The Ocean Floor

1. The Ocean Floor Earth Science Ch. 14

2. 14.1 The Vast World Ocean • 71% of Earth’s surface is covered by ocean water • 97% of the Earth’s water is salt water found in the oceans • Divisions of the World Ocean • Pacific: largest and deepest • Atlantic • Indian • Arctic • Bathymetry: measurement of ocean depth and identifying the topography of the ocean floor

3. Study of the Ocean Floor • Sonar • Use of sound waves to determine the depth of the ocean floor. • Satellites • Used to determine the size of features on the ocean floor using microwaves • Submersibles • Small underwater crafts used for deep sea research • Contain equipment to collect information about the ocean floor.

4. Sonar

6. 14.2 Ocean Floor Features • Continental Margins • Atlantic Ocean • Very wide • No plate boundaries so there is very little tectonic activity • Pacific Ocean • Very narrow • Nearby plate boundaries causing features such as faults, subduction zones, earthquakes, and volcanoes.

7. Parts of the Continental MarginGranitic • Continental shelf • Gently sloping shallow surface that extends from the shoreline • Contains important resources including: • mineral deposits • oil and natural gas • sand and gravel deposits • fishing areas • Most organisms of the ocean are found in this region because of the amount of sunlight, oxygen, and nutrients

8. Continental slope • Found at the edge of the continental shelf • Much steeper than the shelf • The bottom of the slope is the boundary between the oceanic and continental crust • Submarine canyons are found on the slope. • Submarine canyons are formed by turbidity currents. • A turbidity current is a rapid down slope flow of water. The word turbid means full of sediment. • The current erodes part of the slope forming a canyon. • The water carries a large amount of sediment down the slope.

9. Submarine Canyon & Turbidity Current

11. Continental rise • Only occur in areas where there are no trenches • Found at the base of the continental slope • Consists of sediments from the continental shelf

13. Ocean Basin FloorBasaltic • Located between the continental margin and mid ocean ridge • Consists of abyssal plains, trenches, seamounts, and guyots.

14. Abyssal Plains • Deep, flat regions of the ocean floor where there is no tectonic activity • Covered with a thick layer of sediment • The largest abyssal plains are found in the Atlantic ocean.

16. Deep Ocean Trenches • Deepest parts of the ocean with the highest pressures. • Most are located around the Pacific Ocean • Form at convergent boundaries where subduction occurs • Earthquakes and volcanic activity are associated with this these regions.

18. Seamounts • Individual volcanoes found on the ocean floor that do not reach the ocean surface. • Guyots • A submerged volcanic island that has a flat top due to erosion by water.

20. Mid Ocean Ridges • System of mountains that have developed on the ocean floor • Longest feature on the earth’s surface • The mid ocean ridge is created by a divergent boundary and is broken into segments by transform faults • The volcanic activity along the mid ocean ridge occurs due to seafloor spreading.

21. The type of volcanoes that form along the mid ocean ridges are fissure volcanoes • The long opening at the top of the ridge is called a rift • New ocean floor is formed at the mid ocean ridge and pushes older ocean floor away from the ridge. • Hydrothermal vents are found along mid ocean ridges which contain abundance of minerals.

23. Coral Reefs and Atolls • Fringing reef: form around volcanic islands. • Barrier reef: form farther from an island as a volcano sinks. • Coral atoll: form when an island is completely under water and the reef is all that remains. • The water that the atoll encircles is called a lagoon. • The coral continue to grow upward even though the island is sinking because they can only survive in shallow water.

25. 14.3 Seafloor Sediment • Coarse sediment such as sand covers the continental shelf and slope because it is heavier and settles out first. • Fine sediments such as clay covers the deep ocean floor because it is lighter and settles out last. • Ocean floor sediments can be classified according to their origin: • Terrigenous sediments • Biogenous sediments • Hydrogenous sediments

26. Terrigenous sediment • Any sediment that originated on land • Biogenous Sediment • Any sediment that came from organisms that used to be alive. • 3 types of biogenous sediment: • Calcareous ooze: calcium carbonate shells • Siliceous ooze: shells of single-cell organisms • Phosphate –rich material: bones, teeth, and scales of fish

27. Hydrogenous sediment • Minerals the crystallize directly from ocean water • Manganese and iron form nodules • Calcium carbonates form limestone • Evaporites form salts

28. Seafloor sediments and remains of organisms can provide data about changes in climate over time.

29. 14.4 Resources from the Sea Floor • The ocean floor is rich in mineral and energy resources. • There are many challenges and high costs to retrieving them however. • Most of the value of resources from the ocean comes from their use as energy products. • The resources of the ocean floor are finite and need to be conserved.

30. Oil and natural gas are the main energy products obtained from the ocean floor. • The remains of organisms that lived in the ocean are the source of oil and natural gas. • The percentage of the world’s oil produced from offshore regions has increased to over 30%. • Major offshore reserves exist in the Persian Gulf, the Gulf of Mexico, off the coast of southern California, and the North Sea. • The environmental concern associated with offshore drilling is the possibility of damage to the environment due to oil spills.