An invisible force appears to be boiling up the waters of the Baltic Sea near the Danish island of Bornholm. White, circular areas, from above it looks like looking into a pot of boiling pasta water. The impression is created by the gas masses bubbling to the surface through leaks in the Nord Stream 1 and 2 pipelines from around 50 meters below sea level. A few hundred million cubic meters of natural gas could be released in the coming days if the residual gas is not somehow pumped out of the pipelines. In addition to the geopolitical consequences, it is unclear what this means for animals, plants and the entire Baltic Sea ecosystem.
The current images are reminiscent of an environmental catastrophe in the Gulf of Mexico almost twelve years ago, the consequences of which continue to this day. After a series of technical failures, the Deepwater Horizon drilling platform caught fire and sank. As a result, around 700 million liters of oil flowed into the sea for 87 days.
Unlike the oil spill in 2010, however, experts estimate the acute consequences for the Baltic Sea as locally limited – at least assuming that no more gas is permanently pumped into the destroyed pipelines. Natural gas consists mainly of non-toxic but flammable methane (CH₄). The exact composition depends on the respective deposit from which the gas was extracted. It is not yet clear which mixture was in the destroyed pipelines.
The explosion is believed to have primarily harmed marine mammals at first
The geologist Jens Schneider von Deimling from the Institute for Geosciences at the University of Kiel expects a local fish kill. “At this time of year, the deep water in the Bornholm Basin is usually very low in oxygen. The gas flow allows the anoxic water to reach the surface locally.” The fish in the region would then suffocate. The probably violent detonation probably mainly harmed marine mammals in the waters, suspects the geologist, who explored gas wells in the North and Baltic Seas in addition to acoustic methods by submarine and has even touched a pipeline – without causing any damage. But if gas doesn’t flow in for weeks because it’s being pumped up on the Russian side, the damage will probably remain small-scale. “Otherwise the situation would have to be reassessed.”
It is also unclear how much of the gas dissolves in the Baltic Sea water and how much escapes directly into the atmosphere. At the beginning, when the pressure in the pipes was still at its highest, most of the gas was probably blown directly into the air. As the pressure decreases, the proportion that dissolves in the water increases. Experts estimate that 50 to 70 percent could remain in the water at low pressure. The dissolved gas can feed microbes, which are likely to multiply as a result.
To what extent this in turn will affect the ecosystem cannot yet be foreseen, says Ellen Damm, biogeochemist at the Alfred Wegener Institute. That also depends on the direction in which the dissolved gas cloud, or “plume” in technical jargon, drifts in the water. To the east, the sea is “like a bathtub”, where high concentrations of methane could possibly accumulate. Consequences for the ecosystem? Not clear. If the cloud drifts west, the thinning in the Atlantic helps to minimize further effects on the environment. “If gas constantly flows out of the pipelines with little pressure, biotic communities could form there that consume methane,” says Damm.
Initially, 500 tons of the greenhouse gas methane flowed out of the leak every hour
In any case, the damage to the climate from the leaks is likely to be significant. It is true that methane only remains in the atmosphere for around twelve years on average before it is broken down. During this time, however, the gas warms the atmosphere much more than the same amount of carbon dioxide. Atmospheric researchers therefore give different values for the climate damage of methane depending on the time horizon: viewed over 100 years, one tonne of methane is around 28 times more harmful to the climate than one tonne of CO₂, and over 20 years even 84 times more harmful.
But how much has escaped into the atmosphere? It is known that Nord Stream 2 was filled with around 300 million cubic meters of gas. There was only a pressure drop on one of the two legs of the pipeline, the other appears to be intact. In the case of Nord Stream 1, on the other hand, both tubes are damaged – but it is unclear how much gas they contained before the detonations. The operating company and the Russian authorities are keeping a low profile on this.
If just one tube were to lose its entire contents, 200,000 tonnes of methane would be emitted, says Paul Balcombe, a chemical engineer at Imperial College London. That would be more than double the 2015 Aliso Canyon leak, one of the largest documented methane leaks to date. At peak times, around 50 tons of methane per hour escaped from the gas storage facility near Los Angeles. According to a “conservative estimate”, the rupture of the three Nord Stream tubes initially released more than 500 tons of methane per hour, as a spokesman for the satellite company GHGSat said.
If one optimistically assumes that a total of 200,000 tons of methane escaped, which would enter the atmosphere directly and not be dissolved in the water, this would equate to a release of 5.6 million tons of CO₂, based on a time horizon of 100 years . This is a significant burden on the atmosphere, according to Dave Reay, a climate researcher at the University of Edinburgh. At the same time, it is “a drop in an ocean compared to the vast amounts of so-called ‘fugitive methane’ that are released around the world every day from things like fracking, coal mining and oil exploration.” The International Energy Agency estimates, based on satellite measurements, that the energy sector releases 135 million tons of methane every year in this way, around 370,000 tons a day.
With material from the Science Media Center