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Gas Hydrate Studied in the Northern Gulf of Mexico By Bill Winters and Tom Lorenson September 2002 in this issue: next story The 120-m-long French research vessel Marion Dufresne recently recovered a 64.5-m-long giant "Calypso" piston core. A giant piston-coring cruise with multiple objectives was recently completed by a group of scientists from the United States, France, Germany, the Netherlands, Canada, Japan, Greece, Russia, and Mexico to better understand natural-gas-hydrate distribution across the continental slope of the northern Gulf of Mexico. Gas hydrate, an icelike crystalline solid containing high concentrations of methane, is a potential energy resource. It is also a hazard to hydrocarbon exploration and production, and may influence global climate change. Although the amount of gas hydrate in the natural environment is enormous, little is known about its distribution in sea-floor sediment or even exactly how it forms. Exploring these and other questions was among the goals of the recently completed coring cruise conducted jointly by the Institut Polaire Fran�ais, Paul-ƒmile Victor (IPEV), and the U.S. Geological Survey (USGS) aboard the 120-m-long French research vessel Marion Dufresne. The cruise, partly funded by the U.S. Department of Energy, originated in Cancœn, Mexico, on July 1 and ended in Tampa, FL, on July 18. Coring from the Marion Dufresne was conducted within three areas of the northern Gulf of Mexico—Tunica Mound, Bush Hill, and Mississippi Canyon—to investigate the effect of different geologic settings and sub-sea-floor conditions on the presence of gas hydrate. Additional coring was conducted in Pigmy and Orca Basins to study pollutant sequestration and contaminant-input history. Unlike any U.S. research vessel, the Marion Dufresne has a unique, unobstructed starboard main deck that allows the deployment and recovery of IPEV's "Calypso" corer. That piston-coring system, driven by a 6-tonne weight stand, has obtained cores as long as 64.5 m. In the Gulf of Mexico, 18 giant Calypso piston cores as much as 38 m long were collected under the direction of the chief of operations, Yvon Balut (IPEV), at Tunica Mound, at Bush Hill, and near or within the Mississippi Canyon (see map). The cores are being used to study the distribution of natural gas hydrate through geochemical analyses of pore water and gas samples, as well as physical-property measurements obtained from the cores. The results are also being correlated with seismic records to assess the potential for using such records to locate sub-sea-floor gas hydrate. The Gulf of Mexico is unique in the world for containing significant amounts of both biogenic gas hydrate (hydrate formed in shallow sediment by microbial production of methane) and thermogenic hydrate (hydrate formed by deep natural gas leaking into the shallow subsurface sediment). The possible presence of gas hydrate in the northern Gulf of Mexico has been inferred from geophysical data, but before this cruise, samples have been recovered from only the uppermost few meters of sediment by shallow coring or submersible vessels, typically on sea-floor mounds. Much of this cruise focused on finding evidence for the existence of gas hydrate away from obvious sea-floor gas-hydrate mounds and at depth in the sediment. The generation of gas caused by hydrate dissociation was spectacularly demonstrated when the uppermost several meters of one core blew vertically out the end of the core barrel, flew at least 10 m into the air, and landed in the gulf waters next to the ship. The gas hydrate remained on the surface of the water because of its low density and floated away as it dissociated. Other gas hydrate, recovered during the cruise, was present either as particles distributed throughout the sediment or as massive chunks that filled the entire 10-cm diameter of the core liner. The hydrate samples were preserved in liquid nitrogen for future shore-based laboratory testing. Above: (Clockwise from bottom left) Rendy Keaten (MBARI), Charlie Paull (MBARI), Bill Waite (USGS), Jim Flocks (USGS), Tom Lorenson (USGS), and Patrick Mitts (MBARI) marking and cutting 1.5-m-long sections from one of 18 giant piston cores. Below: Chunks of gas hydrate recovered from a giant piston core. [larger version] Shipboard participants included Tom Lorenson (cochief), Pat Hart, and Jennifer Dougherty (USGS, Menlo Park, CA); Bill Winters (cochief) and Bill Waite (USGS, Woods Hole, MA); Jim