Hydrothermal vents are also known as “black smokers” and are like hot springs and geysers that are found on land. They form in volcanically active areas, often on mid-ocean ridges, where the tectonic plates are splitting apart from each other and the magma starts to seep through to the surface or very close beneath the sea floor. The ocean water manages to make its way through the pores and cracks in the Earth’s crust and is heated by the magma that lies beneath. The heat encourages chemical reactions that removes the oxygen, magnesium, sulphates and other chemicals that are present in the water. The water begins to become hotter and various metals are released from the surrounding rocks. So, where did they come from and why are they important?

First discovery

First used in 1977 to explore the deep sea, the submersivle Alvin (source)
First used in 1977 to explore the deep sea, the submersible Alvin (source)

38 years ago, in the year 1977, a team of scientists ventured into the ocean in the submersible Alvin. Alvin was the first deep sea submersible that was able to carry passengers, not many passengers (a pilot and two observers) but it was the first of its kind. Today, after a number of different upgrades and reconstructions, Alvin can now reach down to depths of 14,764 ft. 38 years ago these scientists made a discovery at the bottom of the Pacific Ocean. Here, they found vents that were teeming with hot water that were rich in minerals, seeping out from beneath the sea floor. Not only did they find these vents but they also found a number of different organisms that were thriving in a habitat that lacked sunlight. The biological communities that were found by these vents relied on the chemical processes that are a result of the interactions that occur when the seawater meets the hot magma.

What are hydrothermal vents?

Hydrothermal vents occur in geologically active areas of the sea floor that are in the regions of tectonic plates. In these areas, water is able to seep through into the Earth’s crust via cracks and fissures on the ocean floor. On its way down, the water gains minerals and other chemicals collected from the rocks. The water meets that magma that is underneath and begins to heat up, when it reaches a certain temperature it begins expands and rises back up to the surface. Some of the water that rises up first contain minerals that will precipitate out and will then harden onto the edge of the vent, thus beginning to create the upwards structure of the vent. The dark colour of the water that is emitted from the vent earns its nickname of the “black smoker” because it looks like a chimney. The temperature of the water that is being released from these vents can reach up to 400 ⁰C, some temperatures can reach higher than this.

The structures of hydrothermal vents can be characterized by their physical and chemical factors, this may include their temperature, minerals within the waters, and by the flow levels of the water coming out of the vent. They are capable to forming “chimneys” that are up to 55 meters tall. As well as “black smokers” you can also find “white smokers”. “White smokers” release cooler waters that are rich in calcium, barium and silicone, they also form smaller chimneys. However, vents that have cooler waters and weaker flow rates are often referred to as seeps rather than vents.

On the left, a "white smoker" also known as a cold seep. On the right, a "black smoker" also known as a hydrothermal vent (source)
On the left, a “white smoker” also known as a cold seep. On the right, a “black smoker” also known as a hydrothermal vent (source)

What organisms can be found at hydrothermal vents?

Cold seeps and hydrothermal vents are areas that have chemical rich waters that provide energy to sustain the communities found in these very harsh environments. Cold seeps and hydrothermal vents and very different environments and therefore re home to different animals. On land and near the ocean surface, the sunlight provides energy to plants and some organisms which allows them to photosynthesize, creating a primary food source. At hydrothermal vents, many microbes have evolved a chemosynthetic processes to create organic matter by using the oxygen in the sea water to oxidize other chemicals present. Clams, mussels, snails, shrimp and other animals feed on the microbes. Other animals, like tube worms, host microbes on their bodies, providing them a place to live in exchange for nutrients.

Giant tube worm, found by the hydrothermal vents, presenting its red plumes (National Geographic)
Giant tube worm, found by the hydrothermal vents, presenting its red plumes (National Geographic)

Giant tube worms (Riftia pachyptila) can grow up to eight feet long but have not mouth or digestive tract, so they rely on the bacteria that live inside them for their food. The tube worms and the bacteria have symbiotic relationship, the bacteria will convert the chemicals found in the water into organic molecules that the worm can feed on. They have giant red plumes that extend out of their body, these are used to exchange compounds found in the sea water. They have this bright red colour because of the large amount of haemoglobin found in them.

Other animals found at the vents:

  • Annelids
  • Gastropods
  • Crustaceans
  • Large bivalves

Why are hydrothermal vents important?

The discovery of the vents changed the way that people understood haw life can exist on Earth. Organisms that thrive in this area have to withstand freezing cold, darkness, high pressures and toxic chemicals. For this reason, animals here are known as extremophiles because of the extreme nature of their living conditions. The more we learn about the organisms that live here, more possibilities are created for discovering previously unknown metabolic processes and compounds that could have commercial uses.

Hydrothermal vents act as a natural plumbing system, which transports heat and chemicals from the Earth’s interior to help regulate global ocean chemistry. They accumulate large amounts of potentially valuable minerals on the sea floor. A few companies have made plans to make use of the commercially valuable mineral deposits that are believed to be found on the sea floor near the vents. However, the difficulty of mining in deep water near fragile ecosystems have made it impossible for sea floor mining to occur. But, possibly in the future, sea floor mining will be able to occur and the minerals found here can be put to good use.

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