Study Guide: Deep Ocean Vents
- Ocean vents erupt out of deep cracks in the ocean floor.
- Ocean vents are hydrothermal (hot water). Other types of hydrothermal vents include hot springs and geysers.
- Ocean vents eject hot, toxic, fluids and gases into the seawater.
- They are often located near regions of tectonic activity.
- Ocean vents create some of the most hostile habitats on Earth, but even here life has evolved to survive.
Ocean vents are a type of hydrothermal vent. Other types of hydrothermal vents include hot springs, geysers, and fumaroles. As their name indicates, all hydrothermal vents are characterized by water (hydro-) and extremely high temperatures (thermal).
Locations
Ocean vents are the result of tectonic activity beneath the ocean floor.
Ocean vents are found in all ocean basins, but most have been found around the Pacific Ocean’s “Ring of Fire,” which also includes active earthquake zones, volcanoes, and ocean trenches.
Ocean vents are found near mid-ocean ridges and volcanic arcs. The molten magma of the Earth’s asthenosphere comes close to the surface.
Mid-ocean ridges form at divergent plate boundaries, where tectonic plates are moving apart from each other. New oceanic crust is formed at mid-ocean ridges. The Mid-Atlantic Ridge runs through the entire Atlantic Ocean. Ocean vents dot the entire underwater mountain range.
Volcanic Arcs form at convergent plate boundaries, where a heavy tectonic plate is sliding beneath a less-dense plate in the process of subduction.
Oceanic crust is destroyed in the subduction zones around volcanic arcs. Volcanic arcs can include volcanoes that rise above sea level, such as Japan’s Ryuku Islands. Others remain below the surface of the ocean. These are called seamounts, or underwater mountains.
Upon contact with the cold, dense ocean, the vent fluid “precipitates” minerals, such as sulfates, sulfides, and quartz. These minerals give ocean vents their characteristic color and shape.
Vent Plumes
As vent fluid is ejected into the ocean, it forms a hydrothermal plume. These plumes can look like smoke, but like volcanos they are actually made of minerals and gasses. Because plumes are hotter than seawater, they are more buoyant, and continues to rise until they reach the same temperature.
As the plume rises and expands, it mixes with seawater and becomes diluted, cools, and is gradually dispersed by ocean currents.
Vent Chemistry
The minerals in ocean vents affect the chemistry of the ocean. At mid-ocean ridges, ocean vents help cool new oceanic crust. At volcanic arcs, they contribute to the geology of the seafloor and create underwater mountains.
Temperatures at vent fields range from below 50° Celsius (122° Fahrenheit) to more than 400° Celsius (752° Fahrenheit)—hot enough to melt lead.
Some ocean vents are rich in oxygen and oxygen compounds (such as sulfates).
The temperature and chemistry of vent fields varies depending on the composition of the rock in each part of the oceanic crust.
Cooling the Earth
Ocean vents help cool the Earth’s interior. Oceanographers and geologists estimate that ocean vents account for 10% of total heat loss from the Earth’s mantle.
Vent Chimneys
Sulfides and sulfates exist in a dazzling array at ocean vents: calcium sulfate, strontium sulfate, zinc sulfide, iron sulfide, copper sulfide, iron sulfide, manganese sulfide. These compounds interact with other elements, including hydrogen, helium, potassium, gold, silver, and cadmium. Vent fluids even interact with sodium and chloride, to form salt.
As ocean vents eject mineral-rich fluids into the ocean, many minerals precipitate (solidify) to form tall, thin vent chimneys are made of copper, iron, zinc, cadmium, silver, and even gold.
As long as they continue to eject fluid, the chimneys continue to grow. Some chimneys can grow 30 centimeters (almost 12 inches) each day, and reach 20 meters (65 feet) tall. Tall chimneys don’t last long, though. The mineral structure is fragile. Powerful undersea currents and pressure cause them to collapse.
Types of Ocean Vents
Ocean vents can be classified as black smokers, white smokers, or snowblowers.
All these ocean vents form in the same way. The differences are caused by the differing minerals they produce.
- Black smokers are the largest type of ocean vent, and eject the hottest fluids. The “smoke” blown from black smokers is a dense cloud of particles, mostly metals such as iron and copper. The metals in the fluid mix with the oxygen in the seawater to form a black cloud.
- White smokers develop over cooler vents. White smoker fluid is more acidic, and their chimneys contain more zinc, cadmium, silver, and gold.
- Snowblower vents develop around low-temperature diffuse flows, often around lava from underwater volcanoes. Snowblowers earn their nickname by ejecting columns of white, fluffy particles. Snowblower particles are not minerals. They are made up of billions of tiny, organic microbes. The heat and minerals present in lava interact with seafloor communities of bacteria and archaea, producing flocculent microbial blooms.
Ocean Vent Communities
Many unique organisms are adapted to life in the harsh environment of an ocean vent. In fact, ocean vents set the highest temperature possible for life to exist—a fiery 121° Celsius (250° Fahrenheit), found on the Endeavor hydrothermal vents on the Juan de Fuca ridge off the coast of Vancouver, British Columbia, Canada.
Most biological communities on Earth need sunlight for energy through photosynthesis.
Organisms near an ocean vent do not always have access to sunlight. These organisms depend on a process called chemosynthesis. In chemosynthesis, microbes convert vent fluids such as hydrogen sulfide into energy (simple sugars), water, and sulfur. Sulfur is naturally a yellow, and many bacterial mats have a characteristic golden color as a result.
These specialized microbes (mostly bacteria and archaea, single-celled organisms similar to bacteria) live everywhere in the vent community. They live on the vent floor. They live inside chimneys. They even live inside animals like tube worms and mussels. These microbes are the basis of food webs in the ocean vent ecosystem. Tube worms, mussels, and clams use the microbes to produce nutrients. Plankton and shrimp eat the microbes. In turn, predators like crabs, fish, jellies, and octopuses prey on these animals.
The deep ocean is often so dark that many creatures do not have functioning eyes. Their bodies are often gelatinous and lightweight, to offset the crushing pressure of the deep.
Ocean vents provide an “oasis” of biological activity on the ocean floor, which is often dominated by abyssal plains. For this reason, ocean vents have one of the highest rates of biomass of any habitat on Earth. Busy, clustered communities of organisms thrive around the vents.
Exploring Ocean Vents
In 1977, oceanographers, led by National Geographic Explorer-in-Residence Robert Ballard, were exploring the Galápagos Rift along the mid-ocean ridge in the eastern Pacific.
The scientists noticed a series of temperature spikes in their data. They wondered how deep-ocean temperatures could change so drastically over such a short distance—from near-freezing to 400°C (750 °F). Ballard and his crew quickly sent cameras to the seafloor to investigate the anomaly.
What they discovered were ocean vents. Fascinated by these undersea features, oceanographers used a submersible to study the vents themselves. They were even more fascinated to discover a diverse, thriving community of living organisms. Until this point, all life on Earth was considered to be dependent on sunlight.
Today, oceanographers use an array of instruments to study ocean vents. Bathymetric maps of the seafloor and interactive maps of ocean currents help them identify hydrothermal plumes rising through the ocean. Plumes may be identified through their temperature, chemical structure, and even their color.