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The Edge of the Gulf:
Deep Sea Expedition to the Gulf of Mexico

Beneath the Gulf of Mexico, the same oil and gas that heats homes and powers cars, seeps out naturally from the seafloor. Far below the reach of sunlight, these fossil fuels are feeding some of the most unusual ecosystems on the planet.

by Ian MacDonald, Geochemical and Environmental Research Group, Texas A&M University and Andrew Shepard, NOAA's Undersea Research Center at the University of North Carolina at Wilmington

In October 2000, thirty-six scientists and observers completed a productive and exciting program on board this country's premier asset for deep-sea science and exploration. The combination of the deep sea submersible, Alvin, and its support ship, R/V Atlantis, can carry a pilot and two scientists practically anywhere on the ocean floor of the Gulf of Mexico, with a suite of scientific sensors and tools. Fourteen deep-sea dives were conducted at eight locations starting offshore from Texas and ending off Florida. The deepest site visited was almost 11,000 feet deep. The primary expedition goal was to do quality science and at the same time foster public appreciation for the importance of the deep sea.

DSV Alvin can carry people to depths of 4000 meters
(Top) DSV Alvin is America's only deep sea asset capable of carrying people to depths of more than 4,000 meters. Photo: WHOI archives

(Right) Alvin's bow is equipped with a variety of scientific sampling gear. Photo: J. McDonough

Scientific sampling gear on board Alvin

A unique aspect of the expedition was the many partnerships required to fund and support the science, technology, and outreach activities. NOAA's Undersea Research Program (NURP), Minerals Management Service (MMS) and the Department of Energy (DOE) provided support for ship days, sub dives and science. The science team included researchers, students and even an artist from the University of North Carolina at Wilmington, Texas A&M University, Louisiana State University, the University of South Carolina, and the College of William and Mary. Ecology Communications, Inc. provided a television documentary team (show now in production) and support for the expedition web site.

Map of Gulf showing 14 dive site locations
Edge of the Gulf expedition covered 14 dive sites and almost 1000 miles from Texas to Florida.

Tubeworm and mussel bed provides shelter and protection from predators.
Tube worm and mussel bed at the base of the Florida Escarpment hosts a diverse community of small animals seeking shelter and larger predators-oases in the deep sea. Photo: I. MacDonald

During the traverse along the edge of the Gulf of Mexico, fundamental research was conducted on dense assemblages of animals--called chemosynthetic communities--that live off oil and gases that seep and vent from the seafloor. Bacteria thrive at seeps in the deep Gulf. They utilize the chemicals associated with the seeping hydrocarbons for energy and food. The dependence is similar to the way shallow water phytoplankton use light and carbon dioxide. Larger animals, such as mussels, clams and tube worms have evolved a symbiotic partnership with the bacteria similar to what was originally discovered at deep sea hot vents. The Gulf tube worms may live to be 250 years old, making them among the longest living animals on earth. The cold seep communities were first discovered at the base of the Florida Escarpment in 1984. The last dives revisited this historic site to recover experiments and resample and measure the biodiversity of the mussel beds.

Mud furrow carved by deep sea currents at a depth of 2000 meters
Mud furrow is probably carved by strong deep sea currents that cut into the base of Green Knoll, at a depth of over 2000 meters. Photo: I. MacDonald

The investigators searched for evidence to show the existence of abyssal storms. These are intense currents that arise suddenly in the deep ocean with enough power and magnitude to threaten the current generation of deep-sea energy platforms and pipelines, installations that are even now in the planning and construction stages. The team found deep furrows near the base of the escarpment that were clearly being formed during the present day. During the second furrow dive, scientists William Bryant and Eric Scott encountered some of the strongest bottom currents ever experienced by Alvin.


