Deep-Sea Hydrothermal Vents: New World under the Ocean

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Deep-Sea Hydrothermal Vents: New World under the Ocean

Overview

In 1977, scientists began to search for deep-sea hydrothermal vents, 2,500 to 2,600 meters (8,000 to 8,500 feet) below the sea, using submersible vehicles such as Alvin and Angus. It was on the Galapagos Rift, an area southwest of Ecuador, that the search for hydrothermal vents was first undertaken in an effort to examine the metal deposits surrounding the vents. While exploring these vents, researchers made an amazing discovery. Pictures taken in 1975 revealed the presence of large white clams, but in 1977 an expedition led by Dr. John B. Corliss of the Oregon State University exposed an entire community of animals thriving in the environment around the vents. Other expeditions ensued, as many were intrigued by this unique ecosystem.

Background

Geologists had hypothesized about the existence of deep-sea vents, but it was impossible for them to examine deeper regions of the ocean since the technology did not exist to venture that deep into the ocean. When equipment, such as Alvin from the Woods Hole Oceanographic Institution in Oregon and France's Cyana were developed, deep-sea explorers were able to reach these areas of the ocean. Alvin was capable of descending to depths of 4,000 meters (13,000 feet) and was used in 1977 by Corliss and his team to study the vents on the Galapagos Rift.

These vents were first proposed to exist in 1965 by geologists like Harry Hess and Robert Dietz, as a part of the expanding theory of plate tectonics. In this theory there are 13 semi-rigid plates making up the Earth's crust, which float on the fluid asthenosphere or mantle. The constantly moving plates push together and pull apart, shaping the Earth's surface for billions of years. Individual vents are not thought to last more than 60 years, but the phenomenon of hydrothermal venting is believed to predate life on Earth and may have existed for 3.5 to 4 billion years.

Hydrothermal vents are often found on the mid-ocean ridge, the most volcanically active continuous zone on the Earth's surface. Over 60,000 kilometers (37,282 miles) long, the mid-ocean rift is the largest feature of the Earth's surface and extends from the Arctic Ocean to the Atlantic and crosses the Pacific Ocean to the west coast of North America. A rift is a giant spreading center where tectonic plates are pulling away from one another. As the plates spread apart, hot magma rises up to create new crust. The new crust hardens as it comes into contact with the cold ocean water, fissures develop, and hot water trapped within the crust is released. Water seeping through the ocean's crust becomes heated when travelling through the warm interior of the Earth. The warm water rises and makes its way back into the ocean through the cracks found along zones of tectonic activity. Created along crests in the mid-ocean rift, vent fields form linear zones that can be a few kilometers long and 100 meters wide. Water exiting the vents is rich in minerals and can be as hot as 400 degrees C (752 degrees F), but cools rapidly as the hot water mixes with the cooler seawater. Minerals and sulfides precipitate out when the warm water exits the vents and creates the appearance of billowing white or black smoke. These precipitates accumulate, and create chimneys around the vents.

The vents found on spreading centers in the Galapagos are characterized by hot spewing water and white or black plumes, but vents in areas of convergence, where plates come together, do not have water velocities or temperatures high enough to create these spectacular visuals. Along areas of convergence, such as the Oregon subduction zone located off the coasts of Oregon and Washington, are vents similar to those at spreading centers. More subtle and difficult to detect, these vents are characterized by radon anomalies and elevated concentrations of methane gas.

Impact

The findings of the 1977 expedition prompted the National Science Foundation and the Office of Naval Research to complete a more thorough examination of the hydrothermal vents in 1979. A team of scientists led by geologist Dr. Robert Ballard once again used Alvin to descend to the depths of the Galapagos Rift. What they discovered was truly remarkable. Large white clams, Calyptogena magnifica, that were a foot (0.3 meters) long and large tubeworms, Riftia Pachyptila, that were as much as two meters (6.5 feet) long were seen. Living in basally closed tubes, the worms with their bright red plumes were clustered around the vent openings. Also observed were a mytilid mussel and smaller alvinellid worms, including the pompeii worm, Alvinella pompejana. The area was home to scavenging crabs, such as Bythograea thermydron, and a bythitid fish that was seen with its head down in the vents, presumably feeding. Species of shrimp, limpets, and whelks were in the thickets created by the masses of the worm Riftia and in the vents themselves. These animals are endemic to the vents and do not exist outside the vent fields; indeed the areas surrounding the vent fields are sparse and barren in comparison. Octopus that feed on the clams and mussels may venture into the vent fields, but are not endemic to the vent environment and are the exception. Elevated temperatures at the vents as well as the chemistry of the water make them unsuitable to other marine life, where vent animals have uniquely adapted themselves to this toxic environment.