Flocks (USGS, St. Petersburg, FL); Charlie Paull, Bill Ussler, Steve Hallam, Rendy Keaten, and Patrick Mitts (Monterey Bay Aquarium Research Institute [MBARI]); Ivana Novosel (University of Victoria, BC, Canada); John Pohlman (College of William and Mary); Olya Boldina (Moscow State University); Yifeng Chen (University of Tokyo); and Efthymios Tripsanas (Texas A&M University). Considerable at-sea help was provided by an international group of about 40 scientists under the IMAGES (International Marine Past Global Changes Study) and PAGE (Paleoceanography of the Atlantic and Geochemistry) programs (Laurent Labeyrie and Viviane Bout, cochiefs). The IMAGES program is an international effort to understand the mechanisms and consequences of climatic changes by using the oceanic sedimentary record. Also deeply appreciated was onshore assistance from Dave Mason (USGS, Woods Hole, MA), Jesse Hunt (Minerals Management Service, New Orleans, LA), Bill Gwilliam (Department of Energy, Morgantown, WV), and Manika Prasad (Stanford University). Other shipboard studies included the collection of 9-m-long box cores from Pigmy and Orca Basins (see map) for measuring contaminant input to the northern Gulf of Mexico from the Mississippi River, part of a project led by Pete Swarzenski (USGS, St. Petersburg, FL). Pigmy and Orca Basins are nearly adjacent; however, Orca Basin has been covered by a thick brine layer for most of Holocene time, producing anoxic conditions at the basin floor. Oxic conditions exist in Pigmy Basin. In addition to studying contaminant-input history, USGS scientists will compare the effects of anoxic and oxic conditions on pollutant sequestration in the two basins. (Clockwise from top left) Bill Ussler (MBARI), Charlie Paull (MBARI), Olya Boldina (Moscow State University), Valerie Hadoux (IMAGES), Jim Flocks (USGS), Tom Lorenson (USGS), and Maria Green-Blum (IMAGES) subsampling a 10-m-long box core. Bill and Charlie are placing sediment in a pore-water squeezer sample mold. The cruise was marked by numerous collaborations among the participating organizations. Working with Louis Geli and Cynthia Labails of the Institut Fran�ais pour la Recherche et la Technologie Polaires, USGS scientists obtained 17 deep (about 10-20 m) heat-flow profiles near the piston-core sites. Results indicate that widely varying geothermal gradients exist across the northern Gulf of Mexico, an important observation for defining the subbottom extent of gas-hydrate stability. The USGS is also working with Catherine Kissel (IPEV) on paleomagnetic studies and with Sabrina Nardozza (Laboratoire des Sciences du Climat et de l'Environnement) on physical-property profiles. The USGS cores collected in the gulf will be archived at Texas A&M University under the guidance of Bill Bryant. Before docking in the Port of Tampa, FL, the Marion Dufresne obtained two cores in Tampa Bay for Terry Edgar (USGS, St. Petersburg, FL) and Deb Willard and Tom Cronin (USGS, Reston, VA), as part of the Tampa Bay project (see first related story, below). A.B. Wade (USGS, Reston, VA) and Hannah Hamilton (USGS, Gainesville, FL) visited the Marion Dufresne while it was in Tampa Bay and orchestrated a series of interviews and videotaping sessions for both national and local news coverage. Research Vessel Marion Dufresne Cores Tampa Bay, Florida September 2002 Gas-Hydrate Research Wells Completed in the Canadian Arctic April 2002 Marion Dufresne Coring in Chesapeake Bay August 1999 Gas Hydrate Studies U.S. Geological Survey (USGS) Institut Polaire Fran�ais, Paul-ƒmile Victor (IPEV) (French-language Web site) Monterey Bay Aquarium Research Institute (MBARI) non-profit research center International Marine Past Global Changes Study (IMAGES) multi-national research organization Laboratoire des Sciences du Climat et de l'Environnement (French-language Web site) Dr. William Bryant - Department of Oceanography Texas A&M University in this issue: next story

September 2002 Mailing List: Sign up to receive monthly email updates: print this issue in this issue: cover story: Gulf of Mexico Gas Hydrate Tampa Bay Coring North Carolina Coastal Erosion Endangered White Abalone Marbled Murrelets Sediment Core Drilling Proposal African Dust Microbiology Tall Ships Gulf of Mexico Teacher Workshop Coastal Louisiana Interview MRIB Makes Headlines U.S. Commission on Ocean Policy Numerical-Modeling Workshop WHFC Employees Farewell Sound Waves Staff September Publications List

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