Hot springs on the ocean floor were only discovered in the 1970s and are among the most spectacular features of the deep oceans. The hottest of these hydrothermal vents are the famous black smokers with water coming out at temperatures exceeding 350 degrees Celsius.
Due to particles in this water they look like huge plumes of black smoke in the comparative emptiness of the ocean floors. Hydrothermal vents also host some of the strangest ecosystems in the world.
Black smokers are distinguished from similar hydrothermal vents by the temperature of the water rushing out. Most (there are exceptions) have hydrothermal fluid of between 350-400 degrees. White smokers are defined by temperatures of less than 330 degrees so there is obviously a grey area.
Both require two key factors: hot rocks near the surface of the ocean crust and sufficient cracks in the rocks to allow water to circulate beneath the surface. There are also warm water vents, with temperatures below 35 degrees. It is thought these warm vents can eventually develop into black or white smokers.
It is seawater that percolates down through cracks, crevices and pores in the rock and emerges as the black smoker but it changes in composition along the way. It loses some constituents, gains others, and some change.
Sulphates for example usually become reduced to sulphides. These then combine with iron and other metals to form insoluble metal sulphides, which create the characteristic and dramatic ‘smoke’.
Some also remain behind to form solid chimneys on the sea floor. It is the heat of black smokers that allows the metal sulphides to rush out as smoke, rather than being precipitated before the fluid emerges.
Black smokers are found along the spreading axes that wind their way throughout the world’s ocean basins. These are underwater ridges, similar to mountain chains, that occur where two tectonic plates join. Hydrothermal vents rarely occur by themselves and normally a number occur close together over a small area to form a vent field.
The ecology of vent fields is bizarre. Communities form based not on energy from the sun, as we are familiar with, but on the chemicals from the black smokers and other vents. The primary producers, the equivalents of plants essentially, are bacteria that can metabolise these chemicals. Most studied to date are sulphur oxidising bacteria utilising hydrogen sulphide but there are probably other important chemosynthetic bacteria using methane or ammonia in vent fields.
These bacteria support dense communities of very strange animals. So far scientists have discovered giant tube worms, giant clams, and giant mussels. Crabs are common in vent fields as are starfish and shrimps. Over 95% of the species described in vent fields so far have been completely new to science.
We don’t even yet know where all the vent fields and black smokers are located and we certainly don’t know what all the animals living around them are. On average, since 1977 a new hydrothermal vent species has been found every ten days.
Black smokers are one of the most dramatic examples of what lies in the very deep ocean that we had no idea even existed. There are still discoveries being made in the oceans of very new and very strange things. With new species being found constantly and the physical mapping of the ocean basins still underway the seas pretty much are the last real frontier.