From the sea floor off the U.S. West coast escapes for a long time the mass of methane. Researchers Paul Johnson of the University of Washington in Seattle have now studied how this comes about: In a study in the “Journal of Geophysical Research: Solid Earth,” report of 491 sources on the bottom of the sea in front of the U.S. state of Washington and the canadian city of Vancouver. Their spatial distribution could provide information about the Tsunami risk in this earthquake-prone Region.
The methane escapes the bubbles in the area of the so-called Cascadia-subduction zone, one of the tectonically most sensitive regions of the earth. At a distance of a few centuries severe earthquakes occur there, some with a Magnitude of nine. The last is more than 300 years. A new quake would threaten cities such as Seattle and Vancouver; therefore, it is important to understand how the sea floor is to obtain the methane could contribute to bubbles.
bubble it is mainly in the rather shallow water
According to the survey of researchers, the majority of methane sources are arranged in such a depth of 160 metres in a narrow North-South Band along the U.S. West coast. The so-called Juan de Fuca plate pushes under the North American plate. Here, sediments are scraped off and between the plates squeezed together. By the compression of methane is released, which escapes in bubbles from the sea floor.
there is a strong earthquake in the Region, pushed the plates on top of each other, the researchers suggest. In fractures through which the methane after the other, can escape arise – that is, the hypothesis is shortened by Johnson’s Team. For she speaks, that the bubbles of the greenhouse gas occur mainly in rather shallow water. Thus, they occur more frequently in places where the soil under the sea has a the process of matching layering of loose Sediment under the more dense Rock.
This observation could help to understand the earthquakes in the Region. If such a quake, the sea floor actually moves, especially in the shallow water near the coast, it would be for a smaller Tsunami than the quake occurs in greater depth. The US-geologists propose that the other available, but in your view, less likely explanations for the spatial distribution of methane sources. Was excluded, which had placed earlier studies suggest: that increasingly warm sea water dissolves frozen methane out of the ground.
fishing boats give information about outlet
Although there is evidence to suggest that global warming is elsewhere, so-called methane hydrates to melt, but the methane that was trapped under high pressure in the ice. A large part of it is decomposed on the way to the surface of micro-organisms into CO2.
In the studied case, were able to show the scientists, however, that the methane bubbles are based on processes that act over a longer period of time than the man-climate change. “Also, estimates from our previous Work on Methane emissions from both the American and canadian West coast have shown that there are no anthropogenic effects to hide behind the observations”, says Michael Riedel from the Geomar Helmholtz centre for ocean research in Kiel.
Typically, researchers looking for sources of Methane with a special measuring procedure, with which, for example, the bottom of the sea can map. There is however also an amazingly simple, although admittedly less accurate method: You just have to keep fishing boats on the look-out. Some of these methane-eating micro-organisms to other living beings as food, which are, in turn, of other animals of prey. Second-to-last link in the food chain of fish, which are eventually caught by people. This has a visible impact, as the main author Johnson explains: it is possible To identify on satellite data, that the flows of methane as a rule, the rights of a tangle of fishing boats.
(editing Tamedia)
Created: 09.04.2019, 15:17 PM