Sunlight is unable to penetrate so deep into the ocean, and the creatures living around the deep-sea vents survive in an environment devoid of solar inputs. Previously, it had been thought that solar energy and photosynthesis were the basis for all life on Earth; the discovery of the vents challenged that view. Instead, the animals living in the vent fields depend on the energy from the Earth, and a process called chemosynthesis to survive. Living in the vents, and in dense mats surrounding the vents, bacteria oxidize hydrogen sulfide or methane and use the energy to create organic carbon from carbon dioxide. Serving as primary producers in these ecosystems, bacteria are the source of food for primary consumers like the clams, mussels, and worms.

The large white clam and Riftia use symbiotic relationships with bacteria to derive their nutrition. Bacteria have been found in the gills of the clams and in a part of Riftia called the trophosome. Concentrated in the trophosome, bacteria live on sulfides and oxygen transported to this organ by specialized hemoglobin in the worm's blood. In turn, the worm can digest these bacteria. Some alvinellid worms also use symbiotic relationships and are covered by hair-like strands of bacteria, which produce eurythermal enzymes that can withstand dramatic temperature changes and serve to protect the worm from the extreme temperatures experienced at the vents.

The discovery of the vents and the vent ecosystems is significant for many reasons. Animals and bacteria found at the vent sites provide researchers and industry with new concepts and could help develop technology that may help improve our quality of life. Enzymes produced by the bacteria might be used to dislodge oil inside wells, convert cornstarch to sugar, and speed up biological and chemical reactions, possibly useful in other industrial processes. The enzymes can withstand high temperatures, toxic chemicals, and total darkness, and genetic engineers hope to culture bacteria that could decompose toxic waste. Potentially important in the development of new drugs and medicine, vent creatures continue to be investigated.

Rich in metals such as copper, zinc, iron, and gold, the vent chimneys are of interest to the mining industry as well, but the exploitation of this resource is the subject of debate. Some question the ability to safely mine the vents without damaging the unique ecosystems. Despite this, deep-sea vents continue to be of interest to industry, as sulfide ore deposits at the vents might be used when terrestrial resources have been depleted. Sulfide ore is economically important as this class of minerals includes ores of metals such as lead, copper, and silver.

The exploration of extreme environments deep in the ocean also gives researchers an opportunity to develop methods for work in places like Mars, and other dangerous environments. Remote technology and photography are used in deep-sea exploration, along with robotic arms and other specialized parts. Deep-sea vehicles are equipped with advanced sampling devices just as those on Mars might be and give researchers an opportunity to become more familiar with this kind of technology.

Methanococcos jannaschii, a unicellular, microscopic and chemosynthetic organism, found at a vent on the Eastern Pacific Rise in 1982, was confirmed to be part of a newly recognized third domain of life call Archaea by Dr. Carl Woese and others at the University of Illinois. Previously just two domains of life were recognized: 1) Bacteria and 2) Eukaryota. Archaea do not have a nucleus, but one half to two thirds of the genes are unlike anything else on Earth and distinguishes them from the other domains of life. Archaea are believed to most closely resemble the organisms contended to be the first forms of life on this planet.

Important for their potential commercial and scientific value, hydrothermal vents also play an important role in the regulation of the temperature and chemical balance of the oceans. Geochemists, such as John Edmund, have proposed that all the world's oceans circulate through the crust once every 10 million years. When seawater circulates through the crust, magnesium and sulfates are removed, while calcium, potassium, and gases such as hydrogen sulfide and methane are added. Previously it was held that the chemical balance of the oceans was determined by run-off from the continents, but now hydrothermal infusion, or circulation, and continental run-off are considered equally important in this function.

Vent ecosystems continue to be of interest as they provide insights about the origin of life on Earth. While some believe the bacteria thought to be the origin of life arrived on meteors from outer space, called the Panspermia theory, others believe the hydrothermal vents at the bottom of the ocean may be the origin of life on Earth. Useful in the study of life on Earth and life elsewhere in the universe, vents ecosystems are unique. The uncovering of an ecosystem that is based on chemosynthesis and geothermal energy is tremendously important. It challenges the traditional thinking about the physical parameters that will support life and opens new doors for speculation.

KYLA MASLANIEC