1. The Ocean Floor Chapter - 9
Earth Science, 6e
The Ocean Floor Chapter - 9

2. A-The vast world ocean (page 260)
Earth is often referred to as the blue planet
71% of Earth’s surface is represented by oceans and marginal seas
Continents and islands comprise the remaining 29
Oceans represent 97% of the Hydrosphere

3. Land Hemisphere & Water Hemisphere
Figure 9.1

4. The vast world ocean Four main ocean basins
Pacific Ocean - the largest and deepest
Atlantic Ocean – about half the size of the Pacific Ocean
Indian Ocean – slightly smaller than the Atlantic
Arctic Ocean – about 7 percent the size of the Pacific

5. The oceans of Earth
Figure 13.2 B

6. Mapping the ocean floor (page 265)
Bathymetry – measurement of ocean depths and the shape or topography of the ocean floor
Echo sounder (also referred to as sonar)
Invented in the 1920s
Primary instrument for measuring depth
Reflects sound from ocean floor

7. Echo sounder and multibeam sonar
Figure 9.11

8. Three major topographic units of the Ocean floor
Continental margins (Active and Passive)
Active margins
Passive margins
Ocean basin floor
3. Mid-ocean ridge

9. Major topographic divisions of the North Atlantic Ocean
Figure 9.14

10. I - Continental margins
Passive continental margins
Found along most coastal areas that surround the Atlantic Ocean
Not associated with plate boundaries
Experience little volcanism and
Few earthquakes
Wider sandy beaches

11. Features of a passive continental margin
Figure 13.9

12. Passive continental margins
Comprises three features:
Continental Shelf
Continental Slope
Continental Rise

13. Passive continental margins
Features comprising a passive continental margin
1. Continental shelf
Flooded extension of the continent
Contains oil and important mineral deposits

14. Passive continental margins
Features comprising a passive continental margin
2. Continental slope
Marks the seaward edge of the continental shelf
Relatively steep structure
Submarine canyons and turbidity currents

15. Turbidity currents
Figure 13.10

16. Continental margins Passive continental margins
Features comprising a passive continental margin
3. Continental rise
Found in regions where trenches are absent
Continental slope merges into a more gradual incline – the continental rise
Thick accumulation of sediment

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

18. An active continental margin
Figure 9.18

19. Active continental margins
Deep-ocean trenches
Long, relatively narrow features
Deepest parts of ocean
Most are located in the Pacific Ocean
Sites where moving lithospheric plates plunge into the mantle
Associated with volcanic activity
Volcanic islands arcs (Japan)
Continental volcanic arcs (Andes, Cascades mts)

20. II - Ocean basin floor Abyssal plains Seamounts and guyots
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

21. Ocean basin floor Seamounts and guyots May emerge as an island
May sink and form flat-topped seamounts called guyots or tablemounts

22. III - Mid-ocean ridge Mid-ocean ridge Characterized by
An elevated position
Extensive faulting
Numerous volcanic structures that have developed on newly formed crust

23. Mid-ocean ridge
Interconnected ridge system is the longest topographic feature on Earth’s surface
Over 70,000 kilometers (43,000 miles) in length
Twenty-three percent of Earth’s surface
Winds through all major oceans
Along the axis of some segments are deep down faulted structures called rift valleys

24. Mid-ocean ridge
Consist of layer upon layer of basaltic rocks that have been faulted and uplifted
Mid-Atlantic Ridge has been studied more thoroughly than any other ridge system

25. Seafloor sediments Ocean floor is mantled with sediment Sources
Turbidity currents
Sediment that slowly settles to the bottom from above
Thickness varies
Thickest in trenches – accumulations may approach 10 kilometers

26. Seafloor sediments Thickness varies
Pacific Ocean – about 600 meters or less
Atlantic Ocean – from 500 to 1000 meters thick
Mud is the most common sediment on the deep-ocean floor

27. Seafloor sediments Types of seafloor sediments 1. Terrigenous sediment
Material weathered from continental rocks
Virtually every part of the ocean receives some
Fine particles remain suspended for a long time
Oxidation often produces red and brown colored sediments

28. Seafloor sediments Types of seafloor sediments 2. Biogenous sediments
Shells and skeletons of marine animals and plants
Most common are calcareous oozes produced from microscopic organisms that inhabit warm surface waters
Siliceous oozes composed of skeletons of diatoms and radiolarians
Phosphate rich materials derived from the bones, teeth, and scales of fish and other marine organisms

29. Seafloor sediments Types of seafloor sediments 3. Hydrogenous sediment
Minerals that crystallize directly from seawater
Most common types include
Manganese nodules
Calcium carbonates
Metal sulfides
Evaporites

30. Distribution of marine sediments
Figure 13.17

31. Seafloor sediments Distribution
Coarse terrigenous deposits dominate continental margin areas
Fine-grained terrigenous material is common in deeper areas of the ocean basin
Hydrogenous sediment comprises only a small portion of deposits in the ocean
There are a few places where very little sediment accumulates (Mid-ocean ridges)

32. Resources from the seafloor
Energy resources
Oil and gas
Gas hydrates
Other resources
Sand and gravel
Evaporative salts
Manganese nodules

33. End of Section 1

34. B - Ocean Chemistry (Page 261)
Salinity is the total amount of material dissolved in water. It is the ration of the mass of dissolved substances to the mass of the water. It is expressed in per cent or part per thousand.

