The Heat Is Online

Scientists Worry Seabed Methane Hydrates Will Accelerate Warming

Gas escaping from ocean floor may drive global warming

Ira Liefer, University of California at Santa Barbara

 

(Santa Barbara, Calif.) -- Gas escaping from the ocean floor may provide some answers to understanding historical global warming cycles and provide information on current climate changes, according to a team of scientists at the University of California, Santa Barbara. The findings are reported in the July 20 on-line version of the scientific journal, Global Biogeochemical Cycles.

 

Remarkable and unexpected support for this idea occurred when divers and scientists from UC Santa Barbara observed and videotaped a massive blowout of methane from the ocean floor. It happened in an area of gas and oil seepage coming out of small volcanoes in the ocean floor of the Santa Barbara channel  called

Shane Seep  near an area known as the Coal Oil Point seep field.

 

The blowout sounded like a freight train, according to the divers.

Atmospheric methane is at least 20 times more potent than carbon dioxide and is the most abundant organic compound in the atmosphere, according to the study's authors, all from UC Santa Barbara.

 

"Other people have reported this type of methane blowout, but no one has ever checked the numbers until now," said Ira Leifer, lead author and an associate researcher with UCSB's Marine Science Institute. "Ours is the first set of numbers associated with a seep blowout." Leifer was in a research boat on the surface at the time of the blowouts.

 

Aside from underwater measurements, a nearby meteorological station measured the methane "cloud" that emerged as being approximately 5,000 cubic feet, or equal to the volume of the entire first floor of a two-bedroom house. The research team also had a small plane in place, flown by the California Department of Conservation, shooting video of the event from the air.

 

Leifer explained that when this type of blowout event occurs, virtually all the gas from the seeps escapes into the atmosphere, unlike the emission of small bubbles from the ocean floor, which partially, or mostly, dissolve in the ocean water. Transporting this methane to the atmosphere affects climate, according to the researchers. The methane blowout that the UCSB team witnessed reached the sea surface 60 feet above in just seven seconds. This was clear because the divers injected green food dye into the rising bubble plume.

 

Co-author Bruce Luyendyk, professor of marine geophysics and geological sciences, explained that, to understand the significance of this event (which occurred in 2002), the UCSB research team turned to a numerical, bubble-propagation model. With the model, they estimated methane loss to the ocean during the upward travel of the bubble plume.

 

The results showed that for this shallow seep, loss would have been approximately one percent. Virtually all the methane, 99 percent of it, was transported to the atmosphere from this shallow seep during the blowout. Next, the scientists used the model to estimate methane loss for a similar size blowout at much greater depth, 250 meters. Again, the model results showed that almost all the methane would be transported up to the atmosphere.

 

Over geologic time scales, global climate has cycled between warmer, interglacial periods and cooler, glacial periods. Many aspects of the forces underlying these dramatic changes remain unknown. Looking at past changes is highly relevant to understanding future climate changes, particularly given the large increase in atmospheric greenhouse gas concentrations in the atmosphere due to historically recent human activities such as burning fossil fuels.

 

One hypothesis, called the "Clathrate Gun" hypothesis, developed by James Kennett, professor of geological sciences at UCSB, proposes that past shifts from glacial to interglacial periods were caused by a massive decomposition of the marine methane hydrate deposits.

Methane hydrate is a form of water ice that contains a large amount of methane within its crystal structure, called a clathrate hydrate. According to Kennett's hypothesis, climatic destabilization would cause a sharp increase in atmospheric methane  thereby initiating a feedback cycle of abrupt atmospheric warming. This process may threaten the current climate, according to the researchers. Warmer ocean temperatures from current global climate change is likely to release methane currently trapped in vast hydrate deposits on the continental shelves. However, consumption of methane by microbes in the deep sea prevents methane gas released from hydrates from reaching the ocean surface and affecting the atmosphere.

 

Bubbles provide a highly efficient mechanism for transporting methane and have been observed rising from many different hydrate deposits around the world. If these bubbles escape singly, most or all of their methane would dissolve into the deep-sea and never reach the atmosphere. If instead, they escape in a dense bubble plume, or in catastrophic blowout plumes, such as the one studied by UCSB researchers, then much of the methane could reach the atmosphere. Blowout seepage could explain how methane from hydrates could reach the atmosphere, abruptly triggering global warming.

 

Thus, these first-ever quantitative measurements of a seep blowout and the results from the numerical model demonstrate a mechanism by which methane released from hydrates can reach the atmosphere. Studies of seabed seep features suggest such events are common in the area of the Coal Oil Point seep field and very likely occur elsewhere.

