2. Focus Question 9.1
How does the area of Earth’s surface covered by oceans compare with the area covered by continents? 2

3. The Vast World Ocean Earth is referred to as the blue planet
71% of Earth’s surface is oceans and marginal seas
Continents and islands comprise the remaining 29%
The Northern Hemisphere is the land hemisphere
The Southern Hemisphere is the water hemisphere

4. The Vast World Ocean

5. The Vast World Ocean Four main ocean basins 1. Pacific Ocean
The largest with the greatest depth
2. Atlantic Ocean
About half the size of Pacific and not as deep
3. Indian Ocean
Slightly smaller than Atlantic, largely in Southern Hemisphere
4. Arctic Ocean
About 7% the size of the Pacific

6. The Vast World Ocean

7. Focus Question 9.1
How does the area of Earth’s surface covered by oceans compare with the area covered by continents?
71% covered by oceans; 29% by land
Most land in northern hemisphere 7

8. Focus Question 9.2
What are the two primary sources for the elements that comprise the dissolved components in seawater? 8

9. Composition of Seawater
Salinity
The total amount of solid material dissolved in water
Typically expressed as a percent
Dissolved substances in seawater are in such small quantities that expressed in parts per thousand
Most of the salt in seawater is sodium chloride

10. Dissolved Components in Seawater

11. Composition of Seawater
Sources of sea salts
Chemical weathering of continental rocks
Earth’s interior through volcanic eruptions
Process called outgassing
Composition of seawater has been relatively stable for millions of years
Material removed as rapidly as added

12. Composition of Seawater
Processes affecting seawater salinity
Changes in water content of the solution
Addition of fresh water
Precipitation
Runoff
Icebergs and sea-ice melting
Removal of fresh water
Evaporation
Formation of sea ice
Latitude and seasons

13. Composition of Seawater

14. Focus Question 9.2
What are the two primary sources for the elements that comprise the dissolved components in seawater?
Chemical weathering of continental rocks
Earth’s interior through volcanic eruptions 14

15. Focus Question 9.3
What two factors influence seawater density? Which one has the greater influence on surface seawater density? 15

16. Variations in Temperature and Density with Depth
Temperature variations
Thermocline
Rapid change of temperature with depth
Thermo = heat
Cline = slope
Creates a vertical barrier in ocean column
Not present at high latitudes (isothermal)

17. Variations in Temperature and Density with Depth

18. Variations in Temperature and Density with Depth
Density variations
Influenced by salinity
Increased salinity = increased density
Influenced by temperature
Increased temperature = decreased density
Greater variations in temperature result in a greater impact of this factor on density
Influenced by depth
Increased depth = increased density
Pycnocline = rapid change of density with depth
Not present at high latitudes (isopycnal)

19. Variations in Temperature and Density with Depth

20. Variations in Temperature and Density with Depth
Layered ocean
Layered according to density
3-layer structure
Shallow surface mixed zone
Transition zone
Deep zone
Does not exist in high latitudes

21. Focus Question 9.3
What two factors influence seawater density? Which one has the greater influence on surface seawater density?
Salinity and temperature
Temperature has the greater influence 21

22. Focus Question 9.4
Describe how satellites orbiting Earth can determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater. 22

23. An Emerging Picture of the Ocean Floor
Bathymetry
Mapping ocean depths and the shape, or topography, of the ocean floor
Echo sounder (sonar)
Invented in the 1920s
Primary instrument for measuring depth
Reflects sound from ocean floor

24. An Emerging Picture of the Ocean Floor

25. An Emerging Picture of the Ocean Floor
Multibeam sonar
Array of sound sources and listening devices
Obtains a profile of a narrow strip of seafloor
Satellite altimeter
Satellites equipped with radar altimeters
Measures variations of the sea surface from space

26. An Emerging Picture of the Ocean Floor

27. An Emerging Picture of the Ocean Floor

28. An Emerging Picture of the Ocean Floor

29. An Emerging Picture of the Ocean Floor
Provinces of the Ocean Floor
Three major topographic units
1. Continental margins
Passive
Active
2. Ocean basin floor
Seamount
Abyssal plain
3. Mid-ocean ridge
Rift valley

30. An Emerging Picture of the Ocean Floor

31. Focus Question 9.4
Describe how satellites orbiting Earth can determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater.
Satellites measure differences across the ocean surface. These differences are due to water displacement caused by variations of the ocean floor. 31

32. Focus Question 9.5
Describe the differences between active and passive continental margins. Where is each type found? 32

33. Continental Margins Passive continental margins
Found along most coastal areas that surround the Atlantic Ocean
Not associated with plate boundaries
Experience little volcanism
Few earthquakes

34. Continental Margins Passive continental margin features
Continental shelf
Flooded extension of the continent
Varies greatly in width
Gently sloping
Contains oil and important mineral deposits
Some areas mantled by extensive glacial deposits
Most consist of thick accumulations of shallow-water sediments

35. Continental Margins Passive continental margin features
Continental slope
Marks the seaward edge of the continental shelf
Relatively steep structure
Boundary between continental crust and oceanic crust

