Methane sources: Climate change is innocent

Gas leaks off Spitsbergen were caused by post-glacial uplift

The MARUM-MeBo70 drill comes back on board after successful sampling on the seabed off Spitsbergen. © MARUM / University of Bremen / G. Bohrmann
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Acquittal for climate change: The release of methane on the seabed off Spitsbergen is certainly not due to man-made global warming. Analysis of drill samples shows that methane has been bubbling out of the sediment for thousands of years. This is probably due to the melting of ice sheets after the last ice age. Because the associated pressure relief made unstable methane compounds in the soil - and the greenhouse gas was released.

Methane is known to be a potent greenhouse gas: its greenhouse effect is up to 30 times higher than that of carbon dioxide. Gas is a natural component of our environment, is the main constituent of natural gas, and is present in many regions of the ocean in the form of methane hydrates, also known as burning ice.

However, these compounds of water and methane are stable only under high pressure and cold temperatures. If the pressure is too low or the temperature too high, the hydrates dissolve: The methane is released as gas and escapes from the seabed. Researchers have been observing such methane sources for years, for example, in the Mediterranean Sea, the Black Sea and the Arctic Ocean off Spitsbergen.

White methane hydrate layers traverse the sediments. © MARUM / University of Bremen / G. Bohrmann

What is the reason?

But what is the reason for these outgassing? Is global warming due to climate change, or is it due to other, natural processes behind it? To clarify this question, Klaus Wallmann from the Helmholtz Center for Ocean Research in Kiel and his colleagues have taken a closer look at the sea area around Spitsbergen.

For the first time, they were able to use a special drilling rig to extract particularly long sediment cores in the region and thus look back into the past. "In it, we found significant amounts of S wasser that originate from dissolved hydrates, " reports Wallmann colleague Gerhard Bohrmann from the University of Bremen. display

Landnahme as probable explanation

The special feature: this fresh water is already 8, 000 years old. The process of hydrate dissolution must therefore have started even then, so it can not be caused by the climate warming of the past decades. But what would trigger the process then? A possible explanation for this provided the researchers with a model simulation of ice distribution in the Arctic since the last ice age.

The results showed: "After the melting of the ice sheets, the land has risen faster and stronger than the sea level rose, " says Borhmann. "This relieved the pressure on the hydrates and eventually they became unstable." According to the researchers, post-glacial uplift is the most likely cause of methane release off Spitsbergen - and not climate change. Whether this also applies to other areas of the Arctic or in middle latitudes, will now show further research. (Nature Communications, 2018; doi: 10.1038 / s41467-017-02550-9)

(GEOMAR Helmholtz Center for Ocean Research Kiel, 09.01.2018 - DAL)