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Chapter 24: The Oceans, Atmosphere, and Climatic Effects

Chapter 24 Lecture

This lecture will help you understand:

Earth's Atmosphere and Oceans

Components of Earth's Oceans

Ocean Waves, Tides, and Shorelines

Components of Earth's Atmosphere

Solar Energy

Driving Forces of Air Motion

Global Circulation Patterns

Earth's Atmosphere and Oceans

Seventy-one percent of Earth's surface is covered by water.

Water's high specific heat capacity accounts for moderate temperatures in coastal lands.

Earth's Atmosphere and Oceans

Earth's early atmosphere appeared before the Sun was fully formed.

Hydrogen

Helium

The Sun's formation swept away Earth's original atmosphere and a new atmosphere formed.

Earth's Atmosphere and Oceans

Earth's atmosphere developed in stages:

Hot gases escaped through volcanoes and fissures.

Free oxygen occurred as a result of photosynthesis by cyanobacteria.

Ozone began to accumulate in the upper atmosphere.

Water vapor condensed to form oceans.

Components of Earth's Oceans: The Ocean Floor

The ocean floor encompasses continental margins and deep ocean basins.

Components of Earth's Oceans: The Ocean Floor

Continental margins are between shorelines and deep ocean basins.

Continental shelf—shallow, underwater extension of the continent.

Continental slope—marks boundary between continental and oceanic crust.

Continental rise—wedge of accumulated sediment at base of continental slope.

Components of Earth's Oceans: The Ocean Floor

The ocean bottom is etched with deep canyons, trenches, and crevasses.

Underwater mountains rise upward from the seafloor.

The deep-ocean basin:

Basalt from seafloor spreading plus thick accumulations of sediment

Abyssal plains, ocean trenches, and seamounts

Components of Earth's Oceans: The Ocean Floor

The deep-ocean basin:

Abyssal plains—flattest part of the ocean floor due to accumulated sediment

Ocean trenches—long, deep, steep troughs at subduction zones

Seamounts—elevated seafloor from volcanism

Mid-ocean ridges:

Sites of seafloor spreading (volcanic and tectonic activity)

A global mid-ocean ridge system winds all around the Earth

Components of Earth's Oceans: The Ocean Floor

The deepest parts of the ocean are at the ocean trenches near some of the continents.

The shallowest waters are in the middle of the oceans around underwater mountains (mid-ocean ridge system).

Ocean trenches are the deepest parts of the ocean floor because

that is where oceanic crust meets continental crust.

that is where subduction occurs.

no sediment accumulates in trenches.

all accumulated sediment settles in the abyssal plain.

Components of Earth's Oceans CHECK YOUR NEIGHBOR

B. that is where subduction occurs.

Ocean trenches are the deepest parts of the ocean floor because

that is where oceanic crust meets continental crust.

that is where subduction occurs.

no sediment accumulates in trenches.

all accumulated sediment settles in the abyssal plain.

Components of Earth's Oceans CHECK YOUR ANSWER

B. that is where subduction occurs.

Oceanic crust does meet continental crust at deep ocean trenches, but these plate boundaries do not all have deep trenches.

C. and D. sediment does accumulate in the trenches.

Ocean Waves, Tides, and Shorelines

Characteristics of waves—waves get their energy from the wind.

The crest is the peak of the wave.

The trough is the low area between waves.

Wave height is the distance between a trough and a crest.

Wavelength is the horizontal distance between crests.

Wave period is the time interval between the passage of two successive crests.

Ocean Waves, Tides, and Shorelines

Height, length, and period of a wave depend on:

Wind speed

Length of time wind has blown

Fetch—the distance that the wind has traveled across open water

Ocean Waves, Tides, and Shorelines

Waves on the ocean surface are orbital waves.

Wave energy moves forward: the disturbance moves, not the water.

Occurs in the open sea in deep water.

Ocean Waves, Tides, and Shorelines

Waves at the shoreline:

In shallow water, at a depth of about one-half the wavelength, the wave begins to "feel bottom"

The wave grows higher as it slows and wavelength shortens

As a steep wave front collapses, the wave breaks

The turbulent water created by the crash is called surf

When a wave approaches the shore, the water depth decreases. This affects the wave by flattening its circular motion,

decreasing its speed, and increasing distance between waves and wave height.

increasing its speed and distance between waves, and decreasing wave period.

decreasing its speed and distance between waves, causing wave height to increase.

increasing its speed and distance between waves, causing wave height to increase.

