It’s not possible for Earth’s inhabitants to feel the planet spinning beneath their feet. Yet that movement has a profound effect on their lives. The Coriolis effect or Coriolis force refers to the deflection of an object due to the Earth’s rotation. It is thus responsible for the shape of wind and ocean currents. Many marine animals rely on currents for the dispersion and upwelling of nutrients, both of which would be very different without the Coriolis effect.
How the Coriolis Effect Works
NOAA writes on its Ocean Service Education site “Surface Ocean Currents” that if the Earth did not spin, wind would shuttle between the Equator and the Poles in a straight line. However, this planet does spin and this causes objects traveling across the globe to appear deflected towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere. Imagine an object traveling in a straight line towards the equator. Its destination will have moved by the time the object arrives at its intended spot. This can easily be seen in video animations of the Coriolis effect. The reason wind moves clockwise in the North and not the other way has to do with the heating of air at the equator and air’s tendency to move towards low-pressure systems.
What the Coriolis Effect Means for the Ocean
Winds push the surface of the ocean’s water and are a major force in creating ocean currents. Ocean currents thus tend to reflect the wind patterns above them. As NOAA points out, ocean currents in the North such as the North Atlantic Gyre move clockwise while currents in the south move counterclockwise. The Coriolis effect also moves deeper water in what is known as the Ekman spiral.
The Coriolis Effect and the Ocean’s Ekman Spiral
As NOAA points out, the Coriolis effect is the force behind the Ekman spiral, responsible for the movement of water below the ocean’s surface. As the surface waters move, they drag the water molecules along below them. The Coriolis effect works on these lower layers of water as well. However, friction among the water molecules causes successively deeper layers of water to travel more slowly. Since deeper layers are being deflected at a slower pace a spiral occurs. The movement of the Ekman spiral stops at around 100 meters. Due to the spiral this deeper water tends to flow in the opposite direction of the surface water.
How the Coriolis Effect Impacts Marine Life
Plankton are the basis of many marine food webs and thus an important consideration when discussing marine life. As the Britannica Online Encyclopaedia points out in “Marine biota > plankton” these organisms tend to float with the oceans' currents. Many organisms depend on currents for dispersal in the larval stage. The Coriolis effect also influences upwelling, the bringing up of nutrient-rich cold waters to the surface. Many organisms rely on upwelling for nutrition. The Coriolis effect moves the very environment of marine organisms and thus shapes their lives in a profound way.
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