Hydrothermal Vent

        Basically, an opening on the ocean floor located on or adjacent to the mid-ocean ridge system that spews out super-hot, mineral-rich water that has been heated by contact with molten rock, commonly to between 570° F and 750° F. Author’s Note: In illustration of how far science has come in the last thirty years, the first hydrothermal vent was discovered in 1977. Known as black smokers from inky dark discharged fluids containing high concentrations of minerals, they are found in the Pacific and Atlantic Oceans. Most are located at an average depth of about 7,000 feet in zones of deep sea-floor spreading and form when ocean water circulates in the very hot rocks of the crust, dissolving sulfur, iron, manganese, and copper. As these superheated fluids, attaining temperatures around 750° F, reach a vent and are discharged into the ocean, they often contain dissolved sulfides that are oxidized by chemo-synthetic bacteria that fix carbon dioxide and synthesize organic compounds. The resulting minerals drop out of solution as dark fluids and build up darkish yellow-orange chimneys on the sea-floor. Near the vents, at water temperatures up to 75° F, are highly productive communities comprising animals that use the organic compounds directly or live symbiotically with various chemo-synthetic bacteria. These organisms include carnivores and detritivores, including shrimp and crabs and also some of the most distinctive inhabitants of the Pacific Ocean vent sites: giant clams and long, red tube worms that subsist on the multicolored microbes that coat the chimneys. Note that eyeless shrimp are found only at hydrothermal vents in the Atlantic Ocean.

        But since the early 2000s, geoscientists have found that the black smokers are not the only type of hydrothermal vent on the ocean floor. Located to the side of the Mid-Atlantic Ridge, on a sea-floor mountain named the Atlantis Massif, is an astoundingly beautiful under-seascape of remarkable structures containing an array of delicate flanges, multiple pinnacles, beehive deposits and white carbonate chimneys known as the Lost City Hydrothermal Field. Discovered serendipitously in 2001, its rather romantic name was coined by inspired scientists in honor of the fabled, flooded city of Atlantis made famous by Plato. Unlike the black smokers, the Lost City Field is located away from the spreading rift and is a white forest of concrete chimneys — actually aragonite, brucite (magnesium hydroxide), and silica — that range from spires 20 feet high to giant tubes 200 feet high and 30 feet wide at their mouths and are capped by white, feather-like deposits to cone-shapes to needle-thin tower-like structures. But most importantly, Lost City is an example of a whole new class of vent structures and the product of a major and previously poorly understood geochemical process.

        As geoscientists examined the vent field, they noticed that the area was populated solely by dense mats of filamentous bacteria that thrive on venting alkaline fluids and dissolved gases in the water and not the shrimp, giant clams, and red tube worms characteristic of the black smokers. That significant difference may be attributable to the lower temperature of the discharged water at the Lost City field, which ranges from 160° F to about 200° F compared to the 750° F mineralized water discharged at most black smokers. The temperature difference may result from the way the water is heated beneath the ocean floor. The energy responsible for the black smokers is from hot, molten crustal masses. But the Lost City vents, located in areas of much cooler rock, appear to be heated by chemical reactions rather than by association with magma. Seawater appears to seep into deep faults, joints, and cracks in the rock at the base of the Atlantis Massif, where it reacts with peridotite, whose olivine and pyroxene are easily altered in low pressure, low temperature conditions in the presence of seawater. The chemical reaction produces metamorphic minerals in the kaolinite-serpentine group, gases (hydrogen and methane), and energy that heats the water, which then rises to the sea-floor and emerges from the vents. 

        Of great interest to many oceanographers, the new vent field also has high pH levels, or low acidity. Couple that with another tantalizer, the site also produces high levels of methane, acetate, formate, hydrogen, and alkaline fluids, which the most ancient forms of bacteria are thought to have feasted on billions of years ago And you may have a formula for the origins of life, particularly methanogens, microorganisms that live off methane. Real World Example: In April 2010, a team of British geoscientists discovered the world's deepest undersea hydrothermal vents (black smokers) a little more than three miles below the ocean surface in the Cayman Trench (also known as the Bartlett Deep), which is the world's deepest undersea complex transform fault zone and also contains a small spreading ridge on the floor of the western Caribbean Sea between Jamaica and the Cayman Islands.