The Ocean Floor

Prerna Bharti Assistant Professor (Guest) B. N College, Patna University

Studying the Ocean Floor

• Sonar- used on ocean surface • Satellite- Seasat and Geosat- used in space

Sonar

• Sound Navigation and Ranging • Scientists send sound waves to the bottom of the ocean by ship. • The sound waves bounce off the ocean floor and return to the ship. • The deeper the ocean , the longer it takes for the sound waves to return. SONAR-FYI

• Measuring Water Depth • Today's oceanographers use sonar instruments to generate a sound signal that is bounced or "echoed" off the sea floor and then recorded on board the ship. The speed of sound in water is 1,500 m per second, four times faster than the speed of sound in air. By carefully measuring the round-trip time of the sound waves and taking into account the variables of temperature and salinity, the depth of the water and the distance to another object can be measured accurately. Seasat • Satellites send images to Earth that measure direction and speed of ocean waves

Seasat-1978 Geosat- Navy Satellite

• Military satellite • Measures height of the ocean surface. • Different underwater features affect the height of the water above them.

The Ocean Floor

• Continental shelf • Continental slope • Continental rise • Abyssal Plain • Mid-ocean ridge • Rift valley • Ocean trench • Seamounts • Continental shelf A • Continental slope B • Continental rise C • Abyssal Plain E • Mid-ocean ridge F • Rift valley F • Ocean trench H • Seamounts D/G

AA B C F G D E

H Continental Margin

• Made up of: • Continental shelf • Continental slope • Continental rise Continental Shelf

• Begins at the shoreline • Continues until the ocean floor starts to slope • Depth can reach about 200 meters Continental Slope • Begins at edge of continental shelf • Continues down to the flat part of the ocean floor • Ranges between 200 meters to about 4000 meters Continental Rise

• Base of continental slope • Made of large piles of sediment Deep Ocean Basin

• Made up of: • Abyssal plain • Mid-ocean ridge • Rift valleys • Seamounts • Ocean trenches Abyssal Plain

• Large, flat area of the ocean floor • Covered in mud and remains of tiny marine organisms • Average depth 4000 meters

Abyssal Plain

Mid-Ocean Ridge

• Underwater mountain ranges • Form where tectonic plates pull apart • Rising magma between the plates creates the ridge Mid-Ocean Ridge Rift Valley • Zone between the plates • In the rift valley, which can be 15 to 30 miles (24 to 48 kilometers) wide, new oceanic crust is being made, which means lots of seismic activity is happening. • Hydrothermal vents were discovered in rift valleys. Seamounts, Guyots, and Reefs

• Conical undersea mountains that rise ≥1000 m above the seafloor are called seamounts – Isolated basaltic volcanoes along mid- oceanic ridges and out in abyssal plains – Chains of seamounts form aseismic ridges • Guyots are flat-topped seamounts, apparently cut by wave action, and commonly capped with coral reefs – Reefs are wave-resistant ridges of coral and other calcareous organisms that may encircle islands (fringing reefs), parallel coastlines (barrier reefs), or rim circular lagoons (atolls)

Rift Valley

Ocean Trench • Huge cracks on ocean floor • Created by oceanic plate pushing beneath continental plate or another oceanic plate • Deep-sea trenches are the deepest parts of the ocean. • The deepest one, the Marianas Trench in the South Pacific Ocean, is more than 35,000 feet (10,668 meters), or almost 6.6 miles (10.6 kilometers) deep. • A Navy-owned submarine, the Trieste, still holds the record for diving to the bottom of the deepest part of

the Marianas Trench, the Challenger Deep, on January 23,1960. Bioluminescence

• Scientists estimate that 90 percent of deep-sea species are bioluminescent . • Bioluminescence is the production of visible light by living organisms. Seamounts

• Mountains of volcanic material • Formed when magma pushes it way through or between tectonic plates • If seamounts build up they can become volcanic islands; Example: Hawaiian Islands • Seamounts are usually 25 miles (40 kilometers) in diameter and can be 10,000 to 15,000 feet (3000 to 4500 meters) tall. Seamounts

• Less than 0.1 percent of the world's seamounts have been explored to learn what species live on them, but many of the species that have been found so far are new to science. • It has been estimated that more than 30,000 seamounts reaching more than 1,000 meters tall are found in the Pacific Ocean. Approximately 800 are in the Atlantic Ocean, and an unknown number exist in the Indian Ocean. • They usually have volcanic origins. Shinkai 6500- Japan

• Shinkai 6500, a Japanese research submarine built in 1989, can work at depths down to 6,400 m. • World's deepest-diving manned research submarine.