Chapter 10 Lecture Outline
The Restless
Oceans
Focus Question 10.1
• How does the Coriolis effect influence ocean
currents?
The Ocean’s Surface Circulation
• Ocean currents
– Masses of water that flow from one place to another
– Surface currents develop from friction between wind
and the ocean surface
– Huge, slowly moving gyres
The Ocean’s Surface Circulation
• Coriolis effect
– Deflects surface currents
• To the right in the Northern Hemisphere
• To the left in the Southern Hemisphere
– Four main currents generally exist within each
gyre
The Ocean’s Surface Circulation
• Five main gyres
1. North Pacific gyre
2. South Pacific gyre
3. North Atlantic gyre
4. South Atlantic gyre
5. Indian Ocean gyre
• Related to atmospheric circulation
The Ocean’s Surface Circulation
Ocean Circulation
The Ocean’s Surface Circulation
• Importance of surface currents on climate
– Warm currents transfer heat from low latitudes into
higher latitudes (moderating effect)
– Influence of cold currents is most pronounced in the
tropics or during summer months in the middle latitudes
• Chill the air
• Increase aridity
Focus Question 10.2
• Why is deep-ocean circulation referred to as
thermohaline circulation?
Upwelling and Deep-Ocean Circulation
• Coastal upwelling
– The rising of cold deep water to replace warm
surface water
– Wind-induced vertical movement
– Most characteristic along west coasts
– Coastal winds combined with Coriolis effect
cause water to move away from shore
Upwelling and Deep-Ocean Circulation
Ekman Spiral and Coastal Upwelling/Downwelling
Upwelling and Deep-Ocean Circulation
• Deep-ocean circulation
– A response to density differences
– Factors creating a dense mass of water
• Temperature (cold water is dense)
• Salinity (density increases with increasing salinity)
– Called thermohaline circulation
Upwelling and Deep-Ocean Circulation
• Most water in deep-ocean currents begins in
high latitudes at the surface
• A simple model of ocean circulation is a
conveyor belt traveling from the Atlantic
Ocean, through the Indian and Pacific
Oceans, and back again
Upwelling and Deep-Ocean Circulation
Focus Question 10.3
• Describe “what” interfaces at a shoreline?
The Shoreline: A Dynamic Interface
• Continental and oceanic processes converge
along coastlines
– Landscapes undergoing rapid change
– Interface between continent, ocean, and
atmosphere
• Transition zones between marine and
continental depositional environments
The Shoreline: A Dynamic Interface
• Shorelines are constantly being modified by:
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Waves and storms
Sea level change
Stream erosion and deposition
Glaciation
Volcanic activity
Tectonic forces
Human activity
The Shoreline: A Dynamic Interface
Focus Question 10.4
• Describe the motion of a floating object as a
wave passes.
Ocean Waves
• Waves
– Energy traveling along the interface between
ocean and atmosphere
– Derive energy and motion from wind
Ocean Waves
• Wave height
– Distance between a trough and a crest
• Wavelength
– Horizontal distance between successive
crests (or troughs)
• Wave period
– Time interval for one full wave to pass a fixed
position
Ocean Waves
• Wave height, length, and period depend on:
– Wind speed
– Length of time the wind blows
– Fetch (distance the wind travels)
• As the wave travels, the water passes energy in
a circular orbital motion.
Ocean Waves
Ocean Waves
• Waves are unaffected by depth until they approach shore
• Waves begin to “feel bottom” at water depth equal to wave
base
• Slightly faster waves farther out to sea catch up and
decrease the wavelength, which causes the wave to grow
steadily higher
• When the wave is too steep to support itself, the wave
front collapses, or breaks
• Surf is turbulent water created by breaking waves
Ocean Waves
Focus Question 10.5
• Why do waves approaching the shoreline
often bend?
Beaches and Shoreline Processes
• Beaches are composed of whatever
material is available
– Some have a significant biological
component
– Material does not stay in one place
• Wave erosion
– Caused by wave impact and pressure
– Breaks down rock, supplying sand to
beaches
Beaches and Shoreline Processes
Beaches and Shoreline Processes
• Rivers of sand
– Sand in the surf zone moves roughly parallel to the
shoreline
– Wave energy causes sand to move perpendicular to
the shoreline
• Wave refraction
– Bending of waves
– As waves first touch bottom in the shallows they are
slowed, causing them to bend
– Wave arrives parallel to shore
Beaches and Shoreline Processes
• Wave refraction
– Wave energy is concentrated against the sides and
ends of the headland
– Wave erosion straightens an irregular shoreline
Wave Motion and Wave Refraction When Approaching
Shore
Beaches and Shoreline Processes
• Longshore transport
– Beach drift
• Sediment moves in a zigzag pattern along the beach face
– Longshore current
• Current in surf zone
• Parallel to shore
• Moves substantially more sediment than beach drift
Beaches and Shoreline Processes
Beach Drifting and Longshore Currents
Focus Question 10.6
• Describe erosional and depositional shoreline
features.
