Earth Science, 6e The Ocean Floor Chapter - 9. A-The vast world ocean (page 260) Earth is often referred to as the blue planet 71% of Earths surface is.

Earth Science, 6e

The Ocean FloorChapter - 9

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

Land Hemisphere

&Water

HemisphereFigure 9.1

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

The oceans of Earth

Figure 13.2 B

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

Echo sounder and multibeam sonar

Figure 9.11

Three major topographic units of the Ocean floor

1. Continental margins (Active and Passive)• Active margins

• Passive margins

2. Ocean basin floor

3. Mid-ocean ridge

Major topographic divisions of the North Atlantic Ocean

Figure 9.14

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

Features of a passive continental margin

Figure 13.9

Passive continental margins

• Comprises three features:

– Continental Shelf– Continental Slope– Continental Rise

Passive continental margins

• Features comprising a passive continental margin

1. Continental shelf

• Flooded extension of the continent

• Contains oil and important mineral deposits

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

Turbidity currents

Figure 13.10

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

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)

An active continental margin

Figure 9.18

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)

II - Ocean basin floor

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

Ocean basin floor

Seamounts and guyots• May emerge as an island • May sink and form flat-topped seamounts

called guyots or tablemounts

III - Mid-ocean ridge

• Mid-ocean ridge

• Characterized by

• An elevated position

• Extensive faulting

• Numerous volcanic structures that have developed on newly formed crust

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

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

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

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

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

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

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

Distribution of marine sediments

Figure 13.17

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)

Resources from the seafloor

Energy resources • Oil and gas• Gas hydrates

Other resources • Sand and gravel • Evaporative salts • Manganese nodules

End of Section 1

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.

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

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

Relative proportions of water and dissolved

components in seawater

Figure 9.3

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

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

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)

Variations in ocean water temperature with depth

Figure 14.4

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

Variations in the ocean’s surface temperature and

salinity with latitude

Figure 14.3

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)

Variations in ocean water density with depth

Figure 14.5

Ocean density

Ocean layering • Layered according to density • Three-layered structure

1. Surface mixed zone

• Sun-warmed zone

• Zone of mixing

• Shallow (300 meters)

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

Layering in the ocean

Figure 14.6

PRS Review Test

No talking please.

Which one is NOT part of a passive continental margin?

a. Continental shelf

b. Continental slope

c. Continental rise

d. Continental trench

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

Calcareous ooze and siliceous ooze are an example of

a. Terrigenous sediment

b. Biogenous sediment

c. Hydrogenous sediment

d. Both terrigenous sediment and biogenous sediment

The _?_ represents a rapid __?_change with depth

a. thermocline; temperature

b. pycnocline; temperature

c. halocline; pressure

d. thermocline; salinity

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

This instrument greatly enhanced our knowledge of the ocean floor.

a. Pulsar

b. Echo sounder

c. Submarine transit

d. Tuzometer

The oldest ocean floor rock is about _?_ years of age

a. 2 billion

b. 200 million

c. 4.5 billion

d. 15 billion

The eastern coast of the US is a (n)

a. Active continental margin

b. Passive continental margin

c. None of the above

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

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

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