What are hydrothermal vents?
Black smoker at Logatchev (MAR)
© Universität Bremen 2004
Hydrothermal vents and their exotic fauna were first discovered on the Galápagos Rift in the Pacific as recently as 1977!! Vents are found on mid-ocean ridges and back-arc basins, which are deep-water volcanic chains. One of the most striking adaptations of vent animals is their association (symbiosis) with microogranisms that use the chemical energy found on the vent fluids for the production of organic matter.
The surface of the Earth is composed of a series of rigid plates that move in different directions. As two adjacent tectonic plates are pulled apart, hot, melting rock from deep in the Earth\'s mantle rises towards the surface. Lava erupts onto the ocean floor, forming the new oceanic crust. This process creates volcanic submarine mountain chains called the mid-ocean ridges. This is where hydrothermal vents are found.
© Illustration by E. Paul Oberlander, WHOI
At the ridges, seawater penetrates into the crust through cracks. The cold seawater reacts with the hot rock close to the magma chamber feeding the ridge. The temperature exceeds 350°C. At this temperature, metals and sulfur from the rocks are dissolved and incorporated in the fluid. This hydrothermal fluid rises back to the seafloor charged with sulfide, hydrogen, methane, manganese and metals, while oxygen and magnesium are absent. When the superheated hydrothermal fluid contacts the surrounding cold and oxygen-rich seawater, its dissolved metals and sulfide come out of solution (precipitate). The emerging fluid is then charged with metal particles and appears as dense black smoke (hence the term “black smokers” often used when describing vents, although smokers can also be white, grey or clear depending upon the material being ejected). These particles are deposited to the seafloor, forming the chimneys of hydrothermal vents, which can reach up to 40 m in height!
Hydrothermal vents were first discovered in 1977 on the Galapagos Rift in the Pacific. But it was in April 1979 when the submersible Alvin was to dive for the first time in search of hydrothermal vents. Bill Normark, from the US Geological Survey, and Thierry Juteau, a French volcanologist, were aboard Alvin for the dive with pilot Dudley Foster. What they found was spectacular: chimneys with black smokers and exuberant oases of exotic animal life in the dark depths of the ocean. This remarkable discovery was totally unexpected - imagine their surprise! Weird and wonderful creatures were thriving in dense communities and it was a complete mystery as to what these animals were using for an energy source in the absence of sunlight, and in the presence of the toxic, high temperature conditions at the vents. Scientists had so much to learn......
© Photo by Dudley Foster, WHOI
Know Vent Locations (So Far……)
Since the first discovery of hydrothermal vents, many other vent sites have been found along mid-ocean ridges in the Pacific, Atlantic, Indian, Southern and Arctic Oceans, and many more are yet to be discovered as we extend our exploration to remote locations. The locations of those active vent sites that have been discovered, may of which have been studied with respect to their fauna, are marked on the map below. A number of new vent sites have been discovered during the course of the ChEss programme including those on the south Mid-Atlantic Ridge, on the Arctic Ridge, in the Southern Ocean, around New Zealand and on the Cayman Rise (the deepest known vent to date).
What animals live there?
1) Bathymodiolid mussels, 2) Riftia tubeworms, 3) Rimicaris shrimp. © Desbruyères, Ifremer/Atos/Ventox
Over 300 new species of animals have been discovered at vents from a number of different animal groups. Many are exclusive to these ecosystems and would be unable to exist outside these systems.
There are differences in the composition of the animal communities found at the different vent sites. For example, the vents in the East Pacific are dominated by giant tubeworms (Riftia), large white clams (Calyptogena magnifica) and mussels (Bathymodiolus). In the Atlantic, however, the vents are dominated by dense aggreations of shrimp and mussel beds. The recently explored Indian Ocean vents also had some surprises to offer...while most of the fauna is related to the animals in the Pacific, the dominant species is the common shrimp Rimicaris from the Atlantic !
One of the most striking features of the exotic animal communities that are found at hydrothermal vents, is that they are sustained by chemoautotrophic bacteria. Metabolic processes of any living organism require a source of energy and a source of carbon for the production of organic compounds which are the base of life. Until the discovery of hydrothermal vents, photosynthesis has been the best known metabolic process for the sustainment of life on earth. Photosynthesis uses light as the source of energy and CO 2 as the inorganic source of carbon. In chemoautotrophy, the source of carbon is again inorganic (CO 2), but the source of energy is chemical, obtained from sulfide or methane. The vent animals are therefore independent of sunlight, and for this reason it has been suggested that hydrothermal vents could have been the location for the origin of life on our planet.
© Lutz, Rutgers University
One of the best examples of symbiosis between a vent animal and the bacteria that sustain it’s life is that of the giant tubeworm. Giant tubeworms (Riftia) can reach upto 3m in length – particularly amazing as they have no mouth, stomach, intestine or anus! They survive only as a result of the symbiotic relationship they have with chemoautrophic bacteria. The plume of the worm is a bright red structure owing to it being filled with blood. It has the ability to uptake oxygen and carbon dioxide in seawater and hydrogen sulphide eminating from the hydrothermal vent. The worm then transports these ingredients in its blood to the a region further down the body called the trophosome. The trophosome is home to the billions of bacteria that act to sustain the life of the worm. They use the ingredients to produce organic carbon that then nourishes both the bacteria and the giant tubeworm. Clever eh?!
Dive with us to a vent
It's 07h45 in the morning. You are on board Research Vessel Atlantis in the middle of the ocean. Today, you will be diving to explore hydrothermal vents and their exuberant fauna in a research submersible. You had your dive briefing last night and have the notes of your tasks in your notebook. Although the submersible has a torpedo shape, the living area where you and the pilots will be is a sphere made of titanium. The combination of the spherical shape and the titanium material is the best option to resist the increasing pressure that the sub will experience as you dive to the bottom. Pressure will increase by 1 atmosphere every 10 meters, so if you go to a hydrothermal site 2500 meters under the sea surface, the external pressure will be ~ 250 atmospheres!