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DIVING TO EXTREMES - MISSION FEATURE Text courtesy of researchers Samantha Joye, Ph.D. and Ian MacDonald, Ph.D. The Gulf of Mexico is the longest coast in the US. The gulf is a significant source of energy resouces (oil and gas), and it is an economically important region for marine 
transportation and fisheries resources. Submersibles including HBOI's JOHNSON-SEA-LINK I and II
have allowed scientists to explore and investigate the continental slope of the Gulf of Mexico.
In the past ten years, this work has uncovered life-forms and geological features that
challenge the imagination.
Join @Sea from July 2 - 19, 2001 during an expedition to study of the molecular microbial ecology and biogeochemistry of methane hydrates and brine pools along the continental slope in the Gulf of Mexico. These unique and lightless communities are home to a variety of organisms like seep mussels and tubeworms, supported by large numbers of bacteria. Chemoautotrophic microbes are bacteria that use chemical energy instead of sunlight to make new organic compounds. They form the base of the food chain in these communities. Hydrocarbon seeps, abundant in sulfide and methane, provide a favorable environment for these microbes. They can be present as bacterial mats, or living symbiotically in other organisms to help them live in this environment. 
This project is a collaborative effort between Drs. Samantha Joye (University of Georgia), Patricia Sobecky (Georgia Institute of Technology), Joseph Montoya (Georgia Institute of Technology) and Ian MacDonald (Texas A&M University). During July 2001, this team will be conducting a research cruise to study hydrates and brine pools in the Gulf of Mexico on board HBOI's R/V SEWARD JOHNSON (R/V SJ) using the JOHNSON-SEA-LINK II (JSL) Research Submersible. DIVING TO EXTREMES will be conducted approximately 100 miles due south of Louisiana, where the continental shelf becomes steep, in water depths of 500 - 1000 meters. The shelf is made up of mounds, ridges and valleys formed over millions of years over a vast salt deposit. The expedition leaders will be diving at four stations, Green Canyon 234 (GC 234), GC 185, GC 233 and Garden Banks 425 (GB 425). The brine pool sites are GC233 and GB425 and the hydrate sites are GC234 and GC185. This portion of the Gulf of Mexico is a rich petroleum basin and oil and gas harvesting platforms are common. To obtain access to these sites, we conduct research cruises using the JSL launched from the research vessel twice per day. Two scientists accompany a pilot and engineer on each dive. What is a brine pool? Hypersaline brine pools are a unique feature of this petroleum basin. Brine pools form when warm, salty fluids migrate up through the sediments through fissures in the sediment. So at places where seepage is active, brine fluids with four or five times as much salt as seawater will also escape. The brine is much more dense than sea water, so it pools on the surface after cooling to ambient temperature. 
During this mission the team will visit two brine pools, one which is possibly old and stable, the GC233 brine, and one which is quite young and active, the GB425 brine. The GB425 brine has frequent eruptions of hot fluid and macrofaunal communities are not abundant in this area. In contrast, the GC233 brine has been stable long enough for a dense community of mussels to develop around the pools edge. These mussels, which are common at brine and hydrate sites in the area, live in association with methane oxidizing bacteria. Mussels living on the edge of these pools can exploit the methane dissolved in the brine as long as they can keep their siphons above the salty layer. Click here to see a laser line mosaic of a brine pool which is about 15m across and entirely surrounded by seep mussels. The pool fills a crater in a low mud mound and was probably formed by a violent eruption of gas. Image by Ian MacDonald. What is a gas hydrate? Another exotic occurrence at seeps is a kind of ice called gas hydrate. Gas hydrate forms when molecules of methane become trapped in a cage of water molecules. This can only happen under considerable pressure--but there's plenty of pressure at a depth of 500m. As long as the pressure is maintained, hydrates stay solid at temperatures of 8° C or more--well above the freezing point of water in air. 
During a dive in the JSL in 1997, the keen eyes of HBOI Submersible Pilot, Phil Santos spotted an unusual organism. He and scientist Dr. Charles Fisher (Penn State Univ.), found a new species of polychaete worm living in shallow burrows in the hydrate. The worms had probably been there all along, but had simply escaped notice. That is what can happen when working in an environment where access is so limited and difficult. Methane hydrates represent one of the most important reservoirs of organic carbon on Earth. Methane hydrates are found along continental margins around the world. Hydrates represent a unique extreme environment that could serve as a novel niche for microbial life. Visit @Sea throughout July to follow the fascinating work of this multidisciplinary team of researchers as they dive to extremes. CHECK OUT OUR RELATED LINKS SECTION FOR MORE!  | |
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