The Deep Ocean

To someone who can’t swim, the “deep sea” may be just above ankle level in the ocean. So what do scientists mean when they refer to the “deep sea”?

The ocean floor is divided into several areas.

The continental shelf extends underwater from each of the major land masses. It’s the submerged portion of the continents. The shelf has features similar to those we see on land, including hills, ridges, and canyons. The shelf varies in size. It may be virtually non-existent off some land masses; elsewhere, it may extend underwater a great distance from shore. The shelf’s average distance is about 64 kilometers (40 mi).

It is beyond the continental shelf that the “deep sea” begins. The shelf ends at a depth of about 200 meters (660 ft.). The continental shelf gives way to the steeper continental slope, which descends about 3,700 meters (12,000 ft.) to the deep ocean basin.

Here, the ocean floor deepens sharply, and its features resemble those on land, only on a much larger scale, with great plains and mountains. In fact, the Earth’s longest mountain range is underwater. Over 56,000 kilometers (35,000 mi.) long, this mountain range, called the Mid-Ocean Ridge system, snakes around the globe.

The Mid-Ocean Ridge marks one of the most geologically active areas on Earth. It is where the planet’s crustal plates are moving apart. It is where new seafloor is being born, giving rise to hydrothermal vents and volcanoes.

Seafloor Geology

Mid-Ocean Ridge

Plate Tectonics

Deep Ocean Chemistry

Creatures of the Deep