7,000 feet under the Sea: LSU scientists take geology to great depths

December 20, 2000

BATON ROUGE -- As LSU researcher Paul Aharon slowly descended into the depths of the dark, cold water of the Gulf of Mexico, the classical music of Vivaldi reverberated in his head. He sank deeper and deeper as the music rose and fell, so consumed by the hour-and-a-half journey that by the time he reached the floor of the Gulf he had to remind himself that he was there to work.

LSU scientist Barun Sen Gupta's journey down was no less dramatic, as marching-band music rang in his ears. "It was magnificent," he said. But upon reaching the bottom of the Gulf, the trip became strictly business. Or rather, strictly science.

Recently, the two LSU geology professors took their research to new depths - 7,000 feet down into the Gulf, to be exact -- to study hydrocarbon seeps, gas hydrates and the single-celled micro-organisms called foraminifera that live in those environments.

The researchers were transported to their underwater laboratory by the deep-sea submersible vehicle named Alvin -- the submarine that took the first pictures of the wreckage of the Titanic in 1986. Alvin, which can dive some 15,000 feet and stay submerged for up to nine hours, is owned and operated by the Woods Hole Oceanographic Institution of Cape Cod, Mass. The sub, just over 23 feet long, 12 feet high and 8 feet wide, can hold one pilot and two scientists per mission, along with their research equipment and a CD player. The pilots like to play classical and marching music for effect.

During the expedition, Sen Gupta and Aharon, along with Joan Bernhard of the University of South Carolina, directed four dives off the coasts of Texas and Louisiana. Sen Gupta and Aharon are working on different, but related, projects. They are also comparing notes with scientists at other universities, including Texas A&M and South Carolina, and research institutes, such as the Wadsworth Center in Albany, N.Y.

Hydrocarbon seeps are areas on the sea floor that leak large amounts of methane gas and/or crude oil. The Gulf of Mexico is unique because it contains both biogenic methane and thermogenic methane gases. Biogenic methane is formed by bacterial activity in sediment. This is the most common way that methane is formed. Thermogenic methane is formed when oil reservoirs beneath the sea floor get too hot and pressurized. When methane reaches the seabed through passages provided by geologic faults, it is either contained in ice forms called hydrates, or released into the water and then into the atmosphere, where it may cause damage to the environment.

Hydrates hold about 160 times more methane than if the gas were in its free form. Gas hydrates form and become stable when water reaches a certain temperature and pressure. As water warms or as pressure decreases, hydrates become unstable and break down, releasing the gas in a process that can be harmful to the atmosphere. Methane contributes to the greenhouse effect 20 times more than carbon dioxide does, Aharon said. If the Earth's oceans warm up as they are predicted to with global warming, increasing amounts of hydrates will become unstable and release methane. The release of gas would contribute to further global warming, and a dangerous cycle would begin.

Aharon's research focuses on this cycle and on what has happened to hydrates in the past. Sen Gupta's research examines foraminifera -- single-celled organisms with shells the size of sand grains. Some foraminifera live in areas where gas hydrates are present. By studying the sediments from the floor of the Gulf, the researchers hope to find the link between ocean changes and hydrate stability and provide a history of gas hydrates and how they affected the atmosphere in the past. The goal of both researchers is to learn about the past and compare those findings with the present to be better prepared for the future.

"We are looking for the connection between present-day environments and past environments," Aharon said. "The present is the key to the past."

By taking cores of sediment from areas where gas hydrates are present, the researchers were able to document the presence of certain chemical markers and certain types of foraminifera that are unique to those environments. In the future, by comparing the chemical markers and the types of foraminifer fossils in other sediment cores with those from their control samples, Aharon and Sen Gupta expect to identify places where gas hydrates once existed but are now absent.

In some of their sediment cores, the hydrates were still intact. In others, spaces existed where hydrates used to be, but the ice forms were gone, which means methane was released into the water and then the atmosphere. Aharon and Sen Gupta hope to explore when and how the gas was released. If their studies show that previous large releases of methane gas correspond with past planetary climatic changes, such as global warming, it could explain why such events took place and whether Earth is in store for more such changes.

"There is a lot of geologic evidence that brief events of global warming have taken place repeatedly throughout the Earth's history, most recently during the past 60,000 years," Sen Gupta said. "Some scientists think that such events may be connected to the release of gas from hydrates."

The researchers said some members of the world's scientific community even speculate that the extinction of dinosaurs could be related to a major climactic change brought on by the release of methane through gas hydrates.

Daniel Van Gent of the LSU Nuclear Science Center, Lorene Smith of the LSU Museum of Natural Science and LSU graduate students Matt Hackworth and Sam Huisman of the Department of Geology and Geophysics also accompanied Sen Gupta and Aharon on the expedition.

The LSU team began its journey aboard Atlantis, the mother ship that carries Alvin out to sea. Atlantis also lowers Alvin into the water, communicates with the sub's crew while it is beneath the surface and hoists it up again when the underwater mission is complete. While under water, Alvin is self-propelled, cruising to wherever its crew directs, which can be difficult because beyond the reach of the sub's lights, it is totally dark under thousands of feet of water, Aharon said. Alvin is also equipped with television cameras and a robotic arm, which Aharon and Sen Gupta used to obtain their sediment cores.

One voyage to the floor of the Gulf to conduct experiments takes about nine hours round-trip, Sen Gupta said. During that time, Alvin's pilot and the researchers are cramped into a tiny compartment. But the effort is worth the experience, he said.

"Once on the Gulf floor, you get so excited and so busy that you forget about the discomfort," Sen Gupta said. "Even though the dives each took nine hours, we always ran out of time."

Alvin is in great demand among scientists who want to conduct research thousands of feet under water, and it has been 10 years since LSU researchers have been able to obtain the vessel for their use. For the 2000 LSU expedition, Sen Gupta and South Carolina's Bernhard had received a grant from the National Oceanic Atmospheric Association to cover their expenses, which included a $30,000-a-day fee for the use of Alvin.

After the LSU team had completed its four dives, it transferred from Atlantis to another ship for the return home. But the ship transfer turned out to be one of the most difficult parts of the voyage.

"We had to transfer from one ship to the other in a little rubber dinghy on a choppy sea," Sen Gupta said. "And because of our underwater samples and equipment, we had to make many trips back and forth. It was a little anxious."

The researchers said it is remarkable how such a trip becomes all-consuming. "While you are on this trip, your life revolves around Alvin," Aharon said. "You forget about life outside the ship and what the LSU football team is doing."
Photos available for download at http://www.geol.lsu.edu/research/submersible

Contact Kristine Calongne
LSU News Service

More news and information available on LSU's homepage at www.lsu.edu

Louisiana State University

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