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USGS Report of Methane Hydrate Off Southern California Sparks Media Interest


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discovery core shows white methane hydrate mixed with dark mud
Above: This discovery core shows white methane hydrate mixed with dark mud. The core penetrated and recovered a sample of the upper 2.1 m (5 ft) of a mud volcano 24 km (15 mi) off the southern California coast in the Santa Monica Basin; for details, see the February 2006 issue of Geology (v. 34, no. 2, p. 109-112). Photograph by James Conrad, USGS. [larger version]

the Monterey Bay Aquarium Research Institute revisited the mud volcano in the Santa Monica Basin with their remotely operated vehicle Tiburon
Above: In February 2005, the Monterey Bay Aquarium Research Institute (MBARI) revisited the mud volcano in the Santa Monica Basin with their remotely operated vehicle (ROV) Tiburon. The ROV used a clear plastic funnel attached to a push-core tube to collect bubbles of methane gas emerging from the seafloor at around 800-m depth. (Venting methane gas bubbles can be seen streaming upward behind the manipulator arm.) As the gas collected within the push core, it combined with cold (5°C) seawater to form the ice-like hydrate visible in this image. © 2005 MBARI [larger version]

A U.S. Geological Survey (USGS) cruise conducted off southern California in July 2003 unexpectedly recovered methane hydrate from the summit of a mud volcano, in a piston core taken at 800-m water depth (see "USGS Scientists Discover Gas Hydrate in Southern California During Cruise to Study Offshore Landslides, Earthquake Hazards, and Pollution" in Sound Waves, November 2003). USGS researchers studying that core, and other samples collected during the cruise, recently published their findings in the February 2006 issue of Geology (v. 34, no. 2, p. 109-112). The publication set off a flurry of media coverage, mostly focused on the discovery of the methane hydrate, an icelike crystalline solid in which methane gas molecules are trapped. Methane hydrate, which occurs in the pores of permafrost and sub-sea-floor sediment in many places around the globe, is of interest as

  • a potential energy source (various nations are trying to determine how to mine it economically),
  • a possible trigger of undersea landsliding (methane gas released during dissociation of the hydrate, caused by changes in the temperature or pressure conditions that allow it to form, has the potential to destabilize surrounding sediment),
  • a possible contributor to abrupt global climate change (widespread dissociation of methane hydrate—triggered, for example, by rising sea level and consequent changes in sub-sea-floor pressure—could release large amounts of methane gas, a key contributor to the atmospheric warming known as the greenhouse effect), and
  • an unknown variable in the global carbon mass balance (we do not know how much carbon is stored in methane hydrate worldwide, nor how much carbon is trapped in pockets of gas beneath impermeable methane hydrate "caps").

(Visit URL http://woodshole.er.usgs.gov/project-pages/hydrates/ for additional information about methane hydrate and URL http://walrus.wr.usgs.gov/cabrillo/tierra/methane
_hydrate.html
for additional information about the 2003 discovery off southern California.)

The mud volcano where the methane hydrate was discovered is in the Santa Monica Basin, just 24 km (15 mi) offshore from Los Angeles, the second largest urban region in the United States. Approximately 300 m in diameter at its base and 30 m high, the feature is formed by mud, gas, and fluids moving upward from the sediment fill and perhaps from deeper sources as well, probably along fault ruptures. Other mud volcanoes in the region may likewise host methane hydrates. The proximity of the recently discovered methane hydrate to shipping lanes from Los Angeles and Long Beach would make this deposit particularly difficult to mine.

The mud volcano was discovered in 1992 by USGS scientist Bill Normark and his colleague from the Geological Survey of Canada (GSC), David J.W. Piper, who spotted it in seismic-reflection data collected during a cruise aboard the GSC research vessel Parizeau to study turbidite sedimentation in the Santa Monica Basin. The mud volcano also appears on the seaward edge of multibeam-sonar data collected by USGS scientists Jim Gardner and Peter Dartnell in 1998. When Normark and USGS scientist Jim Hein conferred to pick sampling sites for the 2003 cruise, the mud volcano was an obvious choice for collecting samples that Hein planned to analyze for chemical evidence of fluids and trace metals moving up to the sea floor along faults.

