Earth Science,
Chapter 13: The Restless Ocean
I. Ocean water movements
A. Surface circulation
1.Ocean currents are masses of water that flow from one place to another
2. Surface currents develop from friction between the ocean and the wind that blows
across the surface
3. Huge, slowly moving gyres
3. Five main gyres
4. Related to atmospheric circulation
5. Deflected by the Coriolis effect
a. To the right in the Northern Hemisphere
b. To the left in the Southern Hemisphere
6. Four main currents generally exist within each gyre
7. Importance of surface currents
a. Climate
1. Currents from low latitudes into higher latitudes (warm currents) transfer
heat from warmer to cooler areas
2. Influence of cold currents is most pronounced in the tropics or during the
summer months in the middle latitudes
b. Upwelling
1. The rising of cold water from deeper layers
2. Most characteristic along west coasts of continents
3. Brings greater concentrations of dissolved nutrients to the ocean surface
B. Deep-ocean circulation
1. A response to density differences
2. Factors creating a dense mass of water
a. Temperature – cold water is dense
b. Salinity – density increases with increasing salinity
3. Called thermohaline circulation
4. Most water involved in deep-ocean currents begins in high latitudes at the surface
5. A simplified model of ocean circulation is similar to a conveyor belt that travels
from the Atlantic Ocean, through the Indian and Pacific Oceans and back again
C. Waves
1. Energy traveling along the interface between ocean and atmosphere
2. Derive their energy and motion from wind
3. Parts
a. Crest
b. Trough
4. Measurements of a wave
a. Wave height – the distance between a trough and a crest
b. Wavelength – the horizontal distance between successive crests (or troughs)
c. Wave period – the time interval for one full wave to pass a fixed position
5. Wave height, length, and period depend on
a. Wind speed
b. Length of time the wind blows
c. Fetch – the distance that the wind travels
6. As the wave travels, the water passes energy along by moving in a circle
a. Waveform moves forward
b. At a depth of about one-half the wavelength, the movement of water particles
becomes negligible (the wave base)
II. Beaches and shoreline processes
A. Beaches are composed of whatever material is available
1. Some beaches have a significant biological component
2. Material does not stay in one place
B. Wave erosion
1. Caused by
a. Wave impact and pressure
b. Abrasion by rock fragments
2. Breaks down rock material and supplies sand to beaches
C. Wave refraction
a. Bending of a waves
b. Wave arrives parallel to shore
c. Results
1. Wave energy is concentrated against the sides and ends of headland
2. Wave erosion straightens an irregular shoreline
D. Longshore transport
a. Beach drift – sediment moves in a zigzag pattern along the beach face
b. Longshore current
1. Current in surf zone
2. Flows parallel to the shore
3. Moves substantially more sediment than beach drift
III. Shoreline features
A. Erosional features
1. Wave-cut cliff
2. Wave-cut platform
3. Marine terraces
4. Associated with headlands
a. Sea arch
b. Sea stack
B. Depositional features
1. Spit – a ridge of sand extending from the land into the mouth of an adjacent bay with
an end that often hooks landward
2. Baymouth bar – a sand bar that completely crosses a bay
3. Tombolo – a ridge of sand that connects an island to the mainland
4. Barrier islands
a. Mainly along the Atlantic and Gulf Coastal Plains
b. Parallel the coast
c. Originate in several ways
IV. Stabilizing the shore
A. Shoreline erosion is influenced by the local factors
1. Proximity to sediment-laden rivers
2. Degree of tectonic activity
3. Topography and composition of the land
4. Prevailing wind and weather patterns
5. Configuration of the coastline
B. Responses to erosion problems
1. Hard stabilization - building structures
a. Types of structures
1. Groins
a. Barriers built at a right angle to the beach
b. Trap sand
2. Breakwaters
a. Barriers built offshore and parallel to the coast
b. Protects boats from the force of large breaking waves
3. Seawalls
a. Armors the coast against the force of breaking waves
b. Stops waves from reaching the beach areas behind the wall
b. Often these structures are not effective
2. Alternatives to hard stabilization
a. Beach nourishment by adding sand to the beach system
b. Relocating buildings away from beach
C. Erosion problems along U.S. Coasts
1. Shoreline erosion problems are different along the opposite coasts
2. Atlantic and Gulf Coasts
a. Development occurs mainly on barrier islands
1. Face open ocean
2. Receive full force of storms
b. Development has taken place more rapidly than our understanding of barrier
island dynamics
3. Pacific Coast
a. Characterized by relatively narrow beaches backed by steep cliffs and mountain ranges
b. Major problem is the narrowing of the beaches
1. Sediment for beaches is interrupted by dams and reservoirs
2. Rapid erosion occurs along the beaches
V. Coastal classification
A. Shoreline classification is difficult
B. Classification based on changes with respect to sea level
1. Emergent coast
a. Caused by
1. Uplift of the land, or
2. A drop in sea level
b. Features of an emergent coast
1. Wave-cut cliffs
2. Marine terraces
1. Submergent coast
a. Caused by
1. Land adjacent to sea subsides, or
2. Sea level rises
b. Features of a submergent coast
1. Highly irregular shoreline
2. Estuaries – drowned river mouths
VI. Tides
A. Changes in elevation of the ocean surface
B. Caused by the gravitational forces exerted upon the Earth by the
1. Moon, and to a lesser extent by the
2. Sun
C. Monthly tidal cycle
1. Spring tide
a. During new and full moons
b. Gravitational forces added together
c. Especially high and low tides
d. Large daily tidal range
2. Neap tide
a. First and third quarters of the Moon
b. Gravitational forces are offset
c. Daily tidal range is least
D. Tidal patterns
1. Many factors influence the tides
a. Shape of the coastline
b. Configuration of the ocean basin
c. Water depth
2. Main tidal patterns
a. Diurnal tidal pattern
1. A single high and low tide each tidal day
2. Occurs along the northern shore of the Gulf of Mexico
b. Semidiurnal tidal pattern
1. Two high and two low tides each tidal day
2. Little difference in the high and low water heights
3. Common along the Atlantic Coast of the U.S.
c. Mixed tidal pattern
1. Two high and two low waters each day
2. Large inequality in high water heights, low water heights, or both
3. Prevalent along the Pacific Coast of the U.S.
3. Tidal currents
a. Horizontal flow accompanying the rise and fall of tides
b. Types of tidal currents
1. Flood current – advances into the coastal zone
2. Ebb current – seaward moving water
c. Sometimes tidal deltas are created by tidal currents
Notes Take from the Tarbuck and Lutgens Website