1. 9.2 Ocean Waves, Tides and Currents

2. Wave Characteristics
Most ocean waves are energy passing through water caused by the wind
Crests are the top of the waves
Troughs are the bottom of the waves

3. Wave Characteristics
Wave Height is the vertical distance between trough and crest
Wavelength is the horizontal distance between two crests or two troughs
Wave period is the time one wave takes to pass a fixed position.

4. Wave Characteristics
The height, length, and period of a wave depends of three factors:
Wind speed
Length of time the wind has blown
Fetch, or the distance that the wind has traveled across open water

5. Wave Motion Waves can travel great distances across ocean basins
The energy of the wave, not the water itself, travels across the ocean
Circular orbital motion allows energy to move through the water, water particles move in circles
Energy is moved across the ocean as well as downward

6. Breaking Waves In deep water waves are unaffected by depth
In shallow water waves speed slows down causing waves farther out to catch up
Speed and length decrease, wavelength shortens, the wave grows higher
When wave is too high to support itself, it collapses
Turbulent water created by breaking waves is called surf

7. Tides Tides are regular changes in the elevation of the ocean surface
The pull of gravity from the moon and, to a lesser extent by the sun, creates tides
The pull of gravity of the moon and sun is greater on the Earth that’s nearest the source of gravity

8. The Cause of Tides
The difference in gravitational pull on Earth closest and farthest from the moon stretches the Earth
Inertia is the property of an object that is in motion to stay in motion, and an object at rest to stay at rest
Due to inertia ocean water flows towards both areas - closest and farthest from the moon - creating a tidal bulge, or high tide
Question: What causes the high tides on both sides of the Earth?
Answer: Inertia!

9. Tidal Cycle
Spring tides are when the sun and moon are aligned, their forces of gravity creates larger tidal bulges
Spring tides happen during new and full moons
Neap tides are when the sun and moon are not aligned, their forces off-set each other, creating small tidal bulges
Question: Do Spring tides happen only in the Spring?
Answer: No they happen twice every month.

10. Tidal Patterns
Many factors effect tides, such as shape of the coastline, the ocean basins, and water depth
Three main tidal patters:
Diurnal tides – single high tide and single low tide each tidal day
Semidiurnal tide – two high tides and two low tides each tidal day
Mixed tide – Usually two high and two low tides, however heights are varied. (Our tides here on the Pacific Coast)
Question: Name the factors that effect tides.
Answer: Moon and sun’s position; day in the tidal cycle; shape of coastline; ocean basin; and water depth.

11. OCEAN SURFACE CIRCULATION
Ocean currents - masses of ocean water that flows from one place to another
Surface currents – water that flows horizontally in the upper part of the ocean’s surface
Developed from friction between the ocean and wind that blows across its surface

12. Gyres
Gyres – Large circular currents moving water in a circular motion on the ocean’s surface in an ocean basin
5 main ocean gyres: North Pacific Gyre, South Pacific Gyre, North Atlantic Gyre, South Atlantic Gyre, Indian Ocean Gyre
Pair Share: What do you think the red and blue lines represent?
Answer: Red - warm water, Blue - cold water

13. Coriolis Effect
Coriolis effect – the deflection of currents away from their original course as a result of Earth’s rotation
Flow in opposite directions in the two different hemispheres

14. Ocean Currents and Climate
Ocean currents effect climate by transferring heat from one area to another
When water flows from the equator to the poles the warm water heats the atmosphere.
Some countries such as England have warmer weather because of ocean currents.

15. DEEP-OCEAN CIRCULATION
Deep-Ocean Currents – water that flows vertically mixing deep & surface water caused by differences in density
Upwelling – The rising of cold water from deeper layers to replace warmer surface water
Important in providing nutrients to sea life

16. Sources of currents Deep currents are:
found primarily in high latitudes (poles) at the surface.
created from increased salinity of ocean water due to evaporation.
Question: Why is the warm water shallow & the cold water deep?
Answer: Colder water is denser and sinks below warm water
Conveyor Belt model