What are hydrothermal vents?
While most would assume that the deep sea is a barren wasteland, there are some areas that are biological hotspots. In 1977 deep sea hydrothermal vents were discovered at a depth of 2500m in the Galapagos rift, at the bottom of the Pacific Ocean. The most surprising feature of this was the wide array of tubeworms (Riftia pachyptila), mussels and clams (Calyptogena magnifica) present on the vents. It has been suggested that the density of organisms present at hydrothermal vents is anywhere from 10,000 to 100,000 greater than that of the rest of the sea floor. Hydrothermal vents are vents which expel extremely high temperature water as well as a vast array of dissolved minerals. The water is super heated by geothermal processes, meaning that hydrothermal vents typically occur in regions of divergent plate boundaries.
The discovery of hydrothermal vents
Hydrothermal vents were discovered with the usage of DSRVs which are deep sea research vessels, which are manned vessels that have robotic arms to collect samples as well as manipulate organisms.
The first site that was explored was the previously mentioned Galapagos rift which is located off the coast of Ecuador, but since then many other areas of vents have been discovered such as the Juan de Fuca ridge and the Gorda ridge.
Black smokers and white smokers
A black smoker is a type of hydrothermal vent that frequently occurs at depths around 2500-300m.
Black smokers are so named due to the thick black smoke that they spew out, this is because the water contains high concentrations of sulphides and other minerals which had been dissolved from the crust of the earth. The water that is expelled from black smokers can reach temperatures ranging from 60°C up to 460°C. The huge temperature increase changes the surrounding water from it’s typical 2°C up to 17°C. The smoke expelled by a black smoker is highly acidic and has caused metal equipment to corrode.
White smokers are similar to black smokers, however the temperature of the water expelled is typically lower, and the plumes are paler due to the presence of other minerals such as calcium and silicon.
The biology of hydrothermal vents.
Surprisingly, hydrothermal vents are extremely productive areas and it all begins with simple bacteria. Chemosynthetic bacteria utilises the sulphide that is expelled as an energy source, over time this develops into a thick covering of bacteria. Over time this attracts more and more different organisms, which again, in turn attracts even larger organisms. This eventually culminates in a hugely diverse ecosystem. Due to the extreme temperature of hydrothermal vents, the organisms found are split into distinct boundaries based on their heat tolerance. Pompeii worms such as Alvinella pompejena can tolerate temperatures up to 80°C and as a result can occupy the inside of vents, whereas mussels such as (Bathymodiolus thermophilus) are less tolerant of the heat and occupy the outer boundaries of the vent where the water is closer to 2°C.
Hydrothermal vents typically have a “lifespan” of around 30 years, this is because over time, the vent flow will slow down. This has a catastrophic effect on the ecosystem that has formed, where some of the more dependent species will die, and as the vent eventually grinds to a complete halt so does the surrounding life.
Another notable feature of life surrounding hydrothermal vents is that they exhibit gigantism, compared to their shallow water counterparts. Some tube worms are capable of reaching heights exceeding 2m. Calyptogena magnifica can range anywhere from 10cm to 26cm in length.
Exploitation of hydrothermal vents.
Due to the vast array of minerals that get deposited by hydrothermal vents, there are propositions to harvest these minerals such as gold and iron. However, substantial testing needs to be conducted to minimise the damage caused to the environment, it is suspected that drilling and other mining processes will cause an increase in the turbidity of the water, this will have devastating impacts on various filter feeding organisms.
The origin of life?
It has been theorised that the conditions produced at hydrothermal vents could have been the areas that initially generated the conditions required for life. This is due to the huge range of chemical reactions that occur in hydrothermal vents. In particular a convincing theory is that due to the presence of ammonia (NH3) and methane (CH4) which did not occur in the earth’s early atmosphere, early amino acids could form higher in the water column due to the presence of clay and cooler temperatures. Some suggest that white smokers have better conditions for emerging life due to their more alkaline conditions.