Ocean Waves, Tides, and Shorelines CHECK YOUR NEIGHBOR

C. decreasing its speed and distance between waves, causing wave height to increase.

When a wave approaches the shore, the water depth decreases. This affects the wave by flattening its circular motion,

decreasing its speed, and increasing distance between waves and wave height.

increasing its speed and distance between waves, and decreasing wave period.

decreasing its speed and distance between waves, causing wave height to increase.

increasing its speed and distance between waves, causing wave height to increase.

Ocean Waves, Tides, and Shorelines CHECK YOUR ANSWER

C. decreasing its speed and distance between waves, causing wave height to increase.

Ocean Waves, Tides, and Shorelines: Wave Refraction

As waves enter shallow water:

Forward direction changes.

Wave nearest to shore slows and lags behind incoming waves.

The incoming waves also slow and begin to pivot.

As this continues the wave crest bends and pivots around the slower portion of the wave—wave refraction.

Ocean Waves, Tides, and Shorelines: Wave Refraction

Longshore Current:

The oblique approach of waves—flow is parallel to the shore.

Ocean Waves, Tides, and Shorelines: Wave Refraction

Impact of wave refraction on shorelines:

Wave energy unevenly distributed

Concentrated in headland areas—area of erosion

Diluted in adjacent coves and bays—area of deposition

Ocean Waves, Tides, and Shorelines: The Work of Ocean Waves

Characteristic coastal erosional landforms:

Wave cut platform

Sea cliff

Sea cave

Sea arch

Sea stack

Ocean Waves, Tides, and Shorelines: The Work of Ocean Waves

Characteristic coastal depositional landforms:

Beach

Spit

Lagoon

Barrier island

Inlet

Ocean Waves, Tides, and Shorelines

Coral reefs are composed of actively growing coral organisms.

Organisms secrete calcium carbonate as they grow—that is what we see.

Many reefs survive on photosynthetic algae.

Coral bleaching is an indicator of global warming.

Ocean Waves, Tides, and Shorelines: Link to Physics: Ocean Tides

Tides occur because of the differences in the gravitational pull exerted by the Moon on opposite sides of Earth.

Ocean Waves, Tides, and Shorelines: Link to Physics: Ocean Tides

Because Earth spins on its axis once a day, it should have two distinct tides 12 hours apart.

But because the Moon moves around Earth, the times of the tides vary each day.

Ocean Waves, Tides, and Shorelines: Link to Physics: Ocean Tides

Alignment of the Sun, Earth, and Moon causes spring tides—more dramatic highs and lows.

Ocean Waves, Tides, and Shorelines: Link to Physics: Ocean Tides

When the pull of the Sun and Moon are perpendicular to each other, we get neap tides—the highs not as high, and the lows not as low.

Components of Earth's Atmosphere

Earth's atmosphere is divided into layers, each with different characteristics:

Troposphere

Stratosphere

Mesosphere

Thermosphere

Ionosphere

Exosphere

Components of Earth's Atmosphere

Troposphere:

Lowest and thinnest layer

16 km at equator, 8 km at poles

90% of the atmosphere's mass

Where weather occurs

Water vapor and clouds

Temperature decreases with altitude

6ºC per kilometer

Top of troposphere averages –50ºC

Components of Earth's Atmosphere

Stratosphere:

Top of troposphere to 50 km above surface

Ozone layer

Absorbs harmful UV radiation

Temperature increases because of ozone absorption of UV radiation.

Ranges from –50ºC at base to 0ºC at top

Components of Earth's Atmosphere

Mesosphere:

Extends from stratosphere to altitude of 80 km

Temperature decreases with altitude

Gases in this layer absorb very little UV radiation.

0ºC at bottom to –90ºC at top

Components of Earth's Atmosphere

Thermosphere:

Temperature increases with altitude

Temperature is related to average speed of gas molecules—very high speed gives high temperatures

Temperatures up to 1500ºC

Very low density of gas molecules means very little heat absorption—it would feel cold.

Components of Earth's Atmosphere

Ionosphere:

Electrified region within the thermosphere and upper mesosphere

Auroras: fiery displays of light near Earth's magnetic poles

Exosphere:

The interface between Earth and space

Beyond 500 km, atoms and molecules can escape to space

Components of Earth's Atmosphere

The average temperature of Earth's atmosphere varies in a zig-zag pattern with altitude.

Solar Energy

Solar radiation is electromagnetic energy emitted by the Sun.

Visible, short-wavelength radiation

Terrestrial radiation is reemitted solar radiation from Earth's surface.

Infrared, longer-wavelength radiation

Solar Energy

The Sun warms Earth's ground, and the ground, in turn, warms Earth's atmosphere.

Earth's temperature varies according to the degree of solar intensity—the amount of solar radiation per area.

