What Is A Black Smoker?

In 1949, researchers in the Red Sea discovered hot, highly saline water in pools on the sea bottom. This hot sea water emanated from so-called hydrothermal vents. These vents are similar in many ways to the geysers that are found, say, in Hawaii and other places where there is volcanic activity. Since that time, hydrothermal vents have been widely charted in mid-oceanic regions.

In the oceans, these vents typically form along mid-ocean ridges such as the East Pacific Rise. The vents are also found in the Red Sea where the Asian and African plates are drifting apart. At these junctions two tectonic plates (large sections of the earth's crust) are moving apart and new, young crust is being pushed up from the core.

The water that flows out from underwater hydrothermal vents consists of sea water drawn down into the hydrothermal system close to the volcanic structure by way of faults and porous sediments or volcanic strata, plus some magmatic water released by the upwelling molten rock from the earth's core. In hydrothermal systems on land the bulk of water circulated within the fumarole and geyser systems is mostly ground water that has percolated down into the thermal system from the surface, but it also often contains some water originating from other sources. These proportions vary from location to location.

Water in the deep ocean usually has a temperature of approximately 2-4°C, but water emerges from these vents at temperatures ranging from 60°C up to more than 400°C. Because of the high water pressure at these depths (which can crush a submarine), water can become a supercritical fluid at these temperatures.

At a depth of three kilometres, the water pressure is more than 200 atmospheres (as salt water is denser than fresh water). However the increase in salinity at this depth pushes the water close to its critical point. Therefore, water pouring out from the hottest parts of some hydrothermal vents may be a supercritical fluid, having physical properties between those of a gas and those of a liquid.

Besides being superheated, this water may be extremely acidic, sometimes having a pH value as low as 2.8 - like vinegar, in other words. The subsea fumaroles are also known as chimneys (or smokers) and come in two distinct colours - black or white. The colour reflects the particular chemical contents of the outflows. White smokers usually have a high carbon dioxide content. The effluent is sulphur-rich and can contain large proportions of metals such as zinc, manganese and even gold. Three hundred new marine species have been discovered, with a whole new food chain founded on chemosynthetic archaea at the bottom, supporting diverse life, including giant tube worms, clams, limpets and shrimp.

Microscopic organisms known as Extremophiles, had in 1991, been shown to be able to concentrate metals from seawater. Some observers suggest that some sulphur-oxidizing bacteria of the genera Beggiatoa, Thiothrix or Thiovulum play an active role in this precipitation of metals. It has been suggested that manganese nodules were formed in this way. These nodules are widespread in certain areas of the ocean floor.

Mining of manganese nodules served as a cover story for the incredible attempt by the CIA to covertly raise the sunken USSR submarine K-129, using the Glomar Explorer. The Explorer was a ship built specifically for this secret project by Howard Hughes. The enterprise was known as Project Jennifer, and failed to recover the submarine.

So, Black Smokers (or underwater fumaroles) have a lot to answer for, and extracting gold from sea water economically - well, that is only a matter of time.

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