Chapter 13 Ocean Motions Wave Action How Waves

Chapter 13 – Ocean Motions

Wave Action

How Waves Form • Most waves form when winds blowing across the water’s surface transmit their energy to the water.

Wave Size Depends on: 1. The strength of wind that is blowing. 2. The length of time the wind blows. 3. The distance the wind blows.

Describing Waves

Particle Motion • Although waves appear to carry water toward shore, the water does not actually move forward in deep water. • Particles move in larger circles closer to the surface and smaller circles deeper. • At a depth of ½ the wavelength water particles are not affected by the wave action.

How Waves Change Near Shore • Waves “feel the bottom” • As a wave approaches the shore the water becomes shallower and the wave grows taller. • Near shore = wave height increases and wavelength decreases

• Further out at sea, the wave height is smaller and the wavelength is larger.

How Waves Affect the Shore • As waves come onto shore, water washes up the beach at an angle, carrying sand grains with it. • The water and sand then run straight back down the beach. • This movement of sand along the beach is called a longshore drift.

• As waves slow down, they deposit the sand they are carrying on the shallow, underwater slope in a long ridge called a sand bar.

• As the waves slow down they deposit the sand they are carrying on the shallow, underwater slope in a long ridge called a sandbar.

• One way to prevent longshore drift and beach erosion is to build a wall of rocks and concrete stretching from the beach into the ocean called a groin.

Rip Current • As a sandbar grows, it can trap the water flowing along shore. In some places the water will break free creating a rip current. • A rip current is a rush of water that flows rapidly back to sea through a narrow opening.

Tides

Tides • A tide is the daily rise and fall of Earth’s waters on its coastlines. • Tides are unlike surface waves because they occur no matter how the wind blows. • Tides occur in all bodies of water (most noticeable in large lakes & oceans).

Tides • Tides are caused by the interaction of Earth, the moon, and the sun via the effects of gravity. • High tides occur about 12 hours and 25 minutes apart at each place.

Spring Tides – occurs 2 times a month when moon and sun are aligned during the new moon and full moon. – Their gravitational pull creates the greatest range between high and low tides.

Spring Tides

Neap Tides – occurs 2 times a month when the moon and sun pull at right angles to each other during the 1 st and 3 rd Quarter moon. – Their line-up creates the least difference between low and high tides.

Neap Tides

• Scientists can predict the tides. They produce tide tables for the public to use. • The movement of huge amounts of water between high and low tide are a source of potential energy (that is stored & waiting to be used).

• Tidal power plants capture tidal energy as the tides move in and out. • Harnessing tidal power is practical only where there is a large difference between high and low tides at least 4 meters apart.

Ocean Water Chemistry

The Salty Ocean • One kilogram of ocean water contains about 35 grams of salt. • The total amount of dissolved salts in water is called salinity.

The Salty Ocean • The substance you know as table salt, sodium chloride, is the salt in the greatest amount in ocean water.

The Salty Ocean

The Salty Ocean • Evaporation increases salinity, since salt is left behind as the water evaporates. • Salinity affects several properties of ocean water: – Drops freezing point to -1. 9°C – Higher density (allowing objects to float easily)

Gases in Ocean Water • Carbon dioxide and oxygen are found in the ocean. • Oxygen in seawater comes from the atmosphere and from algae in the ocean. • More oxygen near the surface. • More Carbon dioxide in the ocean than in the atmosphere.

The Temperature of Ocean Water • Because warm water is less dense than cold water, this warm water stays as a layer near the surface. • The temperature of water affects the amount of dissolved oxygen it can hold.

Changes with Depth • The temperature decreases as you descend through the water column. • Pressure increases the further down you go. (As much as 400 times greater than the surface).

Observation • Scientists can observe and study the ocean floor by using submersibles. • Submersibles are built very strong to resist the effects of pressure.

Currents and Climate

Surface Currents • A current is a large stream of water that flows through the oceans. • Unlike waves: – Carries water from one place to another (great distances)

Surface Currents • Surface currents, affect water to a depth of several hundred meters, are driven mainly by winds.

Surface Currents • Why do currents move in circular patterns? – Earth’s rotation causes the path of winds and currents to curve. – Coriolis Effect is the effect of Earth’s rotation on the direction of winds are currents.

Surface Currents • The largest and powerful surface current in the North Atlantic Ocean, is the Gulf Stream. • It is caused by strong winds from the west.

Surface Currents & Climate • Climate is the pattern of temperature & precipitation of an area for a long period of time.

Surface Currents & Climate • Currents affect climate by moving cold and warm water around the globe. • Currents move: – warm water from tropics poles. – cold water from poles equator.

Surface Currents & Climate • A surface current warms or cools the air above it, influencing the climate of the land near the coast.

Deep Currents • At the bottom of the ocean deep currents cause the water to creep slowly across the ocean floor. • Deep currents are caused by differences in density and NOT by surface winds.

Deep Currents 1. As temperature decreases, salinity increases. 2. Water becomes denser and begins sinking. 3. Then the cold water flows back along the ocean floor as a deep water current.

Deep Currents • Deep ocean currents flow more slowly than surface currents. • Can take up to 1, 000 years to make the round trip from the pole to the equator and back again!

Upwelling • Upwelling is the upward movement of cold water from the ocean depth.

Upwelling • Upwelling brings much needed nutrients to the surface. • Because of this, they are often centers for enormous schools of fish.

El Nino • Is an abnormal climate event that occurs every 2 to 7 years in the Pacific Ocean. • El Nino can cause destructive weather (flooding, hurricanes, tornadoes, fuel forest fires, etc. )

El Nino • Knowing when it will occur can reduce its impact. • Scientists and public officials can plan emergency procedures.

Quiz Time 1. Describe how surface currents form and travel in the ocean? 2. Explain how deep currents form and move in the ocean? 3. Why are upwellings significant?

How did you do? 1. They are driven mainly by winds and follow global wind patterns in ocean basins. 2. They form when dense ocean water near the poles sinks and flows slowly along the ocean floor toward the equator.

How did you do? 3. They bring vital nutrients to surface waters that are otherwise lacking the necessary materials in which to support life.

Vocabulary Term – look up

Crest -- pg. 426 v. The highest point of a wave.

Intertidal Zone – pg. 389 v. Located between the low-tide and hightide limits.

Neritic Zone – pg. 392 v. The gently sloping section of the continental margin located between the shoreline and continental slope.

Open-Ocean or Oceanic Zone – pg. 393 v. Includes the volume of water that covers the entire sea-floor except for the continental shelf.

Trough – pg. 426 v. The lowest point of a wave.

Wave Height – pg. 426 v. The vertical distance between the crest and trough of a wave.