The Restless Ocean
Chapter 10 Lecture
Natalie Bursztyn
Utah State University
Foundations of Earth Science
Eighth Edition
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Discuss the factors that create and influence ocean currents.
Describe the influence ocean currents have on climate.
Focus Questions 10.1
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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 Pattern of Ocean Currents
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Five main gyres
North Pacific gyre
South Pacific gyre
North Atlantic gyre
South Atlantic gyre
Indian Ocean gyre
Related to atmospheric circulation
The Pattern of Ocean Currents
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The Pattern of Ocean Currents
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Coriolis effect
Result of the Earth’s rotation
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 Pattern of Ocean Currents
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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
Ocean Currents Influence Climate
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Ocean Currents Influence Climate
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Ocean Currents Influence Climate
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Explain the processes that produce coastal upwelling the ocean’s deep circulation.
Focus Question 10.2
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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
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Coastal Upwelling
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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
Deep-Ocean Circulation
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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
Deep-Ocean Circulation
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Deep-Ocean Circulation
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Explain why the shoreline is considered a dynamic interface.
List the factors that influence the height, length, and period of a wave.
Describe the motion of water within a wave.
Focus Questions 10.3
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Continental and oceanic processes converge along coasts
Landscapes undergoing rapid change
Interface (common boundary where different parts of a system interact) between continent, ocean, and atmosphere
Transition zones between marine and continental depositional environments
The Shoreline: A Dynamic Interface
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Shorelines are constantly being modified by:
Waves and storms
Sea level change
Stream erosion and deposition
Glaciation
Volcanic activity
Tectonic forces
Human activity
A Dynamic Interface
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A Dynamic Interface
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Waves
Energy traveling along the interface between ocean and atmosphere
Derive energy and motion from wind
Ocean Waves
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Wave height
Vertical 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
Wave Characteristics
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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.
Wave Characteristics
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Circular Orbital Motion
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Waves in the Surf Zone
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
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Ocean Waves
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Describe how waves erode and move sediment along the shore.
Focus Question 10.4
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Beaches are composed of whatever material is available
Some have a significant biological component
Material does not stay in one place
Beaches and Shoreline Processes
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Beaches and Shoreline Processes
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Wave erosion
Caused by wave impact and pressure
Breaks down rock, supplying sand to beaches
Abrasion is the sawing and grinding action of water armed with rock fragments
Wave Erosion
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Wave Erosion
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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
Sand Movement on the Beach
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Wave refraction
Wave energy is concentrated against the sides and ends of the headland
Wave erosion straightens an irregular shoreline
Sand Movement on the Beach
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Sand Movement on the Beach
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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
Sand Movement on the Beach
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Beaches and Shoreline Processes
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Describe the features typically created by wave erosion and those resulting from sediment deposited by longshore transport processes.
Focus Question 10.5
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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
Shoreline Features
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Wave-cut cliff
Wave-cut platform
Marine terraces
Associated with headlands
Sea arch
Sea stack
Erosional Features
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Erosional Features
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Erosional Features
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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
Depositional Features
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Depositional Features
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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
Depositional Features
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Depositional Features
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The Evolving Shore
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Distinguish between emergent and submergent coasts.
Contrast the erosion problems faced along different parts of America’s coast.
Focus Questions 10.6
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Erosion problems along U.S. Coasts
Shoreline erosion problems are different along the opposite coasts
Contrasting America’s Coasts
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Shoreline classification is based on changes with respect to sea level
Emergent coast
Uplift of the land, or
A drop in sea level
Coastal Classification
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Submergent coast
Land adjacent to sea subsides, or
Sea level rises
Features of a submergent coast
Highly irregular shoreline
Estuaries
Drowned river mouths
Coastal Classification
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Coastal Classification
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Erosion problems along U.S. 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
Atlantic and Gulf Coasts
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Atlantic and Gulf Coasts
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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
Pacific Coast
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Pacific Coast
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Summarize the ways in which people deal with shoreline erosion problems.
Focus Question 10.7
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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
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Hard Stabilization
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Seawalls
Armors the coast against breaking waves
Often not effective
Hard Stabilization
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Beach nourishment by adding sand to the beach system
Relocating buildings away from beach
Alternatives to Hard Stabilization
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Explain the cause of tides as well as their monthly cycles and other patterns.
Describe the horizontal flow of water that accompanies the rise and fall of the tides.
Focus Questions 10.8
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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
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Tides
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Spring tide
During new and full moons
Gravitational forces added together
Larger tidal troughs and tidal bulges
Large daily tidal range
Monthly Tidal Cycle
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Neap tide
First and third quarters of the Moon
Gravitational forces are offset
Daily tidal range is least
Monthly Tidal Cycle
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Many factors influence the tides:
Shape of the coastline
Configuration of the ocean basin
Water depth
Diurnal pattern
Semidiurnal pattern
Mixed pattern
Tidal Patterns
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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
Tidal Patterns
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Tidal Patterns
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Horizontal flow accompanying the rise and fall of tides
Flood current
Advances into the coastal zone
Ebb current
Seaward moving water
Tidal flats are alternatively covered and uncovered by tides
Sometimes tidal deltas are created
Tidal Currents
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Tidal Currents
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