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Deep Ocean Basins
Deep Ocean Basins
The deep ocean basin is the part of the ocean floor that lies between the continental margin and the oceanic ridge system. It makes up the majority of the ocean floor and can reach depths of several miles below the surface.
This region includes a variety of underwater features such as abyssal plains, trenches, seamounts, guyots, coral atolls, and hydrothermal vents.
Abyssal Plains
Abyssal Plains
The abyssal plain is one of the flattest, smoothest, and deepest regions on Earth. It lies on the ocean floor between the continental rise and the mid-ocean ridge, usually at depths of 10,000 to 20,000 feet (3,000 to 6,000 meters).
The average temperature of the abyssal plains is about 2 to 3°C (35 to 37°F). Because sunlight cannot reach these great depths, the water stays just above freezing all year round. This cold, stable temperature is maintained by deep ocean currents that circulate water from the polar regions around the globe.
Click on the image above for a more in-depth look.
These vast plains are covered by fine layers of mud and tiny particles that slowly settle from the water above, burying the rough, rocky crust beneath. Even though the abyssal plain may look lifeless, it actually supports many forms of life, including worms, sea cucumbers, and deep-sea fish that have adapted to the cold, dark, high-pressure environment.
Deep-Ocean Trenches
Deep-Ocean Trenches
Deep-ocean trenches are the deepest parts of the ocean floor, forming long, narrow valleys that can stretch for thousands of miles. They are usually found along the edges of tectonic plates where one plate is being forced, or subducted, beneath another. This process is called subduction, and it creates deep cracks in the ocean crust.
Trenches can be extremely deep—some reach more than 36,000 feet (about 11,000 meters) below the surface, like the Mariana Trench in the Pacific Ocean, the deepest known place on Earth.
These regions are dark, cold, and under immense pressure, yet life still exists there. Specialized organisms such as giant amphipods, sea cucumbers, and bacteria thrive in this extreme environment. Ocean trenches are also important for recycling Earth’s crust and triggering earthquakes and volcanic activity near plate boundaries.
Seamounts
Seamounts
Seamounts are underwater mountains that rise from the ocean floor but do not reach the surface of the water. Most seamounts are submarine volcanoes, where magma pushes up through the Earth's crust, creating a mountain beneath the sea.
Seamounts can be hundreds or even thousands of meters tall and often occur in chains along tectonic plate boundaries or over hotspots—most commonly found in the Pacific Ocean. Some seamounts eventually grow tall enough to break the surface and become islands. They are important for ocean life because they create currents that bring nutrients from the deep ocean to the surface, supporting fish, corals, and other marine animals.
Click on the image above for a more in-depth look.
Guyots (Tablemounts)
Guyots (Tablemounts)
Guyots or Tablemounts are flat-topped underwater mountains (seamounts) found in the deep ocean. They were once active volcanoes that rose above the sea surface, but over time, waves and erosion wore down their tops. Eventually, the volcanoes sank back below the ocean surface as the ocean floor moved and cooled.
These flat-topped seamounts are usually found in chains, often near mid-ocean ridges or volcanic hotspots. Guyots are important because they show scientists how the ocean floor changes over millions of years and how volcanic islands can disappear beneath the sea. Like other underwater mountains, they also influence ocean currents and provide habitats for marine life such as corals, fish, and other deep-sea organisms.
Coral Atolls
Coral Atolls
Coral atolls are ring-shaped islands made of coral that form in the ocean, usually around sinking volcanic islands. They begin when a volcanic island emerges from the sea and corals start growing around its edges, forming a fringing reef. Over millions of years, the volcano slowly sinks or erodes, but the coral continues to grow upward, eventually creating a ring of coral where the island used to be. Oftentimes, coral atolls have a calm, circular body of water at their center called a lagoon.
Atolls are often found in tropical oceans and provide important habitats for fish, seabirds, and other marine life. They also protect coastlines by breaking waves and reducing erosion. Coral atolls are fascinating examples of how living organisms like coral can shape the ocean landscape over long periods of time.
Click on the image above for a more in-depth look.
Fun Fact:
Fun Fact:
During the 1940s and 50s, the United States tested nuclear weapons on uninhabited coral atolls in the Pacific Ocean; particularly Bikini Atoll and Enewetak Atoll in the Marshall Islands. This is thought to have been the inspiration for the movie Godzilla. Godzilla was originally supposed to have been a lizard mutated by nuclear radiation, created to symbolize the fear and devastation created by nuclear weapons.
Hydrothermal Vents (Black Smokers)
Hydrothermal Vents (Black Smokers)
Underwater volcanoes near plate boundaries produce hot springs known as hydrothermal vents or black smokers. Hydrothermal vents are openings on the ocean floor where superheated water gushes out from beneath the Earth’s crust. These vents are usually found along mid-ocean ridges, where tectonic plates are moving apart and magma heats the seawater that seeps into cracks in the ocean floor.
The water coming out of hydrothermal vents can reach temperatures of over 700°F (370°C) and is rich in minerals like sulfur and iron. Even though the water is extremely hot, it does not boil because of the intense water pressure at these depths.
Despite the extreme heat, darkness, and high pressure, hydrothermal vents support unique ecosystems that include organisms known as extremophiles.
Extremophiles
Extremophiles
Extremophiles are organisms that can survive and even thrive in environments that would be deadly to most other forms of life. These extreme conditions can include very high or low temperatures, intense pressure, high acidity or salinity, or even complete darkness.
Examples of extremophiles include bacteria living near hydrothermal vents on the deep ocean floor. These bacteria provide the basis for the food chain near hydrothermal vents through a process called chemosynthesis.
Unlike most life on Earth, which depends on sunlight for energy, these bacteria use chemical energy from the hot, mineral-rich water that flows out of the vents. They take chemicals like hydrogen sulfide (which smells like rotten eggs) and combine them with oxygen and carbon dioxide to produce sugars—their food source.
These chemosynthetic bacteria (chemotrophs) form the foundation of the vent ecosystem. Some live freely in the water or on rocks, while others live inside larger animals like tube worms, clams, and mussels, providing them with nutrients. In turn, these animals become food for predators such as crabs, fish, and octopuses.
In this way, bacteria act as the primary producers—just like plants do on land—supporting entire communities of deep-sea life where sunlight never reaches.
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