Ice worms are found in gas hydrate beds
Gas hydrates (yellow) are ice with gas trapped inside; exposed beds are accessible to submersibles on the deep sea floor of the Gulf of Mexico. Ice Worms (Hesiocaeca methanicola), a new species only seen in hydrate, were discovered in 1997 by C. Fisher, Penn State University. Photo: I. MacDonald.


Two new sites were explored where gas hydrate occurs at or near the seafloor. Gas hydrate is an ice-like form of natural gas that is currently attracting great interest. Huge amounts of gas hydrate are locked up in the ocean margins--more in fact than at all the known oil and gas reserves combined. Oil companies are interested in learning to tap these reserves as a new source of fossil fuel. But the shallow burial and the relatively fragile preservation of these deposits indicate that they are only temporary phenomena. Increasingly, researchers believe that at times in the Earth's past, gas hydrate deposits have erupted and radically altered the composition of the atmosphere. Gas hydrate may be the world's next energy supply. It was almost certainly a factor in climate change events during Earth's past. The Gulf of Mexico is a wonderful laboratory for studying it first hand.


Base of Florida Escarpment covered with marine snow
Base of Florida Escarpment covered with marine snow. Octocorals attach to steep sides and under ledges to avoid burial. Photo: I. MacDonald

Expeditions to ocean frontiers require dedication and focus on collection of good data, not an easy task in the face of sometimes awesome beauty. Alvin dive 3634, for example, ascended 2,100 ft up a sheer limestone cliff that forms the westernmost limit of the Florida platform. The dive mission was to get a first survey of a marine habitat that is almost completely unknown -- the depths recorded on the dive were quite different from what is shown by existing charts for the region. The dive began at 9,200 ft by climbing up a very steep grade over a soft, silty bottom, pale brown in color. Normally, the water in the deep sea is crystal clear, but at this site particles of sediment were falling like a light snow. There were few animals apart from occasional sea cucumbers. Everywhere we could see the marks of miniature landslides.

Just at the point when it started getting monotonous, a huge black boulder loomed out of the slope. Soon it was joined by other rocks, all coated with a thick drape of the sediment that continued to fall all around the sub. Eventually the individual boulders merged into a continuous wall that went up and up. Up the slope, it became clear that the burial by sediment fall was so intense that practically nothing could live on the rocky wall where normally a variety of attached life forms would be expected. Finally, nearly 2,000 ft above the starting point, a broad ledge appeared. On the underside of the ledge, sheltered from falling sediments and nourished by organic particulates, a bright garden of corals, sponges, and sea-whips hung suspended, swarming with tiny shrimp. Phil Forte, Alvin pilot, was able to hold Alvin steady against the current and creep along the entire ledge while cameras recorded the scene. This incredibly exhilarating dive had to end just as a sense of where to find life in this harsh, incredibly remote habitat was developed.

And in a way, that's where deep sea science is now. The expedition was very successful -- some questions were answered, but even more were asked. NOAA has just declared "a new era of ocean exploration," and provided see funding in 2001. More expeditions to ocean frontiers are planned. This comes at a time when the keys to the past and the energy supplies for the future may indeed lie in the deeper parts of the ocean. It has been a great privilege to participate in an inaugural voyage of this new era. Many thanks to NOAA, MMS, DOE, WHOI and all the institutional sponsors for their part in laying a foundation for continued exploration and understanding of the mysteries and vast resources of the Inter-American Sea, the Gulf of Mexico.

NOAA's Undersea Research Program specializes in placing scientists under the sea using scuba, subs, underwater labs, or remotely using robots or seafloor observatories, to conduct ocean research important to NOAA. The program is a national leader in investigations of coral reefs and beds, deep water reefs, submarine canyons, seamounts, ancient submerged shorelines, water mass boundaries, polar environments and development of advanced undersea technologies. Most of the program's research projects, over 150 each year, are conducted through regional centers, including the NOAA's Undersea Research Center at the University of North Carolina at Wilmington -- responsible for covering 330,000 square miles of territorial sea from North Carolina to Texas.


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Updated: August 22, 2006