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The deep sea is the largest habitat on Earth.

Despite the low temperatures, extreme ambient pressures, absence of sunlight and low resource availability, it supports a rich abundance of life in an array of unique ecosystems.

HYDROTHERMAL VENTS AND COLD SEEPS

A 60,000 km underwater mountain range stretches around our planet, formed as the plates that make up the Earth’s crust move against, or apart from, each other. In these areas, seawater seeps into cracks in the seafloor, heating up as it meets molten rock beneath the crust and then rising again to gush out of seafloor openings. These are called hydrothermal vents. The water that emerges from them can reach temperatures of 400 °C and is extremely rich in minerals. Cold seeps are similar to hydrothermal vents as they also occur in tectonically active locations, but they emit hydrocarbon-rich fluids.

Credit: NOAA

ABYSSAL PLAINS

Abyssal plains cover over half the ocean floor, usually between depths of 3,000 to 6,000 meters. They are among the least explored ecosystems on Earth. Potato-sized polymetallic nodules litter the surface of the abyssal plain, formed over millions of years from metals such as iron, copper, cobalt, manganese and nickel precipitate from seawater. These nodules provide a mosaic of hard substrate for a variety of organisms such as corals and sponges, and support diverse deep-sea communities. Nodules also host a vast array of microbial communities that play a critical role in nutrient and carbon cycling.

SEAMOUNTS

Seamounts are underwater mountains that rise from the seabed without breaking the surface. They are biodiversity hotspots in the vast ocean that swirls around them, each one acting like a unique oasis in the desert.

Seamounts affect ocean circulation and mixing, resulting in nutrient upwellings that stimulate phytoplankton growth, which in turn supports a wide array of marine life. The exposed rocks of seamounts swept clean of sediments by ocean currents are colonized by sessile organisms including cold-water corals and sponges, which globally host more than 1,000 different species including shrimps, crabs, worms and brittlestars.

As well as providing a source of food for an abundance of ocean creatures, seamounts are a spawning ground for numerous species of fish. Many ecologically and commercially important species aggregate around them, including tuna, marine mammals, sharks and seabirds.

Because many of these “underwater islands” are located in remote surroundings, studies are continually finding previously unknown and endemic species. Seamounts are among our world’s greatest biological treasures.

DEEP WATER COLUMN 

The deep water column, from 200 meters below the surface down to the seafloor, accounts for more than 95% of the volume of the ocean. It is vital to many of Earth’s regulatory processes, including nutrient cycling, carbon cycling and storage, and heat absorption. The ocean has absorbed over 90% of the excess heat generated by the burning of fossil fuels; much of this heat has been transported to the deep by ocean currents.