CHAPTER 13

OCEANS, WINDS,

WAVES, AND COASTLINES

 

The Atmosphere

 

The gaseous envelope that surrounds a planet or any other celestial body. 

 

Air is the gaseous envelope that surrounds one particular planet. 

 

Air is the earth’s atmosphere.

 

Air Composition

 

Invisible, odorless mixture of gases and suspended particles.

 

The composition of air varies slightly from place to place and time to time in the same place because of the presence of aerosols and water vapor.

 

Aerosols

 

Liquid droplets or solid particles that are very small and as a result remain suspended in the air. 

 

Water droplets in fogs are liquid aerosols.

 

Tiny ice crystals, smoke particles from fires, sea-salt crystals from ocean spray are solid aerosols.

 

Water Vapor

 

Always present in the air

 

Amount is termed the humidity

 

Dry Air Composition

 

Composition of air without water vapor and aerosols:

 

1.     Nitrogen – 78.08%

2.     Oxygen – 21%

3.     Argon – 0.93%

 

 

 

 

Layers In the Atmosphere

 

1.     Troposphere - bottom layer

2.     Stratosphere

3.     Mesosphere

4.     Thermosphere

 

Troposphere

 

Humans live at the bottom of the troposphere

 

Contains 80% of the actual mass of the atmosphere, including nearly all the water vapor and clouds

 

Weather related phenomena originate here

 

Constantly moving and thoroughly mixed by winds

 

Contains most of the heat-absorbing gases (greenhouse gases) that warm the earth’s surface

 

Greenhouse effect – the process through which long-wavelength (infrared) heat energy is absorbed by gases in the atmosphere, thereby warming the surface of the earth. 

 

Without the greenhouse effect, the surface of the earth would be a cold and inhospitable place.

 

Stratosphere and the
 Ozone Layer

 

15km – 50km

 

Contains 19% of the atmosphere’s total mass

 

Long u.v. wavelengths are absorbed

 

Ozone (O₃) is present in tiny but vital amounts and absorbs the most dangerous of the uv rays. 

 

This layer in the stratosphere is called the ozone layer.

 

If we breakdown the ozone in the stratosphere, the amount of long-wavelength uv radiation reaching the earth’s surface may increase.

 

 

Mesosphere

 

50km – 80km

 

Intermediate uv wavelengths are absorbed

 

Thermosphere

 

80km – 160km

 

Short uv wavelengths are absorbed

 

Oceans

 

The atmosphere and oceans are closely interconnected. 

 

Water and CO₂ are exchanged freely between them via evaporation and precipitation. 

 

The oceans help regulate the temps and humidity of the lower part of the atmosphere.

 

Ocean Basins

 

Oldest rocks discovered on earth (about 4.0 b.y. ago) are gneisses that were once sedimentary strata deposited in water. 

 

We therefore know that the earth had liquid water on its surface 4 b.y. ago.

 

The water in the oceans likely came from steam produced during primordial volcanic eruptions.

 

The world’s oceans cover 71% of the earth’s surface.

 

Seawater Composition

 

Salinity – The saltiness of seawater expressed in ppt.

 

            The salinity of seawater ranges between 33 and 37 ppt.

 

Na⁺ and Cl^- are the main ions present in seawater.

 

 

 

 

The dissolved elements in seawater come from two main sources:

 

1.     weathering

2.     volcanic eruptions

 

Chemical Weathering

 

Chemical weathering releases soluble materials such as salts of Na, K, and S into the waters.

 

Volcanic Eruptions

 

Volcanic eruptions emit volcanic gases and hot springs which contribute soluble compounds into waters.

 

Seawater Composition

 

The salinity of seawater varies within narrow limits and is balanced by the interplay of several processes:

 

1.     Evaporation

2.     Precipitation

3.     Inflow of Fresh Water from Rivers

4.     Freezing of Sea Ice

 

Processes Affecting
 Seawater Salinity

 

1.     Evaporation– that removes water, so the remaining water is saltier. 

            Important in desert regions

 

2.     Precipitation – Rainfall and snowfall add fresh water and the make the sea less salty. 

           

                        This effect is more pronounced in areas of high rainfall near                           the equator

 

3.     Inflow of fresh water from rivers – Makes the sea less salty.

 

4.     Freezing of sea ice – Salts are excluded from the ice, leaving the unfrozen seawater saltier. 

                       

                        This effect is pronounced at the polar regions.

 

 

 

Oceans

 

The quantity of dissolved matter that has been added to the sea over billions of year far exceeds the amount now dissolved in the ocean.

 

The reason the sea isn’t saltier than it is, is because chemical substances are being removed from seawater at the same rate that they are being added.

 

The composition of seawater has remained essentially unchanged.

 

Surface ocean currents, slow drifts of water, are set in motion by the prevailing winds.

 

The ultimate energy source for the motion of the surface ocean currents is not the wind but the sun.

 

Solar energy sets into motion the planetary wind system. 

 

The ocean circulation results from the interplay of several key elements in the earth system:

 

1.     Radiation from the sun, which provides heat energy to the atmosphere

 

2.     Non-uniform heating, which generates winds

 

3.     The winds, which in turn, drive the movement of water in the surface layer of the ocean

 

Tides and Sea Level Changes

 

Tides – The cycles of regular rise and fall in the level of water in the ocean and other large bodies of water, that result from the gravitational interaction of the Moon, Sun, and the Earth.

 

Gravitational attraction causes ocean water to bulge upward on the side of the earth nearest to the moon.

 

On the opposite side of the earth, inertia (the force that tends to maintain a body in uniform linear motion) created by the earth’s motion around the common center of mass of the earth-moon system also causes ocean water to bulge, but in the opposite direction.

 

 

Due to the great distance of the sun from earth, the sun’s gravitational force is only half as effective as the moon in producing tides.

 

Wave Action Along Shorelines

 

Surf – The broken, turbulent water found between a line of breakers and the shore, forming an area known as the surf zone. 

 

Surf is a powerful erosional force.

 

Longshore current – A current, within the surf zone, that flows parallel to the coast. 

           

            Sediment brought to the sea by rivers is redistributed by the             longshore current.

 

Beach Drift – The movement of particles along a beach as they are driven up and down the beach slope by wave action.

 

Shorelines and Coastal Landforms

 

The constant interplay between erosional and depositional forces along coastlines produces a variety of shorelines and coastal landforms. 

 

Three basic types of Shoreline and Coastal Landforms

 

1.     Rocky (cliffed) Coast

 

                        Most common type of coast (80%)

 

                        Characterized by wave-cut cliffs – a coastal cliff cut by wave                                     action at the base of a rocky coast.

 

2.     Lowland Beach

 

                        Beach is defined as a wave-washed sediment along a coast. 

 

3.     Barrier Island Coast

 

 

 

 

 

 

 

 

Common depositional landforms associated with beaches include:

 

Barrier Island - a long, narrow, sandy island lying offshore and parallel to a lowland coast.

 

Spit – An elongated ridge of sand or gravel that project from land and ends in open water.

 

Tombolo – a spitlike ridge of sand or gravel that connects an island to the mainland.

 

Coral Reef

 

            Reef – A structure composed mainly of the calcareous remains of   marine organisms (principally corals).

           

            Corals require shallow, clear water at temps above 65 degrees F.