The Oceans and Atmosphere




The Oceans and Atmosphere


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The Oceans and Atmosphere


The Oceans and Atmosphere

The shoreline - a dynamic interface

The shoreline is a dynamic interface (boundary) between air, land, and the ocean

The shoreline is constantly being modified by waves

Today the coastal zone is experiencing intense human activity


Characteristics of Waves

Generated by wind

Parts of a wave

Crest – top of the wave

Trough – low area between waves

Measurements of a wave

Wave height – the distance between a trough and a crest

Wavelength – the horizontal distance between crests

Wave period – the time interval between the passage of two successive crests




Wave parts and the movement of water particles

Particle Movement with Wave Passage

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

Types of waves

Wave of oscillation

Wave energy moves forward, not the water itself

Occur in the open sea in deep water

Wave of translation

Begins to form in shallower water when the water-depth is about one-half the wavelength and the wave begins to “feel bottom”

As the speed and length of the wave diminish, the wave grows higher

The steep wave front collapses and the wave breaks along the shore

Turbulent water advances up the shore and forms surf


Changes that occur when a wave moves onto shore


Wave erosion

Breaking waves exert a great force

Wave erosion is caused by

Wave impact and pressure

Abrasion by rock fragments

Cliff undercut by wave erosion along the Oregon coast

Wave refraction and longshore transport

Wave refraction

Bending of a wave

Causes waves to arrive nearly parallel to the shore

Consequences of wave refraction

Wave energy is concentrated against the sides and ends of headlands

If the shoreline remains stable, the result of shoreline erosion and deposition is to eventually produce a straighter coast


Refraction of waves

Wave refraction and longshore transport


Wave refraction

Moving sand along the beach

Oblique waves also produce longshore currents

Currents in the surf zone

Flow parallel to the coast

Easily moves fine suspended sand and rolls larger sand and gravel along the bottom


Movement of sand by longshore current


Shoreline features

Features vary depending on several factors including

The rocks along the shore


Wave intensity

Whether the coast is stable, sinking, or rising


Features caused by wave erosion

Wave-cut cliffs

Wave-cut platform

Features associated with headlands

Sea arch

Sea stack


Wave Erosion


Anacapa Island

Sea stack


Features related to beach drift and longshore currents

Baymouth bar – a sand bar (spit) that completely crosses a bay

Tombolo – a ridge of sand that connects an island to the mainland or another island



Massachusetts coast Depositional features

Shoreline features

Barrier islands

Mainly along the Atlantic and Gulf coasts

Low ridges of sand that parallel the coast 3 to 30 kilometers offshore

Probably form in several ways

Barrier islands along the Texas coast

Shoreline erosion problems

Shoreline erosion is influenced by several local factors including

Proximity to sediment-laden rivers

Degree of tectonic activity

Topography and composition of the land

Prevailing wind and weather patterns

Configuration of the coastline and near-shore areas

Three basic responses to erosion problems

1.  Building structures


Usually built in pairs to develop and maintain harbors

Extend into the ocean at the entrances to rivers and harbors

Jetties prevent deposition in channels

Three basic responses to erosion problems

1.  Building structures


Built to maintain or widen beaches

Constructed at a right angle to the beach to trap sand

Three basic responses to erosion problems

1.  Building structures


Barrier built offshore and parallel to the coast

Protects boats from the force of large breaking waves

Three basic responses to erosion problems

1.  Building structures


Barrier parallel to shore and close to the beach to protect property

Stops waves form reaching the beach areas behind the wall

Often the building of structures is not an effective means of protection

Three basic responses to erosion problems

2.  Beach nourishment

The addition of large quantities of sand to the beach system

Only an economically viable long-range solution in a few areas

3.  Abandonment and relocation of buildings away from the beach

An Underfed Beach

After Beach Nourishment


Contrasting the Atlantic and Pacific Coasts

Shoreline erosion problems are different along the opposite coasts

Atlantic and Gulf Coasts

Broad, gently sloping coastal plains

Tectonically quiet regions

Contrasting the Atlantic and Pacific Coasts

Atlantic and Gulf Coasts

Development occurs mainly on the barrier islands (also called barrier beaches or coastal barriers)

Barrier islands face the open ocean

They receive the full force of storms

Contrasting the Atlantic and Pacific Coasts

Pacific Coast

Relatively narrow beaches backed by steep cliffs and mountain ranges

A major problem is a significant narrowing of many beaches

Shoreline erosion varies considerably from one year to the next largely because of the sporadic occurrence of storms

