Chapter 20

1. Chapter 20 The Ocean Basins

2. Ocean Facts • ¾ of the earth’s surface is under salt water. • Oceans contain 97% of all water on earth • Mass of the ocean 1/ 4,000 of the mass of the rest of the earth

3. Divisions of Global Ocean • Pacific—largest and deepest • Includes following seas: Japan, South China, Bering and Coral • Atlantic • Includes Arctic “Ocean”, which is really a sea • Includes following seas: Mediterranean, Caribbean, Baltic • Indian—smallest • Includes Arabian and Red seas

5. Exploring the Ocean • Research ships: obtain data about water temperature, salinity, density, currents, depth, etc. • Submersibles: underwater research vessels, many are robots • Bathysphere—early submersible, spherical, had to be connected to a ship on the surface • Bathyscaph—self propelled

6. Sonar • Sound navigation and ranging • Consists of a transmitter and a receiver • Transmitter sends out sound waves to ocean floor • Sound waves bounce off floor and return to the receiver. • Time for round trip tells how deep it is at that point.

7. 20.2: Features of the Ocean Floor • Ocean floor—bottom of the ocean • Continental margins—shallower portions of the ocean floor that are made up of continental crust • Deep ocean basin—portions of ocean floor made up of oceanic crust.

8. Continental Margin Deep Ocean Basin

9. Continental Margins • Continental Shelf—zone of shallow water where the ocean covers the edge of the continent • About 100 miles long on east coast, 25 on west coast • Average depth is under 200 feet

10. Continental Margins • Continental Slope: a steeper slope at the seaward edge of the continental shelf • Submarine canyons: deep valleys in the continental shelf and slope, may be formed by turbidity currents

11. Continental Margins • Turbidity currents: very dense, carry large amounts of sediment, landslides triggered by earthquakes or gravity. • Continental rise: deposit of sediments at base of continental slope

12. Continental shelf Continental slope Continental rise Continental Margin Deep Ocean Basin

14. Deep Ocean Basins Trenches • Deepest parts of the ocean • Occur when ocean crust is going under (subducting) other crust • Associated with earthquakes and volcanism

15. Deep Ocean Basins Abyssal Plains • Flat areas of ocean floor around 2 miles deep • Flattest parts of the earth—depth may change only 10 feet in 800 miles! • Covered with thick sediment carried by currents from continental margins • Atlantic has larger abyssal plains than Pacific since Pacific has many trenches to trap sediment

16. Deep Ocean Basins Mid-Ocean Ridges • Continuous mountain range that run along ocean floor • Have a valley called a rift down middle • Source of seafloor spreading • Most prominent features on ocean floors

18. Deep Ocean Basins • Seamounts—isolated volcanic mountains spread over the ocean floor, common in Pacific • Form islands like Hawaii and Tahiti • If they form islands, the tops tend to get flattened by waves, if sea level drops, they get submerged • Guyots—flat-topped, submerged seamounts

19. 20.3: Ocean Floor Sediments • Sediment size: Sediment near shore is made up of larger particles/fragments, sediment in the middle of the ocean floor is much finer

20. Sources of Sediment • Inorganic—mostly rock particles eroded from continents, could be carried by rivers, wind or glaciers/icebergs • Organic—remains of marine organisms, could be silica (from algae called diatoms) or calcium carbonate (from coral, clams)

21. Sources of Sediment • Chemical Deposits—form when chemicals dissolved in seawater interact and “un-dissolve” (precipitate) and sink to the bottom • Nodules—potato shaped lumps of minerals on ocean floor, could be an important source of minerals—especially manganese

22. Physical Classification of Sediments • Mud—silt and clay sized particles • Ooze—must be at least 30% organic material along with silt/clay, covers 40% of ocean floor • Calcareous ooze—mostly calcium carbonate • Siliceous ooze—mostly silica