Shoreline Features
• Erosional features
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Wave-cut cliff
Wave-cut platform
Marine terraces
Associated with headlands
• Sea arch
• Sea stack
Shoreline Features
Shoreline Features
Shoreline Features
• Depositional features
– Spit
• A ridge of sand extending from the land into a bay with a
hooked end
– Baymouth bar
• A sand bar that completely crosses a bay
– Tombolo
• A ridge of sand that connects an island to the mainland or
another island
Shoreline Features
Shoreline Features
• Barrier islands
– Mainly along the Atlantic and Gulf Coasts
– Parallel the coast
– Originate in several ways:
• As spits severed from the mainland
• Created when turbulent waters heaped up sand scoured from
the bottom
• Former sand-dune ridges that originated along the shore
during the last glacial period
Shoreline Features
Shoreline Features
Focus Question 10.7
• How permanent are hard stabilization efforts
along shorelines?
Stabilizing the Shore
• Shoreline erosion influenced by local factors:
– Proximity to sediment-laden rivers
– Degree of tectonic activity
– Topography and composition of
the land
– Prevailing wind and weather patterns
– Configuration of the coastline
Stabilizing the Shore
• Responses to erosion problems
– Hard stabilization—Building structures
• Groins
– Barriers built at a right angle to the beach
– Designed to trap sand
• Breakwaters
– Barriers built offshore and parallel
– Protect boats from breaking waves
Stabilizing the Shore
Stabilizing the Shore
• Seawalls
– Armors the coast against breaking waves
• Often not effective
Stabilizing the Shore
• Alternatives to hard stabilization
– Beach nourishment by adding sand to the beach
system
– Relocating buildings away from beach
Focus Question 10.8
• How might building a dam on a river that
flows to the sea affect a beach?
Contrasting America’s Coasts
• Erosion problems along U.S. Coasts
– Shoreline erosion problems are different along the
opposite coasts
– Atlantic and Gulf Coasts
• Development occurs mainly on barrier islands
– Face open ocean
– Receive full force of storms
• Development taken place more rapidly than understanding
barrier island dynamics
Contrasting America’s Coasts
Contrasting America’s Coasts
• Erosion problems along U.S. Coasts
– Pacific Coast
• Characterized by relatively narrow beaches
backed by steep cliffs and mountain ranges
• Major problem is the narrowing of the beaches
– Sediment for beaches is interrupted by dams and
reservoirs
– Rapid erosion occurs along the beaches
Contrasting America’s Coasts
• Shoreline classification is based on changes
with respect to sea level
– Emergent coast
• Uplift of the land, or
• A drop in sea level
Contrasting America’s Coasts
Submergent coast
• Land adjacent to sea subsides, or
• Sea level rises
– Features of a submergent coast
• Highly irregular shoreline
• Estuaries
- Drowned river mouths
Contrasting America’s Coasts
Focus Question 10.9
• Explain why an observer can experience two
unequal high tides during one day.
Tides
• Changes in elevation of ocean surface
• Caused by the gravitational forces exerted
upon Earth by the Moon, and to a lesser
extent by the Sun
Tides
Tides
• Spring tide
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During new and full moons
Gravitational forces added together
Especially high and low tides
Large daily tidal range
Tides
• Neap tide
– First and third quarters of the Moon
– Gravitational forces are offset
– Daily tidal range is least
Tides
• Tidal patterns
– Many factors influence the tides:
• Shape of the coastline
• Configuration of the ocean basin
• Water depth
– Diurnal pattern
– Semidiurnal pattern
– Mixed pattern
Tides
• Diurnal tidal pattern
– A single high and low tide each tidal day
– Occurs along northern shore of Gulf of Mexico
• Semidiurnal tidal pattern
– Two high and low tides each tidal day
– Little difference in high and low water heights
• Mixed tidal pattern
– Two high and two low waters each day
– Large inequality in high water heights, low water heights, or
both
– Prevalent along the Pacific Coast of the United States
Tides
Tidal Cycle
Tides
• Tidal currents
–Horizontal flow accompanying the rise and
fall of tides
–Flood current
• Advances into the coastal zone
–Ebb current
• Seaward moving water
–Sometimes tidal deltas are created
Tides