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The Ocean Floor Chapter - 9

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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

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