The findings, to be published Friday in the journal Science, are good news for those who have worried that this unusual mechanism of releasing methane into the atmosphere might provide a serious reinforcement to global warming at some point in the future.
The five-year project was funded by the National Science Foundation, American Chemical Society and other agencies.
It now appears almost certain that the major methane increases that occurred near the end of the last Ice Age were due to the growth of wetlands and the methane releases associated with that, which occurred shortly after some significant warming in the Northern Hemisphere. They did not come from sudden bursts of methane trapped in deep seafloor deposits.
The newest conclusions were made possible by identification of some ancient ice exposed at the edge of a Greenland ice sheet, and samples of it cut with chain saws that totaled thousands of pounds.
"To get enough air trapped in ice to do the types of measurements we needed, it took some of the largest ice samples ever worked on," said Edward Brook, a professor of geosciences at Oregon State University, and international expert on using ice samples to explore ancient climate.
"The test results were unequivocal, but it was a lot of heavy lifting," Brook said. "It was like working in a quarry. We could have used some help from the OSU football team."
Methane, and the possible sources of it, is a significant concern to scientists because it is a potent greenhouse gas. It has natural sources in places like wetlands and permafrost, and its concentration has more than doubled since the Industrial Revolution from human activities such as natural gas exploration, landfills and agriculture. Natural gas used for home heating is composed mostly of methane.
But more hidden, and potentially of much greater concern, are massive deposits of methane buried beneath the sea in solid hydrate deposits, where cold temperatures and pressure supposedly keep it stable and unable to enter the atmosphere in large amounts. There have been concerns that this methane might be released suddenly by warming of ocean waters or other causes. These huge deposits of methane hold more carbon in them than all the known oil and gas fields on Earth.
If only 10 percent of that seafloor methane were to be released in a few years, it could be the equivalent of a 10-fold increase in the level of atmospheric carbon dioxide, the researchers said in their report. And 12,000 years ago, methane levels went up 50 percent in less than 200 years, according to studies by Brook and others. Researchers wanted to know why.
"There are hundreds to thousands of times more methane trapped in seafloor deposits than there is in the atmosphere, and it's important that we know whether it's stable and is going to stay there or not," Brook said. "That's a pretty serious issue."
To test whether the seafloor deposits had been the source of the large methane increase thousands of years ago researchers measured levels of carbon 14, an isotope of carbon, from the Greenland ice samples. The seafloor deposits are old and have very little carbon 14 in them. Based on the results of those measurements, the scientists were able to determine whether the methane increases 12,000 years ago were linked to seafloor deposits or not.
"The data made it pretty clear that seafloor methane hydrates had little to do with the increase in methane thousands of years ago," Brook said. "This largely rules out these deposits either as a cause of the warming then or a feedback mechanism to it, and it indicates the deposits were stable at that point in time. The increased methane must have come from larger or more productive wetlands that occurred when the climate warmed."
Researchers now hope to do similar experiments in Antarctica to verify the results of this study, Brook said.
This research was a collaboration of scientists from Oregon State University, the Scripps Institution of Oceanography, Australian Nuclear Science and Technology Organisation, National Institute of Water and Atmospheric Research in New Zealand, National Space Institute in Denmark, and the Commonwealth Scientific and Industrial Research Organisation in Australia.
Edward Brook | EurekAlert!
Early organic carbon got deep burial in mantle
25.04.2017 | Rice University
New atlas provides highest-resolution imagery of the Polar Regions seafloor
25.04.2017 | British Antarctic Survey
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
25.04.2017 | Earth Sciences
25.04.2017 | Life Sciences
25.04.2017 | Earth Sciences