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What Two Things Keep Ocean Water Moving Constantly?

The movement of ocean waters is affected by a variety of factors, some major and some minor. The movement of ocean waters have a direct effect on habitats, weather patterns and the life cycles of plants and animals on Earth. The oceans cleanse themselves by movement and transport nutrients. Two main factors keep the oceans in a constant state of movement: primary forces, which get the water moving, and secondary forces, which keep the water moving. Both forces contribute to the vertical and horizontal movement of ocean water.

  1. Primary Forces -- Solar Heating

    • Thermal heating of the ocean's water causes it to expand or rise slightly. The thermal expansion that happens near the Earth's equator causes the water to rise up about 8 centimeters higher than in the mid latitudes. The result causes a slope, which directs the water in a downhill direction to colder regions.

    Primary Factors -- Density

    • Glacier melt and freezing temperatures cause water to sink in the upper latitudes because it becomes saltier and more dense. It moves south, forming a "conveyor belt" which loops around Antarctica, then continues on to the Pacific, Atlantic and Indian oceans, where it becomes warmed by the tropical waters. With the assistance of wind and the Earth's rotation, the current speeds up and returns to the temperate latitudes to start the cycle again.

    Primary Factors -- Wind

    • Wind is a primary force that starts water moving. Concentrated bands, or wind layers, called the Westerlies and the Trade Winds, blow across the top layer of the water's surface. Wind will transfer roughly 2 percent of its speed to the upper water layers over a 10-hour period. The friction from the top layer of water gets transferred to the lower, deeper levels, but it does not take up the same speed as the surface water.

    Secondary Forces -- Coriolis Effect

    • The Coriolis effect happens as a result of the Earth's rotation. The circulation of the air becomes deflected and rotates in a right spin in the Northern Hemisphere and flows in the opposite direction (left) in the Southern Hemisphere. This causes curved rotational paths, which affect the direction and behavior of the currents.

    Secondary Forces -- Gravity

    • When water presses against continents due the Coriolis effect (in either direction), it must overcome gravity by moving up a hill of water created by the Ekman transport (a combination of wind and the Coriolis effect). A balance in the gravity is formed between the Coriolis effect and the gravity pressure. The balance of the two forces creates a Geostrophic current.

    Secondary Forces -- Topography

    • The topography of the ocean basin, where the current flow remains fast and deep, cuts deep channels and trenches in the ocean floor. The location and physical profile of the channels, dictate the speed and volume of the currents. Trenches that have bottleneck characteristics, for instance, speed up at the choking point between submarine canyon walls. The largest and oldest currents have cut the oldest and deepest channels and trenches in the ocean floor.

    Tides

    • Although the tides do not directly affect the movement of large water currents, they do move vast amounts of water in the coastal regions throughout Earth. The pull of the moon and the downward gravitational force of the Earth, produce bulges (twice a day) in the equatorial regions of the Earth. The spin, or Coriolis effect, also determines the location of the highest tides. The sun influences the tides, but not as strongly as the moon's gravitational force.

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