Underwater methane emission in the Arctic | Polarjournal
The oceanographic vessel namedHelmer Hanssen belongs to the University of Tromsø, which uses it for climate studies and bottom trawling. Image: Erlend Bjørtvedt / Wikimedia

While we are struggling to reduce our greenhouse gas emissions, Norwegian scientists have just discovered a new natural source of methane that diffuses from the Arctic Ocean’s subsoil.

The gas beads up from between the underwater rocks, returns to the surface and reaches the atmosphere. A new source of greenhouse gases, and more precisely of methane, has just been discovered in the Arctic, under the surface of the ocean. This was published in the journal Nature two weeks ago by Pavel Serov and his Norwegian colleagues from the Arctic University of Norway and the Norwegian Petroleum Agency. They inventoried more than 7,000 leaks between the North Cape and the Svalbard archipelago.

These leaks are natural, but still little known, they would date from the end of the last ice age, about 15 thousand years ago, and would have formed when glaciers retreated, leaving apparent openings.

During an expedition with the oceanographic vessel Helmer Hanssen, acoustic instruments detected gas eruptions from the bottom. The gas escapes in the form of columns of bubbles which are grouped in clusters of 3 km2 on average and some of them degas without neighbors at less than 500 m. However, the latter remain rare and represent only 3% of the observed leaks.

Other expeditions, such as the one led by the University of Geneva and the Pacific Association on board the sailing ship Mauritius, are looking for clues about these methane sources. The gas is dissolved in the surface of seawater, and when its concentration exceeds the equilibrium between the atmosphere and the ocean, the methane passes from the surface into the air. Image: Pacific / Twitter

East of Bear Island, the Sentralbanken high has the highest gas density with over 100 seeps per km2. Two areas are also very active, Storbankenhigh, further north and one near Kong Karl in Svalbard.
In these areas, water samples are saturated with methane from the bottom to the surface. The geological formations that caused the leaks have been eroded and openings 2 to 5 kilometers wide are leaking hydrocarbon fumes. Under its openings, the reservoirs are sometimes fed through faults by other deeper reservoirs dating from the Paleozoic.

Covering these leaks, sedimentary layers 3 to 10 meters thick bear traces of friction of ancient glaciers, the action of retreats and extension of glacial tongues may have swept the sediment and reduced this layer. In addition, these leaks are located on the edge of the continental shelf in areas of geological uplift that have also reduced the thickness of sediments usually covering the hydrocarbon reserves.

Comparable areas were found near the United States with 570 seeps. Similar conditions make Greenland and the Canadian archipelagos favorable places to pursue this research. The authors believe that there are many more of these sources, however the Barents Sea is surely the area of the sea floor with the most leakage from the Arctic.

Camille Lin, PolarJournal

Link to study: Serov, P., Mattingsdal, R., Winsborrow, M., Patton, H., Andreassen, K., 2023. Widespread natural methane and oil leakage from sub-marine Arctic reservoirs. Nat Commun 14, 1782. https://doi.org/10.1038/s41467-023-37514-9

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