36. Continental Margins Submarine canyons Turbidity currents
Passive continental margin features
Submarine canyons
Deep, steep-sided valleys cut into continental slope
Some are seaward extensions of river valleys
Most appear to have been eroded by turbidity currents
Turbidity currents
Downslope movements of dense, sediment-laden water
Deposits are turbidites

37. Continental Margins

38. Continental Margins Passive continental margin features
Continental rise
Found in regions where trenches are absent
Continental slope merges into a more gradual incline
At base of the continental slope, turbidity currents deposit deep-sea fans

39. Continental Margins

40. Continental Margins Active continental margins
Continental slope descends abruptly into a deep-ocean trench
Located primarily around the Pacific Ocean
Accumulations of deformed sediment and ocean crust form accretionary wedges
Some subduction zones have little or no accumulation of sediments

41. Continental Margins

42. Continental Margins

43. Focus Question 9.5
Describe the differences between active and passive continental margins. Where is each type found?
Passive margins mark the boundary between continental and oceanic crust on a single tectonic plate
Passive margins accumulate sediment
Active margins mark the boundary between tectonic plates
Active margins are found along all subduction zones 43

44. Focus Question 9.6
Explain how deep-ocean trenches are related to plate boundaries. 44

45. Features of Deep-Ocean Basins
Deep-ocean trenches
Long, relatively narrow features
Deepest parts of ocean
Most are located in the Pacific Ocean
Located at subduction zones
Associated with volcanic activity
Volcanic island arcs
Continental volcanic arcs

46. Features of Deep-Ocean Basins
Abyssal plains
Likely the most level places on Earth
Sites of thick accumulations of sediment
Found in all oceans
Seamounts and guyots
Isolated volcanic peaks
Many form near oceanic ridges
May emerge as islands
May sink and form flat-topped seamounts called guyots or tablemounts

47. Features of Deep-Ocean Basins

48. Focus Question 9.6
Explain how deep-ocean trenches are related to plate boundaries.
Deep ocean trenches form at subduction zones, which are a form of convergent plate boundary. 48

49. Focus Question 9.7
Although oceanic ridges can be as tall as some mountains on the continents, list some ways that oceanic ridges are different. 49

50. The Oceanic Ridge Mid-ocean ridge
Interconnected ridge system is the longest topographic feature on Earth’s surface
Over 70,000 km (43,000 mi) in length
23% of Earth’s surface
Winds through all major oceans
Along axis of some segments are deep downfaulted structures called rift valleys

51. The Oceanic Ridge

52. The Oceanic Ridge

53. The Oceanic Ridge Oceanic ridges are characterized by:
An elevated position
Extensive faulting
Numerous volcanic structures that have developed on newly formed crust
Consist of layer upon layer of faulted and uplifted basaltic rocks
Mid-Atlantic ridge has been studied more thoroughly than any other ridge system

54. The Oceanic Ridge Elevated position of ridge
Due to hot (less dense) newly formed crust
Cools, contracts and becomes denser as it moves away from mantle upwelling

55. Focus Question 9.7
Although oceanic ridges can be as tall as some mountains on the continents, list some ways that oceanic ridges are different.
Type of plate boundary
Type of volcanism (and composition of lava)
Type of tectonic stress and resulting features 55

56. Focus Question 9.8
List and describe the three basic types of seafloor sediments. 56

57. Seafloor Sediments Ocean floor is mantled with sediment Sources
Turbidity currents
Sediment slowly settles to bottom from above
Thickness varies
Thickest in trenches: up to 10 km
Pacific Ocean: 600 m or less
Atlantic Ocean: 500 to 1000 m
Mud is most common sediment on deep- ocean floor

58. Seafloor Sediments Types of seafloor sediments Terrigenous sediment
Material weathered from continental rocks
Virtually every part of the ocean receives it
Fine particles remain suspended for a long time
Oxidation often produces red and brown colored sediments

59. Seafloor Sediments Biogenous sediment
Shells and skeletons of marine organisms
Most common are calcareous oozes
Siliceous oozes composed of skeletons of diatoms and radiolarians
Phosphate rich materials derived from bones, teeth, and fish scales

60. Seafloor Sediments

61. Seafloor Sediments Hydrogenous sediment
Minerals that precipitate directly from seawater
Most common types include:
Manganese nodules
Calcium carbonates
Metal sulfides
Evaporites

62. Seafloor Sediments

63. Seafloor Sediments Distribution
Coarse terrigenous deposits dominate continental margin areas
Fine terrigenous material common in deeper areas of the ocean basin
Hydrogenous sediment comprises only a small portion of deposits in the ocean
Few places where very little sediment accumulates (mid-ocean ridges)

64. Seafloor Sediments A Storehouse of Climate Data
Organisms recording climate data become part of the sedimentary record
Records of temperature changes revealed in sediment cores from ocean floor

65. Focus Question 9.8
List and describe the three basic types of seafloor sediments.
1. Terrigenous — weathered from continental rocks
2. Hydrogenous — precipitated directly from seawater
3. Biogenous — produced by marine organisms 65