landsault Deep, the deepest point in the Baltic Sea. The methane leak covers an area of approximately 7.7 square miles (20 square kilometers), the size of about 4,000 football fields.
“It’s basically bubbling everywhere in these 20 square kilometers.” Marcelo Ketzer“We’re trying to find a solution to this problem,” the project leader and professor of environmental science at Linnaeus University in Sweden told Live Science.
On shallow coastal seabeds, methane bubbles up from decaying organic matter, but at deeper water methane tends to spread out by diffusion, meaning bubbles are not needed. Most of the diffused methane remains in the deepest water. However, the new leak does not follow this pattern.
“By discovering this, [leak]We realized that there is a completely different mechanism that supplies methane to the Baltic Sea floor,” Ketzer said.
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The research team was also stunned to observe how far the methane bubbles rose through the water column toward the ocean surface. Methane is normally soluble in water, so as the bubbles rise, they decrease in size until they disappear.
Ketzer said the maximum height the methane bubbles were expected to reach was about 165 feet (50 meters) above the ocean floor. But at Landsort Deep, the team observed methane bubbles reaching 1,250 feet (380 m) deep in the water column, or just 65 feet (20 m) below the surface.
“So it’s something completely new,” Ketzer said.
He believes this is at least partly due to a weaker-than-average microbial filter – a layer of bacteria that lives in the sediment and “eats” up to 90% of the methane produced by decaying material. ing. Ketzer said the filters can be several feet thick in the ocean, but only a few centimeters thick in the Baltic Sea.
Kretzer said human activity is also changing the way this filter works.
Fertilizers that reach the ocean from land promote algae growth. When the algae die, organic matter is added to the sediment. Methane-eating bacteria also love to eat this material, allowing more methane to escape toward the surface. Additionally, the researchers believe that Landsort seafloor leakage may be caused by large amounts of sediment deposited there by undercurrents.
“We don’t know to what extent we are responsible for weakening this filter and allowing more methane to pass through, but we’re looking into it,” Ketzer said.
Additionally, the water at the bottom of the Baltic Sea contains high levels of methane, so bubbles may have to travel higher in the water column to dissolve, which explains how bubbles It does not completely explain how close to the surface the surface is.
Ketzer’s team is preparing a second expedition to Landsort Deep to see if the bubbles reach the surface and release methane into the atmosphere.
Such methane leaks are a potentially important source of greenhouse gases that scientists need to account for. Ketzer estimates that there may be six other deep-sea methane fields in the Baltic Sea.
“We continue to discover new locations where seepage is occurring.” anna michellean associate scientist at Woods Hole Oceanographic Institution, who was not involved in the project, told Live Science via email. “It will be interesting to see if exploration of other parts of the Baltic Sea uncovers more methane leaching sites.”