Seabed

Lore & Background

The seabed's structure is primarily determined by plate tectonics. Seafloor spreading creates mid-ocean ridges along the center of major ocean basins, where the seabed is shallower than the surrounding abyssal plain. From the abyssal plain, the seabed slopes upward through the continental rise, slope, and shelf toward the continents. Oceanic trenches, deep valleys, occur along tectonic plate edges, and hydrothermal vents release hot water and chemicals in volcanic areas and trenches. Most of the seabed is covered in layers of marine sediments, classified by origin as terrigenous (from land), biogenous (from organisms), hydrogenous (from chemical reactions), and cosmogenous (from space). Sediments also vary by size, from clays and silts (mud) to sand and boulders. The depth within the seabed itself is called 'depth below seafloor,' measured in meters below seafloor (mbsf). Human impacts on the seabed include exploration via acoustic mapping and submersibles, plastic pollution (much of which sinks to the seabed), and exploitation through deep-sea mining and dredging. The ecological environment of the seabed and deepest waters is collectively known as the benthos, a habitat for creatures.

Reader's Guide

The seabed is a fundamental component of Earth's geography and ecology, covering the floor of all the world's oceans. Its structure, governed by plate tectonics, creates distinct zones from continental shelves to abyssal plains and trenches, influencing ocean circulation and marine life. The seabed's sediment layers record Earth's history, including biological productivity, climate changes, and extraterrestrial impacts. Human activities such as mining, dredging, and pollution increasingly affect the seabed, making its study critical for understanding both natural processes and anthropogenic impacts. The benthos, the ecological zone of the seabed, supports diverse organisms adapted to extreme pressures and darkness. Mapping and exploring the seabed continue to reveal new features, such as hydrothermal vents, and inform resource management and conservation efforts.

Did You Know?

• The seabed is also known as the seafloor, ocean floor, or ocean bottom.
• Most of the seabed is covered in layers of marine sediments, with terrigenous sediment being the most abundant.
• The depth below the seafloor is measured in meters below seafloor (mbsf).
• Plastic pollution is a global phenomenon, and much of the world's plastic ends up in the ocean, with some sinking to the seabed.