The Fluid Flows Around Them: Deep-Sea Worms Affect the Architecture of Black Smoker Chimneys

*Embargoed for release until 6 p.m. EST March 30, 1995

Contacts: Patti Parisi, MBARI--(408) 647-3799 Robert Irion, UC Santa Cruz--(408) 459-2495

For Comment: Terri Cook--(408) 458-9022 Dr. Debra Stakes--(408) 647-3710

PACIFIC GROVE, CA--Deep in the northeast Pacific Ocean, at 2,200 meters below sea level, scientists exploring a hotsprings area along the mid-ocean ridge have found evidence that tube worms have a hand in how "black smoker chimneys" evolve. In the March 31 issue of the journal Science, researchers Terri Cook and Dr. Debra Stakes of the Monterey Bay Aquarium Research Institute (MBARI) show that tube worms--surviving on toxic chemicals--affect the architecture of metal sulfide structures along the Juan de Fuca Ridge.

The mid-ocean ridges are the earth's spreading centers, where the outer layer of the earth's rocky crust is created. As the seafloor spreads away from the ridge, molten rock from deep within the earth continually infills the space left behind. Seawater cools the molten rock that will form new seafloor. As it does, however, the water chemistry changes dramatically by heating and dissolving metals such as iron, copper, and zinc, while becoming rich in hydrogen sulfide. Under the immense pressure of thousands of feet of heavy water column, these hot toxic fluids upwell through cracks in the ocean floor and spew "smoke" charged with mineral particles. These hydrothermal vent fluids are the lifeblood for bizarre creatures such as the tube worms.

Hydrothermal vent sites were first discovered at a spreading center near the Galapagos Islands in 1977 by researchers (including coauthor Stakes) using the submersible ALVIN. The researchers saw biological communities living and thriving in what terrestrial organisms would consider very hostile conditions, such as "rainstorms" of chemicals and the lack of sunshine, oxygen, or food. Scientists were amazed to discover that many species of clams and worms survive on toxic hydrogen sulfide that spews out of the cracks in the seafloor.

As the metal sulfide particulates accumulate, they form structures that look like smokestacks or a pipe organ, pumping out the acidic fluid. Scientists noticed that some of the animals liked to live directly on the walls of the structures to catch the downpour of food. Until now, however, researchers did not know that the biological communities actually play an important role in how the structures grow.

The study reported in Science is based upon samples from the Endeavour Segment, located about 500 kilometers west of Seattle. What is unusual about the black smoker deposits in this location is their enormous size and volume. For example, Godzilla, the largest sulfide edifice reported in the Pacific, is almost 15 stories high.

"Mid-ocean ridge sulfide deposits have been studied since 1979, and scientists have commonly seen tube-worm remnants in deposits, but they could only sample structures like Godzilla by using the manipulator arm on a submersible," said Terri Cook, coauthor of the report and a graduate student at UC Santa Cruz. "Geologists could reach out with the arm and break off or pick up chunks of rock from the top or bottom of the structure's wall, but they had no access to the interiors."

The metal sulfide structures grow up and outward like trees, so access to the interior is crucial in order to see its stratigraphic layers (like a tree's growth rings) to tell how it has evolved over time. Dr. Debra Stakes, coauthor and marine geologist with MBARI, has developed an innovative submersible drill that can penetrate the walls of the structures and remove solid, intact cores. The coring device is revolutionary because it allows high-speed diamond-bit coring to be accomplished by a submersible like the ALVIN or even a remotely operated vehicle. The coring tool's ability to selectively remove oriented cores from different levels of the black smokers allowed Cook to unravel the sequence of events.

"We were able to take samples vertically along the structure, and to go into the structure to look at the time series as it grows outward," said Dr. Stakes. The 1991 expedition took place during a National Science Foundation-sponsored cruise on WHOI's Atlantis II using the submersible Alvin. The prototype coring device that was used on the cruise proved successful on its maiden voyage to recover the sulfide cores across the complex wall structures. "For the first time we can not only see that biogeological interactions exist, but we can see when and how the chemicals and minerals interact with the creatures," said Dr. Stakes.

Dr. Stakes recovered three cores that were chock-full of the tube structures. After making thin sections from the cores, Cook noticed that the minerals in the concentric rings changed over time.

When the minerals seeping around the worms became too hot to bear, the worms would die or abandon the structure in search of a cooler habitat. The worms (and their symbiont bacteria) may actually help form metal sulfides from the hydrothermal fluids, ultimately transforming their casings into small conduits for the hot fluids. Initially, minerals such as low-temperature barite and jelled amorphous silica fill in the pores of the chimneys all around the worms. With increased infilling, the chimneys cook at higher temperatures and become either iron or zinc sulfides. "It is at this middle temperature stage that the worms probably take off because it is too hot for them to survive," said Cook.

The chemical replacement changes the original barite of the worms' tubes to concentric rings of sulfide. Finally, at the highest temperatures of about 350 degrees Celsius, chalcopyrite (copper- iron sulfide) forms and the wall recrystallizes, eventually erasing evidence that the worms influenced the structures' growth.

Like coral reefs grow around organisms, the hydrothermal vent structures grow around the worms. Stakes and Cook often call the structures "sulfide reefs" as an analogy. The worm tube structures change the way fluids circulate through the walls and control the pattern of mineral deposition. "It's amazing to me that something as small as these worms can influence a structure as large as Godzilla," said Cook.

What is still unknown is which was there first: the barite or the worms? Based on earlier papers, Cook believes that the worms somehow aid in the deposition of barite; and that bacteria living within the worms convert that barite to iron sulfide. "The next step is for biologists and geologists to work together to try to document the biological mechanisms for the evolution of these minerals."

Editor's notes: The Monterey Bay Aquarium Research Institute is funded by the Packard Foundation of Palo Alto, California. The report in Science is part of Terri Cook's master's thesis from the Earth Sciences Department at UC Santa Cruz. Photos and graphics of the coring device, the structures, and the worms are available from Patti Parisi at MBARI.

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