 

The authors explain that these results show that an important piece of the global climate puzzle may be explained by understanding bubble-plume processes during blowout events. The next important step is to measure the frequency and magnitude of these events. The UCSB seep group is working toward this goal through the development of a long-term, seep observatory in active seep areas.

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Natural marine seepage blowout: Contribution to atmospheric methane

GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 20, GB3008, doi:10.1029/2005GB002668, 2006

Ira Leifer

Marine Sciences Institute, University of California, Santa Barbara, Santa Barbara, California, USA

Bruce P. Luyendyk

Earth Science Department, University of California, Santa Barbara, Santa Barbara, California, USA

Jim Boles

Earth Science Department, University of California, Santa Barbara, Santa Barbara, California, USA

Jordan F. Clark

Earth Science Department, University of California, Santa Barbara, Santa Barbara, California, USA

 

Abstract

The release of methane sequestered within deep-sea methane hydrates is postulated as a mechanism for abrupt climate change; however, whether emitted seabed methane reaches the atmosphere is debatable. We observed methane emissions for a blowout from a shallow (22 m) hydrocarbon seep. The emission from the blowout was determined from atmospheric plume measurements. Simulations suggest a 1.1% gas loss to dissolution compared to ~10% loss for a typical low-flux bubble plume. Transfer to the atmosphere primarily was enhanced by the rapid upwelling flows induced by the massive discharge. This mechanism could allow methane suddenly released from deeper (>250 m) waters to contribute significantly to atmospheric methane budgets.  

Received 7 December 2005; accepted 6 March 2006; published 20 July 2006.

Keywords: budget; methane; seep.

Index Terms: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 3307 Atmospheric Processes: Boundary layer processes; 4599 Oceanography: Physical: General or miscellaneous; 4820 Oceanography: Biological and Chemical: Gases.

Citation: Leifer, I., B. P. Luyendyk, J. Boles, and J. F. Clark (2006), Natural marine seepage blowout: Contribution to atmospheric methane, Global Biogeochem. Cycles, 20, GB3008, doi:10.1029/2005GB002668.

(c) Copyright 2006 by the American Geophysical Union.

 

 

Undersea Gas Could Speed Global Warming - Study

Planetark.org, July 21, 2006

 

NEW YORK - If the world continues to get warmer, vast amounts of methane gas trapped in ice under the sea could belch up and worsen climate change, according to a study.

 

"We may have less time than we think to do something (about the prospect of global warming)," Dr. Ira Leifer, a marine scientist at University of California Santa Barbara, said in an interview.

 

Leifer is the main author of a study that looks at how "peak blowouts" of melting undersea formations called methane hydrates could release the potent greenhouse gas into the atmosphere. The study was published Thursday in Global Biogeochemical Cycles, a climate science publication.

 

The distribution of methane hydrates throughout the world is so vast that energy companies hope one day to tap the resource. The US Department of Energy estimates that such formations could harbor as much as 200,000 trillion cubic feet of natural gas.

Hydrate formations exist under hundreds of meters of water in places like the Gulf of Mexico and closer to the surface in permafrost areas of the Arctic.

 

Methane, the main component of the fossil fuel natural gas, has two faces. When burned it releases less carbon dioxide, the main greenhouse gas that scientists believe are warming the earth, than any other fossil fuel.

 

But if it escapes to the atmosphere without being burned, it can trap heat rapidly because it is a greenhouse gas at least 20 times stronger than carbon dioxide.

 

The study measured the amount of methane that escaped to the atmosphere from a peak blowout from small volcanoes on the ocean floor off of California. It found that virtually all of the methane escaping from the deep water reached the atmosphere, countering some theories that methane seeps out in tiny bubbles that harmlessly dissolve in the ocean.

 

Leifer said rising temperatures could warm the oceans, creating a feedback loop in which warm temperatures make global warming even worse.

 

Most scientists believe emissions of heat-trapping gases from cars, industrial sources and the burning of forests are warming the earth. NASA has said that 2005 was the warmest year at the earth's surface since records began in the 1860s.

 

While deep ocean temperatures have been more stable, currents of gradually rising sea-surface temperatures could eventually warm the ocean's depths and release gas, said Leifer. "If you expose a hydrate to water that's warmer than normal it starts destabilizing," he said.

 

"I have no doubt that if we warm the atmosphere too much the oceans will follow and will cause the problem to become severe at some point."