Ocean Currents

Currents and Climate Zones

Ocean Currents

The water in the ocean is always moving. When we look at the surface we see the water moving in waves, but when we look below the surface, the water moves in large currents. These are called ocean currents. Ocean current is a nonstop flow of water in the ocean hundreds of feet below the surface of the water. These currents strongly impact the climates of nearby land. There are two types of ocean currents; warm and cold. Warm ocean currents moisten the air above the surface producing rain. Whereas cold ocean currents cool the air above the surface creating deserted areas.

Bill Nye The Science Guy on Ocean Currents (oceanography (Full Clip)

Energy Transfer in the Oceans

When the water works its way towards the poles, it gets colder and more salty. This causes the surface to evaporate and form sea ice. Sea water discards any salt when it freezes which is why it’s mostly all fresh water. Because of this, the remaining water becomes saltier. Two factors that result the water at the poles to be denser is low temperature and saltiness. This causes the water to sink to the ocean floor.

Warmer surface water from the equator then flows toward the poles to take its place. This process is called the thermohaline circulation-continuous flow of water around the world's oceans driven by the differences in water temperatures and salinity-of the oceans.

Ocean currents around the world act like a giant conveyor belt, from the equator to the pole.

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Ocean Water Properties

What impacts ocean currents?

  1. Temperature- the heat rises
  2. Salinity- salty water sinks
  3. Density- a function of temperature and salinity


Differences in the density of water can also cause currents to form and move. Density is affected by temperature and salinity. Cold water or water with dissolved salts (higher salinity) is denser than warm water or water without dissolved salts (low or no salinity)

Primary Current Forces

What makes the water move?


  1. Solar Heating- causes water to expand and move
  2. Wind- pushes the water; the wind blows for 10 hours across the ocean and causes the surface of the water to flow at 2 percent of the wind speed. (Wind has the greatest affect on surface currents.)
  3. Gravity- pulls the water downhill or piles against the pressure influencing tides
  4. Coriolis Force/Effect- this is the force caused by the earth's rotation. It causes moving bodies to be turned aside to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The Force is relative to the speed and latitude of the moving object. It is zero at the equator and maximum at the poles.

Continental Drift

According to the theory of plate tectonics, the earth's continents have moved over the surface of the globe for hundreds of millions of years. This movement is called the continental drift. One super continent split up into smaller continents as we see today. This movement took place over the course of 225 million years.

When continents move, it effects the ocean currents and wind patterns. The pattern of the air and ocean currents is not the same as it was millions of years ago.

Pangea Breakup and Continental Drift Animation

Thinking Questions

  • What is the path that the global ocean conveyor takes?
  • What affects the flow of water in the oceans?
  • Why is the global ocean conveyor important for the health of the oceans and the marine life in them?
  • What are some possible scenarios if the global conveyor stops completely?