Do methane hydrates, pockets of gas trapped in permafrost ice and on the ocean floor, risk releasing their gas into the atmosphere? To find out, 80 scientists will take turns, until 1er October, aboard the French oceanographic vessel Why not ? in the Black Sea, one of the most important gas hydrate melting theaters in the world. “Hydrates were formed there when the Black Sea was still just a freshwater lake, before the opening of the Bosphorus Strait with the Mediterranean nine thousand years ago. The massive influx of seawater then slowly changed its temperature and salinity at depth ”, traces Vincent Riboulot, geology researcher at Ifremer and head of the Ghass 2 mission (Gas Hydrates, fluid Activities and Sediment deformations in the western black Sea). “It is this combination of factors, reinforced by the current climate change, which today precipitates the melting of hydrates in this place. ” Helped by around thirty sailors and a dozen French universities, Ifremer researchers will locate and measure this melting. “We will carry out flow and concentration measurements over the entire water column, from the bottom to the surface, to see if there is a methane anomaly in the atmosphere”, details Vincent Riboulot. If the methane released is not observed in the air, it is because it dissolves in water and thus contributes to the acidification of the oceans.
Seismic reflection – an imaging technology similar to ultrasound – will be used to describe the properties of subsurface and marine sediments. “With these images, we have a section of the seabed, usable by geologists. The release of methane hydrates in water can be observed as soon as the temperature, pressure and salinity conditions are no longer met ”, describes Stéphan Ker, geophysicist and co-responsible for the mission. Ghass 2 should ultimately lead to a more precise assessment of the climatic and geological risks of hydrate melting. Thanks to a first mission in 2015, Ifremer researchers had already shown, in a study published in Nature Communications, the importance of salinity in the destabilization of hydrates. They had estimated between 40 to 200 billion cubic meters the amount of gas that could be released over five thousand years.