Where solar intensity is higher, temperatures are higher.

Solar Energy

Solar intensity is highest where the Sun's rays strike Earth's surface straight on.

Flashlight beam at 90º angle to the surface

Equatorial regions

Solar intensity is weaker where the Sun's rays strike Earth's surface at an angle.

Flashlight beam at an angle

Higher latitudes

Solar Energy

Variation in solar intensity with latitude and the tilt of the Earth's axis helps to explain the different seasons.

Solar Energy

When the Sun's rays are closest to perpendicular at any spot on the Earth, that region's season is summer.

Six months later, as the rays fall upon the same region more obliquely, the season is winter.

In between are the seasons fall and spring.

Solar Energy: The Greenhouse Effect and Global Warming

Human activities pump greenhouse gases into the atmosphere: carbon dioxide, methane, nitrous oxide, ozone, CFCs.

The result is a warming Earth.

Driving Forces of Air Motion

Underlying Driving Force:

Unequal heating of Earth's surface

Atmospheric pressure:

Force the atmosphere exerts on a surface area

At any level in the atmosphere, force = total weight of air above that level.

At higher elevations, with fewer air molecules above the atmospheric pressure is less.

Convection Cycle:

Warm air parcel rises; Cooler air parcel sinks

Warm air is less dense than cool air

Convection currents stir the wind:

Wind is air that flows horizontally from higher pressure to lower pressure.

The greater the pressure gradient, the stronger the wind.

Driving Forces of Air Motion: Temperature-Pressure Relationship

Pressure differences are caused by uneven heating of the Earth's surface.

Local differences in heating contribute to small-scale local winds.

Planet-scale differences occur because of solar intensity variations—equatorial regions have greater solar intensity than polar regions.

Differences contribute to global wind patterns, the prevailing winds.

Atmospheric pressure is greatest near the Earth's surface because

of the weight of all the air above.

90% of Earth's atmosphere is in the troposphere.

of warmer temperatures.

of water vapor.

Driving Forces of Air Motion CHECK YOUR NEIGHBOR

A) of the weight of all the air above.

Atmospheric pressure is greatest near the Earth's surface because

of the weight of all the air above.

90% of Earth's atmosphere is in the troposphere.

of warmer temperatures.

of water vapor.

Driving Forces of Air Motion CHECK YOUR ANSWER

A) of the weight of all the air above.

What drives air from areas of high pressure to areas of low pressure?

Convection currents.

Wind.

The pressure-gradient force.

Water vapor.

Driving Forces of Air Motion CHECK YOUR NEIGHBOR

C. The pressure-gradient force.

What drives air from areas of high pressure to areas of low pressure?

Convection currents.

Wind.

The pressure-gradient force.

Water vapor.

Driving Forces of Air Motion CHECK YOUR ANSWER

C. The pressure-gradient force.

Driving Forces of Air Motion: Temperature-Pressure Relationship

Warm air characteristics:

Warm air expands

Warm air has lower density and lower pressure

Cool air characteristics:

Cool air contracts

Cool air has higher density and higher pressure

Driving Forces of Air Motion: Temperature-Pressure Relationship

Local winds:

Not all surfaces are heated equally.

Example: Land heats and cools more rapidly than water.

Unequal heating results in pressure differences. And pressure differences result in wind.

Remember: Wind is air that flows horizontally from higher pressure to lower pressure.

More energy is required to raise the temperature of water than that of land. Once heated, water will retain the heat longer than land. This concept is related to

expansion of warm air.

pressure differences of land and water.

Water's high specific heat capacity.

expansion of seawater.

Driving Forces of Air Motion CHECK YOUR NEIGHBOR

C. Water's high specific heat capacity.

Driving Forces of Air Motion CHECK YOUR ANSWER

More energy is required to raise the temperature of water than that of land. Once heated, water will retain the heat longer than land. This concept is related to

expansion of warm air.

pressure differences of land and water.

Water's high specific heat capacity.

expansion of seawater.

C. Water's high specific heat capacity.

At a hypothetical school yard there is a blacktop area and a grassy area. On a particularly warm day, a small breeze develops. Air moves from

the grassy area to the blacktop.

the blacktop to the grassy area.

low pressure to high pressure.

Not enough information.

Driving Forces of Air Motion CHECK YOUR NEIGHBOR

A. the grassy area to the blacktop.

Driving Forces of Air Motion CHECK YOUR ANSWER

At a hypothetical school yard there is a blacktop area and a grassy area. On a particularly warm day, a small breeze develops. Air moves from

the grassy area to the blacktop.

the blacktop to the grassy area.

low pressure to high pressure.

Not enough information.

