Seabed

The seabed is the bottom of the world's oceans. It is also known as the seafloor or ocean floor. This vast area is a vital part of our planet's structure. The shape of the seabed is governed by plate tectonics. These are the movements of the Earth's large crustal plates. The seabed provides a habitat for living creatures called the benthos. This term refers to both the seafloor and the deepest waters.

The structure of the seabed changes as you move away from land. It usually begins with a continental shelf. This is a relatively shallow area near the coast. Next, the seabed drops off into the continental slope. This is a steep descent into the deep ocean. At the bottom of the slope, a gradual descent called the continental rise often forms. This rise is caused by sediment cascading down the slope. Beyond this lies the abyssal plain. This is a vast, topographic plain that makes up most of the deep ocean.

Deep in the ocean, the seabed features even more dramatic landforms. Mid-ocean ridges are massive, mountainous rises located along the center of ocean basins. These ridges are created by seafloor spreading. Along the edges of tectonic plates, you can find oceanic trenches. These are deep valleys formed by mantle circulation. Some areas also feature hydrothermal vents. These vents release extremely hot, high-pressure water and chemicals into the freezing ocean.

The seabed is covered in layers of marine sediments. These materials are classified by where they come from. Terrigenous sediment is the most abundant type. It comes from land through erosion by rain, rivers, or glaciers. It can also arrive as dust or volcanic ash blown by the wind. Biogenous sediment is produced by living organisms. When tiny organisms like phytoplankton die, their shells sink to the bottom. If these shells make up at least 30% of the sediment, it is called an ooze.

There are two main types of these biological oozes. Calcareous oozes are made of calcium shells from organisms like coccolithophores. These are only found above depths of about 4,000 to 5,000 meters. This is because calcium dissolves at greater depths. Siliceous oozes are made of silicate shells from organisms like diatoms. These shells can build up very slowly. They might accumulate at a rate of only 1 mm to 1 cm every 1,000 years.

Other sediments come from chemical and space processes. Hydrogenous sediment forms from chemical reactions in the seawater. For example, manganese nodules form when metallic elements precipitate from cooling water near hydrothermal vents. These nodules contain metals like manganese, iron, and cobalt. Cosmogenous sediment is much rarer. It consists of space debris, such as pieces of comets or asteroids, that have impacted Earth.

Sediment size also tells us about the ocean environment. Particles range from massive boulders to tiny clay. Larger grains like sand and pebbles sink quickly in high-energy water. Small grains like silt and clay sink slowly. They settle in low-energy areas where the water is not moving quickly. This relationship between grain size and water movement helps scientists understand the history of the seafloor.

Humans interact with the seabed in several significant ways. We use acoustic technology on ships to map the depths of the ocean. Submersible vehicles allow researchers to study unique ecosystems like hydrothermal vents. However, humans also impact the seabed through exploitation. This includes deep-sea mining for minerals and dredging sand for construction. Plastic pollution is another major issue. Because waterways lead to the ocean, much of the world's plastic eventually sinks to the seabed.