Greenhouse Gases Bubbling up from Inside the Earth

When Eskimos in Canada light gases, which have accumulated underneath the ice, and have a barbecue on the flame or when the ocean bed resembles an orange peel and features pockmarks of up to several hundred metres in diameter, the same phenomenon makes an appearance: In those regions, methane from the earth’s interior escapes to the surface. Some lakes in Canada bubble so intensively then, they seem to be boiling. Yet so far nobody knows what amounts of methane escaped from such sources yesterday, last month or some million years ago. Geoscientists like Professor Dr. Rolando di Primio and Dr. Torsten Sachs from the GFZ therefore ask themselves, how much methane escapes into the air from these and other sources in the earth’s interior. For each methane molecule heats up the climate some 25 times more than a carbon dioxide particle.

By contrast, the enormous amount of carbon from which the gas may originate is better known: “The earth’s sedimentary basins contain 10 to the power of 16 tons of carbon from organic sources”, Rolando di Primio reports. To further illustrate this amount, the geochemist adds a comparison: “This is ten thousand times more carbon than all the coal, oil, natural gas and all organisms on earth combined.” This carbon deposit has formed over the course of hundreds of millions of years from dead organisms remaining on the ground or at the bottom of water bodies and which have been covered by other sediments over time. Chemical, physical and biological processes continuously change this gigantic mass and in doing so also create the fossil raw materials mined by modern civilisation as peat, coal, oil or natural gas and burns in power stations and motors. In the process, the greenhouse gas carbon dioxide is released.

However, the fact that by various processes the carbon deposits in the sediments create greenhouse gases such as carbon dioxide and methane also in the earth’s interior which then can escape to the surface through cracks and fissures has so far not drawn much attention. When examining theunderground with sound waves, they obtain crosscut sections of the ground. Yet from some areas underneath the surface the method does not render any information, one only sees vertical zones with “white noise”. “These are so-called gas chimneys, that is, areas in which methane flows through the sediments in a bundle”, explains di Primio. The orange peel ocean bed and the gas escaping from the ground the Eskimos ignite for their barbecues are nothing but leaks in the earth from which this methane escapes.

In Canada’s west, geoscientists find so-called tar sands, which originated some 65 to 55 million years ago. The oil contained therein was in part decomposed by bacteria already back then and this process continues to this day, producing large quantities of methane. During the same time, the average temperatures on earth rose to levels significantly exceeding those of today. Since methane is a greenhouse gas, a connection is conceivable. “Yet there are altogether some 500 such sedimentary basins on earth”, knows di Primio. Hardly any of these have been examined so far as regards contemporary and previous leaks for greenhouse gases. In any case, in western Canada methane from sediments escapes into the air to this day. In order to understand how much these gases from within the earth influence the climate, the researchers thus intend to examine the sedimentary basins in more detail. “Yet it is difficult to derive from single measurements how much methane may escape into the air from a larger area”, explains GFZ researcher Torsten Sachs, who, amongst other things, has researched the methane emissions from the permafrost soils of Siberia.

This problem can be solved by way of a device developedby GFZ researchers in cooperation with colleagues from the Institute of Environmental Physics at the University Bremen. This “Methane Airborne Mapper” or short “MaMap” measures diffused sunlight from the infrared spectrum from out of an aeroplane or helicopter. From a height of a thousand metres, this well over 120 kilogramme heavy spectrometer can determine the methane concentration across areas each 35 metre long and 25 metre wide and thus quickly obtains a relatively detailed image of greenhouse gas emissions also of larger regions. A first test aboard the Polar 5 research aeroplane from the Alfred Wegener Institute went very well. Further flight missions should give Torsten Sachs valuable indicators as regards the amounts of methane escaping from the earth world-wide. And possibly the Eskimos in Canada can soon find new locations for their barbecue evenings with the help of the MAMap data.