35. Origin of Sea salt Sources of sea salts
Chemical weathering of rocks
Outgassing – gases from volcanic eruptions
Processes affecting seawater salinity
Variations in salinity are a consequence of changes in the water content of the solution

36. Composition of seawater
80% of the ocean depth is salty, cold and dark
Seawater consists of about 33‰ to 38‰
(by weight) dissolved minerals
Salinity is the total amount of solid material dissolved in water
Typically expressed in parts-per-thousand (‰)
Average salinity is 35‰
Major constituent is sodium chloride

37. Relative proportions of water and dissolved components in seawater
Figure 9.3

38. Composition of seawater
Processes affecting seawater salinity
Processes that decrease salinity (add water)
Precipitation
Runoff from land
Icebergs melting
Sea ice melting
Processes that increase salinity (remove water)
Evaporation
Formation of sea ice

39. Ocean temperature
Surface water temperature varies with the amount of solar radiation received
Lower surface temperatures are found in high-latitude regions (Polar regions)
Higher temperatures found in low-latitude regions (Equatorial regions)
Flashback: Latitude and Longitude

40. Ocean temperature Temperature variation with depth
Low-latitudes (Equatorial regions)
High temperature at the surface
Rapid decrease in temperature with depth (thermocline)
High-latitudes (Polar regions)
Cooler surface temperatures
No rapid change in temperature with depth; (thermocline absent)

41. Variations in ocean water temperature with depth
Figure 14.4

42. Ocean density
Density is mass per unit volume - how heavy something is for its size
Determines the water’s vertical position in the ocean
Factors affecting seawater density
Salinity (function of temperature)
Temperature - the greatest influence

43. Variations in the ocean’s surface temperature and salinity with latitude
Figure 14.3

44. Ocean density Ocean Density Variations with depth
Low-latitudes (Equatorial regions)
Low density at the surface
Density increases rapidly with depth (pycnocline) because of colder water
High-latitudes (Polar regions)
High-density (cold) water at the surface
Little change in density with depth (pycnocline absent)

45. Variations in ocean water density with depth
Figure 14.5

46. Ocean density Ocean layering Layered according to density
Three-layered structure
1. Surface mixed zone
Sun-warmed zone
Zone of mixing
Shallow (300 meters)

47. Ocean density Ocean layering Three-layered structure
2. Transition zone
Between surface layer and deep zone
Zone of Thermocline and pycnocline
3. Deep zone
Sunlight never reaches this zone
Temperatures are just a few degrees above freezing
Constant high-density water

48. Layering in the ocean
Figure 14.6

49. PRS Review Test
No talking please.

50. Which one is NOT part of a passive continental margin?
a. Continental shelf b. Continental slope c. Continental rise d. Continental trench

51. Which one is NOT true of deep ocean trenches?
a. They are long and narrow depressions at subduction zones
b. They are sites where plates plunge back into the mantle
c. They are associated with mid ocean ridges
d. They are part of active continental margins

52. Calcareous ooze and siliceous ooze are an example of
Terrigenous sediment
Biogenous sediment
Hydrogenous sediment
Both terrigenous sediment and biogenous sediment

53. The _?_ represents a rapid __?_change with depth
a. thermocline; temperature b. pycnocline; temperature c. halocline; pressure d. thermocline; salinity

54. Deep-ocean circulation is referred to as __
Deep-ocean circulation is referred to as __?_circulation and is driven by __?_differences.
a. Thermocline, temperature
b. Pycnocline, density
c. Thermohaline, density
d. Coriolis, latitude

55. This instrument greatly enhanced our knowledge of the ocean floor.
a. Pulsar b. Echo sounder c. Submarine transit d. Tuzometer

56. The oldest ocean floor rock is about _?_ years of age
a. 2 billion
b. 200 million
c. 4.5 billion
d. 15 billion

57. The eastern coast of the US is a (n)
a. Active continental margin
b. Passive continental margin
c. None of the above

58. Which is the correct ordering of the passive margin's subdivisions?
a. Continental shelf-Continental slope- Continental rise-Abyssal plain
b. Continental shelf-Abyssal Plain- Continental rise-Continental slope
c. Abyssal plain- Continental rise- Continental slope-Continental shelf
d. Continental rise-Continental shelf- Continental slope-Abyssal plain

59. Where would you expect to find the thickest accumulation of seafloor sediment?
a. Answer abyssal plain
b. Continental slope
c. Atop seamounts
d. Deep-ocean trench
e. Mid-ocean ridge

60. Which one is NOT one of the three broad subdivisions of the ocean floor?
a. coastal plain b. oceanic ridge c. deep ocean basin d. continental margin