Earth Science, 10^th edition

Chapter 14: The Dynamic 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

             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

             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

       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

 

  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

 

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

 

 

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