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Ocean Circulation, Waves and Tides. Ocean water is in constant motion powered by many different forces. Wind generate surface currents and waves can impact upwelling. . Ocean currents are masses of ocean water that flow from one place to another. They can be on the surface or deep below.

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Presentation Transcript
slide2

Ocean water is in constant motion powered by many different forces. Wind generate surface currents and waves can impact upwelling.

slide3

Ocean currents are masses of ocean water that flow from one place to another. They can be on the surface or deep below.

slide4

SurfaceCurrents develop from friction between the ocean and the wind that blows across its surface. Some are small and some are large and cover much of the horizontal movements of surface waters that are closely related to the circulation pattern of the atmosphere.

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Gyres are huge circular-moving current systems in the oceans. There are 5 main gyres in the world.

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Beside the wind there are other factors that affect surface currents. The Coriolis effect is the deflection of the currents based on the Earth’s rotation. Currents are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

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Open Ocean Currents and Climate

Ocean currents have an important effect on climates. When currents from low-latitude regions move into higher latitudes, they transfer heat from warmer to cooler areas on Earth.

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An example is the Gulf Stream off the coast of the Southeastern U.S. brings warm water from the equator up to the North Atlantic Current which allows for Great Britain and much of Western Europe to be warmer during the winter than one would expect at that latitude.

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The opposite affect happens with cold water currents. As cold water currents travel toward the equator, they help moderated the warm temperatures of adjacent land areas. An example is the California Current.

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The ocean currents transport 25% of the Earth’s heat from the equator to the poles where the global winds transport the other 75%.

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Upwelling is the rising of cold water from deeper layers to replace wind-blow warmer surface water. Coastal upwelling takes place along the coast California, the west coast of South America and the west coast of Africa. As the wind blows toward the equator parallel to these coasts, the Coriolis effect causes surface water to move away from the shore clearing the way for the upwelling to occur.

Areas of upwelling

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Deep-Ocean Circulation

Deep-ocean currents have a vertical component as well as a horizontal movement. DensityCurrents are vertical currents of ocean water resulting from differences in density.

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An increase in sea-water density can be caused by a decrease in temperature or an increase in salinity. Most water involved in deep-ocean density currents begins in high latitudes at the surface. Surface water becomes cold, and its salinity increases as the sea ice forms. When the water becomes dense enough it sinks initiating the deep-ocean density currents. Density currents can also result from increased salinity due to evaporation.

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A simple model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean through the Indian and Pacific oceans and back again.

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In this model warm water in the ocean’s upper layers travels toward the poles. When the water reaches the poles it cools and salinity increases causing the water to sink and start moving toward the equator. When the cold dense water reaches the equator upwelling occurs completing the cycle.

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The conveyor belt moves around the globe influencing global climate by converting warm water to cold water and releasing heat into the atmosphere.

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Waves and Tides

Ocean waves are energy traveling along the boundary between ocean and atmosphere created by wind. Waves can travel for thousands of miles when created by the winds of storms.

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The height, length, and period that are eventually achieved by a wave depend on three factors: 1) wind speed; 2) length of time the wind has blown; 3) and fetch, which is the distance the wind has traveled over open water.

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Waves travel in a circular, rolling motion this allow energy to move forward through the water while the individual water particles that transmit the wave move around in a circle.

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Ocean tides result from differences in the gravitational attraction exerted upon different parts of the Earth’s surface by the Moon, and to a lesser extent, by the Sun.

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Newton identified in the late 1600’s that the gravitational pull of the Moon is the major cause of tides. The gravitational pull of the Moon is strongest on the side of the Earth nearest the Moon. As a result the ocean on the side of the Earth facing the moon bulges slightly, causing a high tide within the area of the bulge.

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There is also a high tide on the opposite side of the Moon because of the outward force generated by the Earth’s rotation. So there is always two high tides and two low tides somewhere on the planets.