Currents

1
Currents

• Pgs. 70 - 77

2
Exploring Currents

• Thor Heyerdahl theorized that the inhabitants
  of Polynesia originally sailed from Peru on
  rafts powered only by the wind and ocean
  currents.
• 1947, Heyerdahl sets out to prove his theory by
  setting sail from Peru on a man-made raft.
• By day 97, Thor and his crew made it to
  Polynesia.
• Ocean currents sent their raft 6,000km west
  across the Pacific ocean.
• So if currents carried Thor over the Pacific,
  what is driving these currents?

3
Surface Currents

• Streamlike movements of water that occur at or
  near the surface of the ocean are called surface
  currents.
• Currents can be thousands of kilometers in
  length.
• The Gulf Stream is one of the longer currents
  transporting more than 25 times more water than
  all the worlds rivers.
• What controls these currents?
• Global winds, Coriolis effect, and continental
  deflections.

4
Global Winds

• The best way to visualize what global winds do,
  is to imagine you are blowing on a cup of hot
  chocolate.
• The ripples created from you are the same way the
  winds blowing across the Earths surface create
  surface currents in the ocean.
• Surface currents can go down to several hundred
  kilometers deep and several thousand kilometers
  long.
• Certain areas on the world have different
  patterns of global winds creating currents in the
  oceans.

5
Coriolis Effect

• The Earths rotation causes surface currents to
  move in curved paths rather than in straight
  lines.
• The curving of moving objects from a straight
  path due to the Earths rotation is the Coriolis
  Effects.
• To better understand the coriolis effect, imagine
  trying to roll a ball straight across a moving
  merry-go-round.

6
Continental Deflections

• If the Earths surface were covered only with
  water, the surface currents would travel freely
  across the globe in a very uniform pattern.
• The continents rise above sea level and when
  surface currents meet continents, they deflect,
  or change direction.
• Think of it like when a bouncy ball hits a wall
  and changes direction.

7
Taking Temperatures

• All three, global winds, Coriolis effect, and
  continental deflections, work together to form a
  pattern of surface currents on Earth.
• Warm currents begin near the equator.
• Cold water currents begin near the poles.
• Cold and warm water currents mix and share in all
  the oceans.

8
Deep Currents

• Streamlike movements of ocean water far below the
  surface are known as a deep current.
• Deep currents form in parts of the ocean where
  water density increases.
• Temperature and salinity combine to affect the
  density of ocean water.

9
Deep Current Formation

• At the poles of the Earth, the cold air cools the
  water and the cold water sinks down and travels
  toward the equator.
• If the ocean water freezes, ice will float on top
  of water because ice is just water while the
  ocean has many dissolved materials in it.
• It is denser with more dissolved particles in it.
• Also, in warm, tropical climates, much water is
  evaporated, making the water around it more dense
  and sink toward the bottom of the ocean.

10
Movement of Deep Currents

• Deep current movement is complex.
• Due to differences in temperature and salinity,
  the North Atlantic Deep Water flows on top of the
  denser Antarctic Bottom Water.
• The Antarctic Bottom Water is so dense that it
  takes 750 years for the water to make it to the
  equator.

11
Currents Trading Places

• The surface and deep currents exchange places
  where they meet.
• Warm water from the equator will push cold Arctic
  water down to the ocean floor.
• The cold water travels the ocean floor until it
  meets more cold water from the other pole and
  gets force to the surface to warm in temperature
  again.

12
Surface Currents and Climate

• Currents affect climate because they bring the
  temperature with it.
• Warm waters will bring warm weather and cool
  waters will bring cool weather.
• The Gulf Stream keeps the east coast warm, while
  the California current keeps the west coast cool.

13
El Nino

• Surface currents in the tropical region of the
  Pacific Ocean usually travel with the trade winds
  from east to west.
• This causes upwelling in the eastern Pacific
  ocean
• Upwelling is a process in which cold,
  nutrient-rich water from the deep ocean to rise
  and replace surface water.
• As a result the coastal waters in South America
  rise and affects the interactions of global
  weather patterns and sea-life.

14
El Nino Effects

• This phenomenon can cause floods, mudslides, and
  millions of dollar of damage to areas affected by
  it.