What Lies Beneath

A group of very old tubeworms (Lamellibrachia luymesi and Seepiophila jonesi) living on the same piece of carbonate rock as large colonies of the gorgonian Callogorgia Americana americana, with brittle stars and a galatheid crab crawling on the gorgonians. Credit: Derk Bergquist

When most people think of Louisiana as being unique, they think of Mardi Gras, crawfish and Cajun culture. Few realize that what lies beneath the Gulf of Mexico along Louisiana’s coast is also unique, from the terrain and habitat to the animals living there. And two LSU researchers are diving down some 3,000 meters to explore it.

Researchers Harry Roberts and Bob Carney are combing the most unique continental slope in the world to study some of the most unique animal communities on the planet – all just off the coast of Louisiana.

Roberts and Carney are studying 14 different sites where oil and gas seep up from the bottom of the Gulf. In particular, they are studying the animals that live near these "seeps." These organisms include bacteria that feed on hydrogen sulfide gas, a by-product of the oil and gas seepage; tube worms, mussels and clams that serve as hosts to those bacteria; and shrimp, crabs, fish, snails and starfish that, in turn, feed on the worms, mussels and clams. These animal communities are unique because they only exist near these seeps, and because the bacteria at the base of the food chain are "chemosynthetic," or grow without sunlight.

The large number of oil and gas seeps and the vast amount of salt under the Gulf floor near Louisiana’s coast, along with all the sediment dumped into the Gulf by the Mississippi River, make the continental slope off the coast of Louisiana unique. "It’s the most complicated continental slope in the world, geologically," Roberts said. "There are more seep communities off the coast of Louisiana than most places in the world. The salt, the oil and gas and the sediment create a very dynamic geologic framework."

Along with advancing science, the results of this research could also aid the oil and gas industry, as well as the Minerals Management Service, which gives the oil industry permission to drill and lay pipelines on the Gulf floor. Both the industry and the MMS want to know more about these seeps and the federally protected organisms that live near them in order to avoid drilling and performing other activities in those areas.

The ALVIN submersible begins its descent to 1200m.
Image Credit: Gavin Eppard, WHOI

Roberts and Carney left May 6 for a month-long journey that will take them anywhere from 1,000 to 3,000 meters below the surface of the Gulf. They are diving to the floor of the Gulf in a submersible vehicle known as Alvin, which is operated by the Woods Hole Oceanographic Institute. Alvin, best known to the public for exploring the wreck of the Titanic, is well-known among the scientific community, and is constantly in use all over the world by researchers who are able to pay for its use, either with grant or private funding.

Roberts and Carney received funding for their research through the MMS and the National Oceanic Atmospheric Administration’s Ocean Exploration Program. The use of the Alvin submersible is being funded by NOAA. Since Alvin costs approximately $50,000 a day, the researchers’ use of it for nearly a month is a coup in the science world. Typically, a researcher will get to use Alvin for a few days or a couple of weeks.

As excited as they are about having Alvin for a month, Roberts and Carney admitted feeling some trepidation at being at sea for so long.

While conducting their research, Roberts and Carney will be living on a 280-foot ship with 23 other scientists who are involved in their research and the ship’s crew of 17. When they are not using Alvin, things can get a little boring, they said.

"When you’re not in the sub, you do your nails," Carney joked. "You can process samples and do paperwork, but there is still a lot of time to fill. Eating is a big event."

Both scientists have used Alvin before, so they know what to expect on the trip. They said that trying to exercise on a small ship can be difficult, and there is always the possibility of people on board getting seasick or stir-crazy.

A computer enhanced multibeam bathymetry map of the northwestern and northern Gulf of Mexico continental shelf and slope. The continental slope surface reflects an array of intraslope basins, sites of thick accumulations of sediment, surrounded by higher relief features in the form of ridges and domes that are the expressions of salt masses in the shallow subsurface. Major lease areas established by the Minerals Management Service are superimposed on the image and important features like the Sigsbee Escarpment at the base of the slope are labeled.
Credit: Harry H. Roberts

"It’s not going to be all fun," Carney said.

On most days, the two researchers will be using Alvin to take them down to the bottom of the Gulf. It takes a couple of hours to get to the floor of the Gulf, or the length of two Jimmy Buffet CDs, according to Roberts, who likes listening to music on the way down. But the submersible is small, Carney said, and seats a maximum of three people – two researchers, and a pilot. "Picture three people in the trunk of a Volvo," he quipped. In addition, because of the depths that Alvin is diving, the cabin gets very cold.

There are also a number of safety issues involved with Alvin. Since a complete dive takes a total of eight hours, the crew has to be sure that the weather will be good for that length of time. Alvin cannot leave or return to the surface in bad weather. Also, there are oxygen and carbon dioxide levels to worry about, and the possibility of electrical, navigational and communication failures.

The comforting factor, the men said, is that in the Gulf, the crew is considered "within rescue" by authorities. Sometimes, researchers take Alvin to oceans that are not considered as such.

Drawbacks aside, the researchers said they are excited about the trip and the things they hope to see and learn.

"You get excited because from pre-dive data, it’s clear that there is something you really want to investigate on the bottom, and this is the only vehicle to get you there," Roberts said. "Any trepidation you feel disappears when you begin to dive down, because you’re seeing new things, sampling and taking notes. We will be the first people to ever see and directly sample most of these sites."

"I still get a real trip out of it," Carney said. "It’s delightful to do. I really like to bring new people on these dives. It’s amazing how normally rational people will act on these dives."

"People become awe-struck by the experience," Roberts agreed.

A small orange crab near a few scattered tubeworm individuals at 2180 meters depth in Atwater Valley. Credit: Expedition to the Deep Slope.

Their cruise is being followed and documented on the NOAA Web site at www.noaa.gov. Those interested in the research effort can check the site for daily updates. From the NOAA home page, click on "Ocean," then "NOAA Ocean Explorer," then "Explorations," then look under "2006 Signature Explorations" and click on "Expedition to the Deep Slope."

Roberts, director of the Coastal Studies Institute at LSU and Boyd Professor of marine geology and geophysics/sedimentology, first came to LSU as a student in the 1960s, and has been at the university ever since. Carney, professor of coastal ecology, has been at LSU since the 1980s. Both have been doing research on the Gulf’s oil and gas seeps and the animals that live in those areas since the 80s.

"This project has been a lot of fun and scientifically very productive," Roberts said. "In particular, the early cruises we took to the Gulf floor were fun because it seemed that every dive produced a new discovery. In those days, it was difficult to locate the sites we wanted to study. Today, because of technology that allows you to remotely evaluate the sea floor, the locations of hydrocarbon seeps are about 70 percent predictable."


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