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The mission of an international team of scientists on the German research vessel Sonne was to find natural underwater oil seeps and to learn whether they supported chemosynthetic life—life based on chemicals— in the deep waters of the southern Gulf of Mexico. The team, sponsored in part by th National Oceanic and Atmospheric Administration, did find chemosynthetic life and a lot more. NOAA is an agency of the U.S. Department of Commerce.
“We found evidence of asphalt volcanism,” said Ian MacDonald, the scientist from Texas A&M University at Corpus Christi, who led the mission. “It was a new geology, not expected in the deep sea. The flow patterns of the lava-like asphalt deposits indicated the material was once hot and had flowed down slopes for hundreds of feet before hardening. But there are many questions about how the asphalt could be so mobile in such low ambient temperatures.” MacDonald and co-authors presented their findings in scientific paper published in the May 14 issue of the prestigious journal Science.
The target area was the Campeche Knolls, salt diapir structures northwest of the Yucatan Peninsula, where satellite pictures showed persistent traces of floating oil.
“NOAA’s support was critical,” said MacDonald.“ It allowed the United States and Mexican science parties to participate, and it let us acquire the satellite imagery needed to target deep water sites under oil seeps. ” The international team included scientists from the U.S., Mexico, England, China, Russia and Germany.
After the ship mapped the ocean bottom, scientists saw 20 elongated knolls, some more than 1,000 feet above the seafloor. Nine of them lined up perfectly with oil seen in satellite pictures. The science team focused on one knoll they named Chapopote after the Aztec word for tar.
The asphalt was discovered several hours after midnight last Nov. 1, when the research vessel inched ahead with its Ocean Floor Observing System—a sled outfitted with lights, still and video cameras and an altimeter—riding about 10 feet over the ocean floor at the end of a 9,750 foot (3,000 meters) armored cable. Grab samples collected with a huge, steam-shovel like scoop confirmed the material was asphalt. Growing from under its edges were clusters of tubeworms—the signature animal of chemosynthetic communities.
These chemosynthetic communities were mysteriously different from those found at hydrocarbon seeps in the shallower waters of the northern Gulf of Mexico. Sediments there are saturated with oil and gas and microbial processes attack hydrocarbons as a food source, producing hydrogen sulfide (H2S). The H2S feeds symbiotic bacteria living in the guts and gills of tube worms and clams, and those bacteria in turn produce sugar that sustain the tube worms and clams. But most sediment associated with the asphalt was not oily, and samples obtained showed deep-sea mud with no H2S or bacteria.
“Volcanic asphalt as a habitat for chemosynthetic life is new to science and more sampling and scientific analysis is needed,” said MacDonald.
A search of literature for other similar sites produced pictures taken in 1971 from a salt dome 150 miles north of Chapopote. Interestingly, the images showed an asphalt deposit with associated animals including a lone tubeworm, though chemosynthetic life was not “discovered” until nearly eight years later at the Rose Gardens site of hydrothermal vents in the East Pacific.
“For me, Chapopote is an example of how dynamic the deep sea really is,” said MacDonald. “There is no place where life is absent and if life gets the slightest foothold, it will adapt and blossom. Even hydrocarbons are a distant echo of life that existed millions of years ago and now finds its way back to the world. It shows how this planet is alive from top to bottom, and how it always maintains a capacity to surprise us. Efforts by NOAA and the Census of Marine Life promise to produce more surprises in forthcoming expeditions.”
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