Seabed

The seabed is the bottom of the ocean. It is also called the seafloor, sea floor, ocean floor, or ocean bottom. The floor of all the world's oceans is known as the seabed.

The structure of the seabed is shaped by plate tectonics. Most of the ocean is very deep, and in these areas, the seabed is known as the abyssal plain. Seafloor spreading creates mid-ocean ridges where the seabed is slightly shallower. From the deep abyssal plain, the seabed slopes upward toward the continents, forming the continental rise, slope, and shelf.

Most of the seabed is covered in layers of marine sediments. These sediments come from different sources: from land (terrigenous), from biological organisms (biogenous), from chemical reactions (hydrogenous), and from space (cosmogenous). They vary in size from very small particles called clays and silts to larger pieces like sand and boulders.

The seabed is home to many creatures and is part of a habitat called the "benthos". Human activities such as exploration, plastic pollution, and mining affect the seabed. Scientists use acoustic technology to map the ocean depths and submersible vehicles to study special areas like hydrothermal vents. Plastic pollution from around the world often ends up in the ocean and can sink to the seabed.

Structure

See also: Seafloor spreading

Most oceans have a similar structure shaped by movements of the Earth's plates and sediments from many sources. This structure begins with a continental shelf, which gently slopes down into the ocean. It then becomes steeper, forming the continental slope, leading to a wide, flat area called the abyssal plain — this is the main part of the seabed. Between the slope and the plain is the continental rise, where sediments flow down.

In the middle of the oceans, there is a high area called the mid-ocean ridge. Along the edges of tectonic plates, deep valleys known as oceanic trenches are formed. In some places, volcanic islands rise from hotspots. Deep ocean water has layers with different temperatures, salt levels, and marine life. The abyssal zone lies above the abyssal plain, while the hadal zone includes the deepest parts of the ocean trenches.

Sediments

Main article: Marine sediment

Sediments in the seabed come from many places, such as bits of land carried by rivers or wind, remains of sea creatures, and chemicals that form in seawater. There are four main types of seabed sediments.

The most common type is terrigenous sediment, which comes from land. This includes materials like clay, silt, and dust that are carried to the ocean by rivers, glaciers, and wind. The next most common is biogenous sediment, made from the hard parts of sea creatures like phytoplankton. Other types include hydrogenous sediment, which forms from chemicals in seawater, and cosmogenous sediment, which comes from space debris like comets and asteroids.

Benthos

The seabed, also called the seafloor or ocean floor, is the bottom of all the world's oceans. It is an important home for many sea creatures, known together as benthos. These organisms live attached to, or near, the seabed and play a key role in the ocean's ecosystem. From tiny sponges to large corals, the benthos help keep the ocean healthy and balanced.

Topography

See also: Bathymetry and Ocean surface topography

Seabed topography, also called ocean or marine topography, describes the shape of the land where it meets the ocean. These shapes are easy to see along coastlines but also exist far underwater. They play an important role in shaping ocean habitats, affecting how ocean currents move and how sunlight reaches different depths.

Marine topographies include many different landforms, from coastal areas like estuaries and shorelines to deeper features such as continental shelves, coral reefs, seamounts, mid-ocean ridges, volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, and abyssal plains. The ocean holds a huge amount of water—about 1.35×10¹⁸ metric tons—and covers much of Earth's surface.

Features

The seabed, also called the ocean floor, has many interesting features. Some of these include flat areas called abyssal plains, underwater mountain ranges known as mid-ocean ridges, deep trenches, and special places called hydrothermal vents.

In places where sediments cover the ocean floor, it is very flat. These sediments come from many sources, such as rivers carrying dirt into the ocean, tiny sea creatures, and movements of sea water. In other areas, especially where the ocean floor is spreading, you can see long straight cracks and vents. Marine life thrives around hydrothermal vents, where special bacteria help create food through a process called chemosynthesis. Shallow areas of the seabed can also host many different kinds of marine life, including corals and fish.

Human impact

Main articles: Deep-sea exploration and Oceanography § History

The seabed has been explored using special submarines like Alvin and, to some extent, scuba divers with advanced gear. Scientists discovered hydrothermal vents in 1977 using underwater cameras. Today, satellites help create detailed maps of the ocean floor, which are very useful for studying the seabed.

Plastic pollution is also a concern for the seabed. In 2020, scientists estimated that the seafloor contains around 14 million tons of tiny pieces of plastic, called microplastic. This pollution varies depending on the slope of the seabed and the amount of plastic on the ocean's surface. These findings highlight the widespread impact of plastic on our oceans.

The seabed holds important archaeological sites, like old shipwrecks and sunken towns. These sites are protected by international agreements to prevent damage and preserve their historical value.