Geography of the Ocean Floor

By Sneha Kumar

About the Oceans

The oceans are divided in to four oceans--the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic Ocean.

The Pacific Ocean is the largest and deepest ocean in the world. It covers more than half of the ocean face area on Earth.

The Atlantic Ocean is a relatively narrow ocean compared to the Pacific Ocean. It is half the size of it and is bounded to the east and west by continents.

The Indian Ocean is a bit smaller than the Atlantic Ocean. Unlike the Pacific and Atlantic oceans, the Indian Ocean is almost fully in the Southern Hemisphere.

The Arctic Ocean is the smallest main ocean and is only over a quarter as deep as the rest of the oceans.

Mapping the Ocean Floor

Underwater, the ocean floor is filled with a variety of landscapes including mountains, volcanoes, trenches, and plateaus. Bathymetry is the measurement of the ocean depths and the measuring of the topography or shape. The Challenger expedition was made to study the global ocean floor. It measures every ocean except the Arctic. Today, sonar, satellites, and submersibles allow people to study the ocean floor with more efficiency and preciseness than ever before.

Sonar, Satellites, and Submersibles

Sonar was discovered in the 1920s and is a type of electronic depth-sounding equipment. It works by transmitting sound waves to the bottom of the ocean. Then, a sensitive receiver intercepts the echo from the bottom. After that, a clock measures the time interval to fractions of a second. They calculate the depth by the speed of sound waves in water and the time required for the energy pulse to reach the floor and come back.

Satellites was discovered after sonar and is more precise and accurate. Scientists realized that the ocean floor was not flat. Satellites are able to measure small differences in the ocean floor by bouncing microwaves off of the ocean.

Submersibles are underwater crafts that are used for deep-sea research. They collect data of areas too deep for human reach. They have a variety of instruments from pressure gauges, thermometers, and cameras. Many submersibles are computer controlled and are unmanned. They use sonar, collect organisms, and record video with remote controlled arms.

Ocean Floor Features

The Ocean floor is divided into three major regions. They are the continental margins, the ocean basin floor, and the mid-ocean ridge.

Continental Margins

A Continental Margin is the boundary between a continent and the ocean floor. The Atlantic Ocean's continental margin is covered with thick sediment. The Pacific Ocean's continental margin is narrow and has much volcanic activity and earthquakes.

Continental shelf is a sloping surface extending from the shoreline. They contain important minerals, reservoirs of oil, natural gas, and sand and gravel deposits.

The Continental Slope is the seaward edge of the continental shelf. They contain submarine canyons, and these canyons can extend to the ocean basin floor.

The Continental Rise exists in places where trenches do not exist. This causes the continental slope to gradually incline to become a Continental Rise.

Ocean Basin Floor

The Ocean Basin Floor lies between continental margin and mid-ocean ridge. It is about 30% of the Earth's surface and contains trenches, abyssal plains, and seamounts.

Deep-Ocean Trenches are narrow creases in the floor of the ocean and they are the deepest parts of the ocean. They are mostly located along the margins of the Pacific Ocean. Trenches form at sites of plate convergence where one plate goes under another and plunges into the mantle. The most well-known trench is the Marina Trench, which is the deepest place known on Earth.

Abyssal Plains are extremely flat and deep features. These might be the most flat places on Earth. They have accumulations of fine sediment that buried the rugged ocean floor. They are found in all of the oceans, but the Atlantic Ocean has the most abyssal plains because of the few trenches.

Seamounts are submerged volcanic peaks. They are found on floors of all oceans, however they are mostly on the Pacific Ocean floor. They are volcanoes that have not yet reached the surface to become islands.

Mid-Ocean Ridges

Mid-ocean ridges are found near the center of ocean basins. It consists of a system of mountains that are newly developed. This system is the longest feature on Earth's surface.

Seafloor Spreading is a high amount of volcanic activity that takes place along the crest of the mid-ocean ridge. They occur at a divergent plate boundaries.

Hydrothermal Vents are zones where heated water escape through cracks in the oceanic crust.