Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study rules out ancient 'bursts' of methane from seafloor deposits

28.08.2006
A dramatic increase about 12,000 years ago in levels of atmospheric methane, a potent greenhouse gas, was most likely caused by higher emissions from tropical wetlands or from plant production, rather than a release from seafloor methane deposits, a new study concludes.

This research, to be published Friday in the journal Science, contradicts some suggestions that the sudden release of massive amounts of methane frozen in seafloor deposits may have been responsible – or at least added to - some past periods of rapid global warming, including one at the end of the last ice age.

The findings were made with analysis of carbon isotopes from methane frozen in Greenland ice core samples, by researchers from Oregon State University, the University of Victoria, University of Colorado, and the Scripps Institution of Oceanography at the University of California-San Diego.

For climate researchers, an understanding of methane behavior is of some significance because it is the second most important "greenhouse gas" after carbon dioxide. Its atmospheric concentration has increased about 250 percent in the last 250 years, and it continues to rise about 1 percent a year.

"Methane is a gas that makes a significant contribution to global warming but has gone largely unnoticed by the public and some policy makers," said Hinrich Schaefer, a postdoctoral research associate in the OSU Department of Geosciences. "Its concentration has more than doubled since the Industrial Revolution, from things like natural gas exploration, landfills, and agriculture. We need to know whether rapid increases of methane in the past have triggered global warming or just been a reaction to it."

To better answer this question, researchers studied two stable isotopes of carbon found in methane, that can provide a better idea of where the methane came from during a period thousands of years ago when Earth was emerging from its most recent ice age, and entering the interglacial period that it is still in. At that time, methane concentration went up 50 percent in less than 200 years.

Several things naturally produce methane, including biomass burning, geologic sources, wetlands, animals, and aerobic production by plants, a mechanism that was unknown until just recently. And huge amounts of methane – with more carbon stored in them than all the known oil and gas fields on Earth – are found in methane hydrates on the seafloor. In this setting, the cold temperatures and pressure keep the methane stable and prevent it from entering the atmosphere.

But some researchers have theorized that something might release the trapped seafloor methane – submarine landslides, a drop in pressure caused by dropping sea levels, or warming of ocean waters.

If that happened, it might cause a huge increase in atmospheric levels of methane and global warming. Some have hypothesized that this may be one of the factors that help cause cyclical ice ages – as ice levels rise and sea levels drop, methane might be released from the seafloor hydrates, causing global warming and an end to the ice age. Then the process would start over again.

"There have been estimates that releasing even 1 percent of the methane hydrates in the seafloor could double the atmospheric concentration of methane," said Ed Brook, an associate professor of geosciences at OSU and co-author on the study. "So we looked to the past to see if that may have happened during previous periods of rapid global warming."

Based on their isotopic analysis of the methane from the Greenland ice cores, the researchers concluded that it did not come from seafloor hydrate deposits or "gas bursts" of methane associated with them. The most likely candidates, they said, were higher emissions from tropical wetlands or larger amounts of plants, or some other combination of sources.

If the rise in methane had come from seafloor hydrate deposits, the study found, the atmospheric levels of methane would have had a different isotopic "signature" than they actually did.

There are still important questions to answer about methane in Earth's atmosphere and the role it may play in global warming, the scientists said. For one thing, the current understanding of methane sources and sinks does not completely explain the isotopic signature of methane now found in the atmosphere. This indicates that estimates of methane emissions, including the human-made contribution, may have to be revised.

There are also concerns, they said, about methane trapped in permafrost across wide areas of the Earth's Arctic regions. There are significant amounts of methane found in this permafrost that could be released if it melted, and also organic material associated with melting permafrost that could cause further increases in methane. This might cause "a fairly significant rise in the total level of atmospheric methane of around 20 percent," Schaefer said.

By largely ruling out major bursts of methane from seafloor deposits during a period of global warming, however, this study suggests there may not be any "reinforcing" greenhouse mechanism from that cause. The increase in tropical wetlands or other factors that caused a large, rapid methane increase at the end of the last ice age may be relevant to future changes in methane, but changes in land use and vegetation cover due to human activities complicate the analysis of this issue, the scientists said.

Researchers at OSU are international leaders in the study of past climate changes, some of which have been surprisingly rapid - on the order of years or decades - and the mechanisms that cause them. These studies were funded by the National Science Foundation, American Chemical Society, and other grants and fellowships.

Ed Brook | EurekAlert!
Further information:
http://www.geo.oregonstate.edu

More articles from Earth Sciences:

nachricht Climate satellite: Tracking methane with robust laser technology
22.06.2017 | Fraunhofer-Gesellschaft

nachricht How reliable are shells as climate archives?
21.06.2017 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Study shines light on brain cells that coordinate movement

26.06.2017 | Life Sciences

Smooth propagation of spin waves using gold

26.06.2017 | Physics and Astronomy

Switchable DNA mini-machines store information

26.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>