Hydrothermal vents were first discovered during the Galapagos Hydrothermal Expedition in 1977 funded by the National Science Foundation^[1] 1. “The Discovery of Hydrothermal Vents : 1977 – Astounding Discoveries.” . They are formed by the moving and shifting of earth’s plates, commonly known as plate tectonics, and are found in spreading centers and convergent boundaries. ^[2] 2.  Tunnicliffe, “The Biology of Hydrothermal Vents.” Spreading centers occur when earth’s tectonic plates move away from one another and create a gap in the seafloor, where hot magma wells to the surface to fill the crack^[3] 3.  “Spreading Centre | Geology.”. Convergent boundaries create ocean trenches, and occur when two of earth’s plates collide with one another. Upon contact, the less dense plate is forced underneath the more dense plate in an action called subduction; it is for this reason convergent boundaries are also known as subduction zones^[4] 4. “Convergent Plate Boundaries – Geology (U.S. National Park Service)”.

Hydrothermal vents are a hostile place. The vent chimneys emit fluids that can reach 400°C (752°F) with a pH of 3.2. ^[5] 2.  Tunnicliffe, “The Biology of Hydrothermal Vents.” making it a very hot and acidic environment. Compared to surface ocean temperatures around the globe, that generally range between -2°C to 36.9°C (28.4°F to 98.42°F)^[6] 6. Operations, “NOAA’s Office of Satellite and Product Operations.” with a pH of 8.1, hydrothermal vents seem inhospitable!^[7] 7. “Ocean Acidification | National Oceanic and Atmospheric Administration.

While hydrothermal vents, at first glance,  seem unfavorable to life, vent communities are home to over 236 species. ^[8] 2.  Tunnicliffe, “The Biology of Hydrothermal Vents.” Because light cannot penetrate to the depths of hydrothermal vents locations, the primary producing bacteria, from which the entire ecosystem relies, utilize a process called chemosynthesis. Dense populations of these free-living and surface growing bacteria are responsible for the milky appearance of the water at vents and are the primary food source for filter feeding organisms such as the mussels and clams that live near the vent openings.^[9]9. Felbeck and Somero, “Primary Production in Deep-Sea Hydrothermal Vent Organisms” Unlike photosynthesis that requires sunlight, chemosynthesis uses hydrogen sulfide from the vents to generate energy.

How are Hydrothermal Vents Formed?

Hydrothermal vents form tall pillar-like structures, called chimneys. Chimneys are formed through the deposition and precipitation of minerals when the hot hydrothermal fluid interacts with the cold ocean water. ^[10] 2.  Tunnicliffe, “The Biology of Hydrothermal Vents.”

As we have learned previously, hydrothermal vents are found at spreading centers and convergent plate boundaries. When the plates are moving and cracking, cool ocean water seeps through and is heated by the magma underneath the earth’s crust. As the water continues to heat, a series of chemical reactions occur that remove the oxygen, magnesium, sulfates and other chemicals. As the fluid continues to warm it becomes more acidic and begins to leach metals such as copper, iron, zinc and cobalt  from surrounding rocks. The fluid then rises back up through the cracks in the crust and upon contact with the cool oxygenated ocean water, triggers another series of chemical reactions causing the precipitation of minerals and the formation of chimneys ^[11]11.“Hydrothermal Vents – Woods Hole Oceanographic Institution.”. Depending on the minerals, chimneys can form into two categories, black smokers and white smokers. Black smoker chimneys are formed by iron-sulfide deposits ^[12]12.US Department of Commerce, “What Is a Hydrothermal Vent?” and emit the hottest and darkest plumes ^[13]13. Society, “Deep Sea Hydrothermal Vents.” ,while white smokers are formed by barium, calcium and silicon deposits ^[14]14. US Department of Commerce,“What Is a Hydrothermal Vent?”, and the plumes are generally cooler ^[15]13. Society, “Deep Sea Hydrothermal Vents.”. Vents with even cooler and less intense plume flows are called seeps ^[16]13. Society, “Deep Sea Hydrothermal Vents.”. Interestingly enough, regardless of their scalding temperatures, plumes do not boil due to the intense ocean pressure at 2,500 meters ^[17]9. Felbeck and Somero, “Primary Production in Deep-Sea Hydrothermal Vent Organisms”.

Hydrothermal Vents Vs. Cold Seeps

Often hydrothermal vents are categorized in conjunction with cold seeps. While the two ecosystems share certain characteristics, there are a few differences that make them distinct from one another. As mentioned previously, hydrothermal vents can reach staggering temperatures up to 400°C, whereas cold seeps are far less intense and are only slightly warmer than the surrounding ambient ocean temperature ^[18]13. Society, “Deep Sea Hydrothermal Vents.” . Cold seeps are also considered more stable and have a longer lifespan than hydrothermal vents . In fact, the Riftia pachyptila or Giant Tube Worms found in cold seep ecosystems are among the longest living invertebrates in the world ^[19]19.“Weird Science: Hydrothermal Vents and Cold Seeps | Manoa.Hawaii.Edu/ExploringOurFluidEarth.”.

Perhaps the most significant difference between chimneys and seeps are how chemicals are created in these ecosystems. In cold seep ecosystems the hydrogen, methane, sulfide and other hydrocarbon rich chemicals leach from petroleum, which is created when organic matter is exposed to high temperatures for long periods of time ^[20]19.“Weird Science: Hydrothermal Vents and Cold Seeps | Manoa.Hawaii.Edu/ExploringOurFluidEarth.”. In contrast, the chemicals leaching from hydrothermal vents are created through chemical reactions between cool oxygenated water and hot earth magma.

That’s all for this blog folks, I hope you learned something new and that you have gained a newfound appreciation and interest for an ecosystem perhaps you’d never heard about until now! Make sure to check out our YouTube channel, @LegaSeaTV, to check out our series on hydrothermal vents where we take an even deeper dive into chemosynthesis, vent organisms, and more!

Helena Milazzo

Founder and CEO of LegaSea Ecology LLC

Learn More About Helena