Emergent and submergent coasts

Emergent coasts

Develop because of uplift of an area or a drop in sea level

Features of an emergent coast

Wave-cut cliffs

Wave-cut platforms

Submergent coast

Caused by subsidence of land adjacent to the sea or a rise in sea level

Features of a submergent coast

Highly irregular shoreline

Estuaries – drowned river mouths

Chesapeake Bay is a submergent coastline



Daily changes in the elevation of the ocean surface

Causes of tides

Tidal bulges are caused by the gravitational forces of the Moon, and to a lesser extent the Sun


Tides are caused by gravitational forces of the Moon

Spring and neap tides

Spring tides

Occur during new and full moons

Gravitational forces of the Moon and Sun are added together

Especially high and low tides

Large daily tidal range

The Moon and Earth during spring tides

Spring and neap tides

Neap tides

Occur during the first and third quarters of the Moon

Gravitational forces of the Moon and Sun are offset

Daily tidal range is least

The Moon and Earth during neap tides

Other factors that influence tides

Shape of the coastline

Configuration of the ocean basin

Tidal currents

Horizontal flow of water accompanying the rise an fall of the tide

Tidal currents

Types of tidal currents

Flood current – advances into the coastal zone as the tide rises

Ebb current – seaward-moving water as the tide falls

Areas affected by the tidal currents are called tidal flats

Occasionally form tidal deltas




Tidal flats and a tidal delta


The Ocean Floor
The vast world ocean

Earth  is often referred to as the water planet

71% of Earth’s surface is represented by oceans

Continents and islands comprise the remaining 29% 

Northern Hemisphere is called the land hemisphere, and the Southern Hemisphere the water hemisphere


Distribution of land and water

Distribution of land and water


Extra-Terrestrial Water




Mapping the ocean floor

Depth was originally measured by lowering weighted lines overboard (sounding)

Echo sounder (also referred to as sonar)

Sound navigation and ranging

Invented in the 1920s

Primary instrument for measuring depth

Reflects sound from ocean floor 

Multibeam sonar

Employs an array of sound sources and listening devices

Obtains a profile of a narrow strip of seafloor

Echo sounders (A) and multibeam sonar (B)

Three major topographic units of the ocean floor

Continental margins

Deep-ocean basins

Mid-ocean ridges


Major topographic divisions of the North Atlantic Ocean

Passive Continental margins

Found along most coastal area that surround the Atlantic Ocean

Not associated with plate boundaries

Experience little volcanism and few earthquakes

Features comprising a passive continental margin

Continental shelf

Flooded extension of the continent

Varies greatly in width

Gently sloping

Contain important mineral deposits

Some areas are mantled by extensive glacial deposits 


Features comprising a passive continental margin

Continental slope

Marks the seaward edge of the continental shelf

Relatively steep structure

Boundary between continental crust and oceanic crust

Features comprising a passive continental margin

Continental rise

Found in regions where trenches are absent

Continental slope merges into a more gradual incline – the continental rise

Thick accumulation of sediment

At the base of the continental slope turbidity currents deposit sediment that forms deep-sea fans


Submarine canyons and turbidity currents

Submarine canyons

Deep, steep-sided valleys cut into the continental slope

Some are extensions of river valleys

Most appear to have been eroded by turbidity currents


Turbidity currents

Downslope movements of dense, sediment-laden water

Deposits are called turbidites

Turbidites are layered and exhibit graded bedding (decrease in sediment grain size from bottom to top)


Submarine canyons are eroded by turbidity currents

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

An active continental margin

Features of the deep-ocean basin

Deep-ocean trench

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

The world’s major oceanic trenches


Abyssal plains

Likely the most level places on Earth

Sites of thick accumulations of sediment

found in all oceans


Isolated volcanic peaks

Many form near oceanic ridges

May emerge as an island

May sink and form flat-topped seamounts called guyots

Mid-ocean ridges

Characterized by elevated topography, extensive faulting, and volcanic activity

Interconnected ridge system is the longest topographic feature on Earth’s surface

Along the axis of some segments are deep down-faulted structures called rift valleys

Consist of layer upon layer of basaltic rocks that have been faulted and uplifted


Coral reefs and atolls

Coral reefs

Constructed primarily from skeletal remains and secretions of corals and certain algae

Confined largely to the warm, clear waters of the Pacific and Indian Oceans

Examples of Coral


Coral islands – a continuous ring of coral reef surrounding a central lagoon

Form on the flanks of a sinking volcanic island (hypothesis proposed by Charles Darwin)

Formation of a coral atoll

Atolls in the Pacific

Key Terms Chapter 12



Tides (ebb, flood, spring, neap)

Tidal delta

Waves, surf

Longshore currents, transport

Beach drift, beach erosion

Wave-cut cliff


Baymouth bar


Barrier island

Emergent coastline, elevated wave-cut terrace

Submergent coastline, estuary

Continental shelf, slope, rise

Abyssal plain

Mid-ocean ridge


Greenhouse effect

Ozone layer

Coriolis effect


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