Explanation:

Air above the blacktop is hotter (low pressure) than air above the grassy area (higher pressure). Air moves from high to low, so breeze will blow from grassy area to blacktop.

A. the grassy area to the blacktop.

Driving Forces of Air Motion

Earth's rotation greatly affects the path of moving air.

Coriolis force: Moving bodies (such as air) deflect to the right in the Northern Hemisphere, to the left in the Southern Hemisphere.

Deflection of wind varies according to speed and latitude.

Faster wind, greater deflection

Deflection greatest at poles, decreases to zero at equator

Driving Forces of Air Motion

Factors that affect wind:

The pressure gradient force: air moves from high pressure to low pressure

The Coriolis force: apparent deflection of winds due to Earth's rotation

Frictional force: air moving close to ground encounters friction

Driving Forces of Air Motion

Global Circulation Patterns

Global circulation of the atmosphere results from unequal heating of Earth's surface and Earth's rotation.

Global Circulation Patterns

At the equator:

Rising warm, moist air creates a zone of low surface pressure: Doldrums

Trade winds (0º–30º)

At 30º N and S latitude:

Air cools and sinks to create dry air and high pressure: Horse latitudes

Deserts

Westerlies (30º–60º)

At 60º N and S latitude:

Cool, dry air meets warm, moist air to create a zone of low pressure: Polar Front

Polar easterlies (60º–90º)

The prevailing westerly winds are affected by the Coriolis effect by the deflection of winds

to the right in the Northern Hemisphere and left in the Southern Hemisphere.

to the left in the Northern Hemisphere and right in the Southern Hemisphere.

laterally toward the poles.

westward.

Global Circulation Patterns CHECK YOUR NEIGHBOR

A. to the right in the Northern Hemisphere and left in the Southern Hemisphere.

Global Circulation Patterns CHECK YOUR ANSWER

The prevailing westerly winds are affected by the Coriolis effect by the deflection of winds

to the right in the Northern Hemisphere and left in the Southern Hemisphere.

to the left in the Northern Hemisphere and right in the Southern Hemisphere.

laterally toward the poles.

westward.

Explanation:

Winds are named for the direction from which they blow. Westerlies blow from the west to the east.

A. to the right in the Northern Hemisphere and left in the Southern Hemisphere.

The prevailing winds in North America are westerly—they blow from west to east. Westerly winds contribute to cooling the western coast

in the winter and warming it in the summer.

in the summer and warming it in the winter.

so that the temperature is the same all year long.

and making temperature variations more extreme.

Global Circulation Patterns CHECK YOUR NEIGHBOR

B. in the summer and warming it in the winter.

Global Circulation Patterns CHECK YOUR ANSWER

The prevailing winds in North America are westerly—they blow from west to east. Westerly winds contribute to cooling the western coast

in the winter and warming it in the summer.

in the summer and warming it in the winter.

so that the temperature is the same all year long.

and making temperature variations more extreme.

B. in the summer and warming it in the winter.

Global Circulation Patterns: Oceanic Circulation

Ocean currents are streams of water that move, relative to the larger ocean.

Like the atmosphere, oceans have several vertical layers: surface zone, transition zone, and deep zone.

Global Circulation Patterns: Surface Currents

Surface currents are created by wind.

Surface ocean currents correspond to the direction of the prevailing winds.

Global Circulation Patterns: Surface Currents

Ekman transport: Coriolis force causes water currents to deflect up to 45º.

Global Circulation Patterns: Surface Currents

Factors that influence ocean currents:

For short distances, wind is strongest factor

For longer distances, Coriolis force comes into play:

Coriolis causes surface currents to turn and twist into semicircular whirls called gyres.

Northern Hemisphere gyres rotate clockwise.

Southern Hemisphere gyres rotate counterclockwise.

Global Circulation Patterns: Surface Currents

Gyres cause heat transport from equatorial regions to higher latitudes.

The Gulf Stream current carries vast quantities of warm tropical water to higher latitudes.

Global Circulation Patterns: The El Niño Condition

Years in which the Trade winds fail to strengthen are called El Niño years.

El Niño Southern Oscillation influences climate on both sides of the Pacific Ocean.

Global Circulation Patterns: Deep Water Currents

Deeper waters are driven not by winds but by gravity.

Polar water freezes, increasing the salinity of the liquid water. Cold, salty water continuously sinks to the ocean bottom.

The sinking water pushes deeper water out of the way, causing the bottom water to flow outward along the ocean floor.

A combination of deep-water mixing by ocean-floor tidal stirring and upwelling due to favorable winds brings the deep waters slowly back to the surface.

This conveyor-belt process may take thousands of years.