The gas and associated fluids venting through the sea floor at the mud volcano site are at approximately the same temperature as the surrounding seawater (approx 5°C) and so are termed a "cold seep." Like other cold seeps, the Santa Monica Basin site supports dense populations of bivalves. The site is unique, however, in that the composition of the bivalve shells indicates an unusually large amount of methane gas moving upward through the sediment. The shells are severely depleted in the carbon isotope 13C—in fact, they are the most 13C depleted shells of marine macrofauna yet reported. The scientists interpret this extreme 13C depletion as evidence for the extreme flux of methane. Methane sources include breakdown of organic matter in the basin sediment and possible contributions from older hydrocarbon source rocks. Abundant heavy metals (such as mercury, cadmium, thallium, and silver) indicate leaching of basement rocks by fluid circulating along an underlying fault, which also allows for a high flux of fossil methane.

The paper reporting these findings, entitled "Methanogenic calcite, 13C-depleted bivalve shells, and gas hydrate from a mud volcano offshore southern California," was authored by five USGS scientists—Jim Hein, Bill Normark, Brandie McIntyre, Tom Lorenson, and Chuck Powell—and published by the Geological Society of America (GSA) in its journal Geology. GSA routinely asks authors to write a short paragraph about their paper, which is then incorporated into a press release sent to more than 300 science writers worldwide. The paragraph written by first author Hein caught the attention of Alicia Chang of the Associated Press (AP), who called Hein for an interview and then wrote an article based on the interview, the press release, and the Geology paper. Chang's article was picked up by hundreds of newspapers worldwide, including newspapers from every State in the United States, both major and local. The story appeared on many news Web sites (for example, see URL http://abcnews.go.com/Technology/wireStory?id=1552545) and aired on CBS affiliate radio stations around the country after CBS News, N.Y., conducted a phone interview with Hein. Importantly, the USGS' Web site was cited in most of the stories. Ann Cairns (GSA media relations) said that the media response to this paper was among the largest they have seen for papers published by GSA.

Closeup of the mud volcano in a high-resolution seismic-reflection profile
Above: Closeup of the mud volcano in a high-resolution seismic-reflection profile created from Huntec deep-tow boomer data collected by the Geological Survey of Canada in 1992. The boomer source and receiver were towed about 200 m below the sea surface; resolution is about 40 cm. V.E., vertical exaggeration. [larger version]

Seismic-reflection profile collected by the Geological Survey of Canada in 1992.
Above: Seismic-reflection profile collected by the Geological Survey of Canada in 1992. The mud volcano from which methane hydrate was recovered in 2003 is labeled "Hydrate Site." Note that internal reflectors are not visible in or below the mud volcano; they are obscured by gas contained in the sediment and by deformation of the sediment as it was squeezed up to form the mud volcano. South of the mud volcano are additional areas where deeper reflections are not visible, probably because of gas accumulating along horizons as shallow as 60 m below the sea floor. The width of the black line above the mud volcano represents the 30-m-diameter circle within which core samples were collected in 2003. [larger version]


Related Sound Waves Stories
USGS Scientists Discover Gas Hydrate in Southern California During Cruise to Study Offshore Landslides, Earthquake Hazards, and Pollution
November 2003
Gas Hydrate in the Northern Gulf of Mexico Has Puzzling Characteristics and Could Pose a Hazard to Deep Drilling
July 2003
Gas Hydrate Studied in the Northern Gulf of Mexico
September 2002

Related Web Sites
Gas Hydrate Studies
U.S. Geological Survey (USGS)
Methane Hydrate
U.S. Geological Survey (USGS)
Scientists Find Frozen Methane Gas Deposit
ABC News

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in this issue: Fieldwork
cover story:
Monitoring Eruption of Augustine Volcano

Submarine Groundwater Discharge Study

USGS Assists in Search for Airplane Wreckage

Research Methane Hydrate off Southern California Coast

Outreach Open House at FISC St. Petersburg

Falmouth Science Teachers visit USGS Woods Hole

Sea-Floor-Mapping Systems Described on New Web Pages

Awards Wetland Ecologist Named Fulbright Senior Specialist

Multiple Award Winner in USGS Photography Contest

Staff USGS Scientist on Nanjing University Committee

Publications March 2006 Publications List


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