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USGS Report of Methane Hydrate Off Southern California Sparks Media Interest
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
(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 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.
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in this issue:
Submarine Groundwater Discharge Study USGS Assists in Search for Airplane Wreckage
Falmouth Science Teachers visit USGS Woods Hole Sea-Floor-Mapping Systems Described on New Web Pages
Multiple Award Winner in USGS Photography Contest
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U. S. Department of the Interior | U.S. Geological Survey
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