Ocean Currents and Tides
What is the difference between a tide and a current?
Currents
Surface currents
Driven by wind blowing across water
Affected by the Coriolis effect
N. Hemisphere (right) vs S. Hemisphere (left)
Currents flow perpendicular to wind
Ekman spiral
Deep ocean currents
Driven by density differences (temp and salinity)
Creates deep ocean circulation (thermohaline circulation)
Warm water flows towards poles…cool and sinks…returns to equator…upwells to replace warm water flowing to the poles
Tides
Daily changes in the elevation of the ocean
What causes tides to occur
Diurnal, semidiurnal and cyclic tides occur depending on your location in the world
what is a spring tide? What is a neap tide
Beach Processes
What are some common features of beaches?
Do we see all these features at every beach?
Why are there different features at different beaches?
Sand or Rock
What controls what will occur (sand or rock) at any particular beach?
Different types of sands at different beaches
What is available to make the sand
Olivine
Basalt
Shells
Quartz
Etc….
Waves
What causes waves?
Solar radiation--> warms atmosphere-->creates wind--> friction of wind creates waves
Waves transfer energy
What controls the size, period and speed of waves?
Wave motion
Ocean waves have oscillatory motion
What happens when waves approach the shoreline?
Translational motion
Breakers
Swash and Backwash
Wave refraction
waves approach shoreline at angle
wave bends as it approaches shoreline
causes longshore current
longshore drift
Erosion vs Deposition
Which will dominate?
Where the waves break
big shelf vs small shelf
What type of continental shelf does
High erosion in the winter
Low erosion in the summer
Wave erosion
Waves expend energy on the shoreline
Amount of erosion depends on what factors?
Erosional Features
Wave cut benches or platforms
Headlands
Sea Stacks
Stopping Erosion?
Why would we want to?
Methods used for slowing erosion
Breakwaters
Structure that is parallel to shoreline
Groins & Jetties
Right angle to beach
Seawalls
Parallel to shoreline…right on beach
Beach nourishment
Deposition
Why does deposition occur on beaches?
When is deposition dominate on the
Beaches created by deposition of local material
Sand, coral, basalt, olivine
Longshore current creates many features
spits, baymouth bars, tombolos
Emergent vs Submergent coastlines
Emergent is when uplift is occurring
When might this happen?
What features would you see?
Submergent is subsidence
When might this happen?
What features might you see
Special features
Barrier islands
Coral reefs and Atolls
What is a coral reef?
Fringing Reef
Barrier Reef
Atoll