The Ocean Floor

1. The Ocean Floor

2. The Ocean Floor • The World Ocean • Imaging the Ocean Floor • Continental Margins • The Deep-Ocean Floor • Oceanic Ridges • Seafloor Sediments

3. Terms

4. Oceanography: An Interdisciplinary Science PSCI 131: The Ocean Floor • Geology • Ocean floor, oceanic crust • Biology • Marine life • Chemistry • Composition of ocean water • Physics • Waves, heat transfer, ocean circulation

5. The World Ocean PSCI 131: The Ocean Floor

6. The World Ocean PSCI 131: The Ocean Floor Earth’s surface is 71% ocean Majority is in Southern Hemisphere Northern Hemisphere Southern Hemisphere

7. PSCI 131: The Ocean Floor: The World Ocean

8. Oceans vs. Continents PSCI 131: The Ocean Floor: The World Ocean • Continents • Average elev.: about 2800 feet above sea level • Highest point: about 30,000 feet a.s.l. • Oceans • Average depth: about 12,200 feet • Deepest point: about 36,000 feet

9. Imaging the Ocean Floor PSCI 131: The Ocean Floor

10. Ocean Floor Mapping PSCI 131: The Ocean Floor: Imaging the Ocean Floor • HMS Challenger • British • 1872-1876 • All oceans except Arctic • Used weighted ropes to find ocean depths

11. Ocean Floor Mapping PSCI 131: The Ocean Floor: Imaging the Ocean Floor • HMS Challenger’s route • British • 1872-1876 • All oceans except Arctic • Used weighted ropes to find ocean depths

12. Ocean Floor Mapping PSCI 131: The Ocean Floor: Imaging the Ocean Floor • Sonar • Single beam • Multibeam

13. Ocean Floor Mapping PSCI 131: The Ocean Floor: Imaging the Ocean Floor • Sonar • Travel time of ping / 2 = depth

14. Seismic Reflection Profiles PSCI 131: The Ocean Floor: Imaging the Ocean Floor • Seismic waves penetrate mud, bounce off rock

15. Seismic Reflection Profiles PSCI 131: The Ocean Floor: Imaging the Ocean Floor

16. Ocean Floor Provinces PSCI 131: The Ocean Floor: Imaging the Ocean Floor • Revealed by ocean floor imaging techniques • Continental margins • Passive and active • Deep-ocean floor • Oceanic ridges

17. Ocean Floor Provinces PSCI 131: The Ocean Floor: Imaging the Ocean Floor

18. Continental Margins PSCI 131: The Ocean Floor

19. Continental Margin Types PSCI 131: The Ocean Floor: Continental Margins • Passive • Little geologic activity • Gentle slope • Flatter coastlines • Active • Frequent geologic activity • Steeper slope • More rugged coastlines

20. Passive Margins PSCI 131: The Ocean Floor: Continental Margins

21. Passive Margins PSCI 131: The Ocean Floor: Continental Margins

22. Passive Margin Formation PSCI 131: The Ocean Floor: Continental Margins Crustal stretching & thinning Initial, narrow ocean basin forms Mature basin with passive margins

23. Passive Margins: Submarine Canyons PSCI 131: The Ocean Floor: Continental Margins Undersea “landslides” move down continental slopes and cut into shelves to form submarine canyons.

24. Passive Margins: The Hudson submarine canyon PSCI 131: The Ocean Floor: Continental Margins Modern Hudson River mouth Hudson River mouth during last ice age

25. PSCI 131: The Ocean Floor: Continental Margins Active Margins (aka subduction zones)

26. PSCI 131: The Ocean Floor: Continental Margins Active Margins (aka subduction zones)

27. The Deep-Ocean Basin PSCI 131: The Ocean Floor

28. Key Deep-Ocean Basin Features PSCI 131: The Ocean Floor: The Deep-Ocean Basin • Abyssal plains • Trenches • Seamounts

29. Abyssal Plains PSCI 131: The Ocean Floor: The Deep-Ocean Basin • Very flat • Deep sediment

30. Abyssal Plains PSCI 131: The Ocean Floor: The Deep-Ocean Basin Abyssal plains are dark blue

31. Trenches PSCI 131: The Ocean Floor: The Deep-Ocean Basin • Deepest places in the oceans • Subduction-related • Sediment traps Florida Puerto Rico Trench

32. Seamounts PSCI 131: The Ocean Floor: The Deep-Ocean Basin • Undersea volcanoes • Form islands if peaks are above sea level • Most are not

33. Oceanic Ridges PSCI 131: The Ocean Floor

34. Oceanic Ridges PSCI 131: The Ocean Floor: Oceanic Ridges • Elevated, linear features

35. Oceanic Ridges PSCI 131: The Ocean Floor: Oceanic Ridges • Also called “spreading centers” or “divergent plate boundaries” • Two crustal plates are spreading apart • New crust formed at center of ridge

36. Diagram of an oceanic ridge PSCI 131: The Ocean Floor: Oceanic Ridges Central rift valley w/ volcanoes Plate motion Plate motion Fault blocks Rising molten rock from mantle

37. Oceanic ridge formation PSCI 131: The Ocean Floor: Oceanic Ridges

38. Earth’s Largest Topographic Feature PSCI 131: The Ocean Floor: Oceanic Ridges • Over 70,000 miles long

39. Seafloor Sediments PSCI 131: The Ocean Floor

40. Ocean Sediment Types PSCI 131: The Ocean Floor: Seafloor Sediments • Terrigenous (~45% of ocean floor) • “Terra” = earth • Derived from continents • Biogenous (~55%) • Created by organisms • Hydrogenous (<1 %) • Crystallize out of seawater

41. Terrigenous Sediments PSCI 131: The Ocean Floor: Seafloor Sediments • Concentrated along continental margins • Mineral and rock material • From rivers, wind, glaciers

42. Biogenous Sediments PSCI 131: The Ocean Floor: Seafloor Sediments • Concentrated away from continents • Mainly dead plankton shells White Cliffs of Dover, England – ancient biogenous seafloor sediment Plankton shells at high magnification

43. Hydrogenous Sediments PSCI 131: The Ocean Floor: Seafloor Sediments • Dispersed throughout ocean and along shorelines • Chemical precipitation of minerals from seawater • Common examples • Manganese nodules • Calcium carbonate Manganese nodules in south Pacific, depth 15,000 feet

44. End of Chapter PSCI 131: The Ocean Floor