Ocean Currents

The water in the ocean is constantly moving The water in the ocean is constantly moving Broad bands of ocean water that flow in one direction and connect one place to another are known as currents Broad bands of ocean water that flow in one direction and connect one place to another are known as currents There are two main types of currents: There are two main types of currents: a) horizontal and a) horizontal and b) vertical b) vertical

A) Horizontal Currents Also known as surface currents Also known as surface currents Flow in the top 100 to 200m of water Flow in the top 100 to 200m of water Primarily driven by winds Primarily driven by winds Three factors influence the direction of winds and surface currents: Three factors influence the direction of winds and surface currents: –1.Uneven heating of the atmosphere –2.Rotation of the earth –3.continents

1. Uneven Heating of the Atmosphere All winds begin as a result of uneven heating of the atmosphere All winds begin as a result of uneven heating of the atmosphere Warm air expands and rises, producing an area of low pressure Warm air expands and rises, producing an area of low pressure Cooler air will move into the area (higher pressure) Cooler air will move into the area (higher pressure) These moving masses of air create winds These moving masses of air create winds

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2. Rotation of the Earth This produces a bending of moving currents called the Coriolis effect This produces a bending of moving currents called the Coriolis effect Wind and water current flow over the Earth’s surface, and the planet is turning beneath them from west to east Wind and water current flow over the Earth’s surface, and the planet is turning beneath them from west to east This motion causes current in the Northern hemisphere to turn to their right relative to the Earth’s surface This motion causes current in the Northern hemisphere to turn to their right relative to the Earth’s surface

Currents in the southern hemisphere turn to their left Currents in the southern hemisphere turn to their left The overall result is that winds along the equator blow from the east The overall result is that winds along the equator blow from the east these are called trade winds these are called trade winds Trade winds push ocean currents near the equator to the west (so from east to west) Trade winds push ocean currents near the equator to the west (so from east to west) Near the polar regions, westerly winds drive currents from west to east Near the polar regions, westerly winds drive currents from west to east

3. Continents Moving ocean currents are forced to turn when they meet a continent Moving ocean currents are forced to turn when they meet a continent Continents deflect east-west currents to either the north or south Continents deflect east-west currents to either the north or south

The combined influence of winds, the Coriolis effect, and the continents keeps ocean currents circulating clockwise in the northern hemisphere and counterclockwise in the southern hemisphere The combined influence of winds, the Coriolis effect, and the continents keeps ocean currents circulating clockwise in the northern hemisphere and counterclockwise in the southern hemisphere

Gyres

B) Vertical Currents Flow beneath the surface waters and result in either the downward or upward movement of water Flow beneath the surface waters and result in either the downward or upward movement of water Density currents are downward moving currents and are caused by differences in density and salinity Density currents are downward moving currents and are caused by differences in density and salinity Cold water is denser than warm water, and tends to sink Cold water is denser than warm water, and tends to sink In the oceans, sinking masses of cold water flow downward and move along the sea floor In the oceans, sinking masses of cold water flow downward and move along the sea floor

Saltier water is denser than less salty water, and will tend to sink Saltier water is denser than less salty water, and will tend to sink The sinking masses of saltier water flow downward and move along the sea floor The sinking masses of saltier water flow downward and move along the sea floor Both evaporation and freezing of water will cause increases in salinity, and lead to the formation of density currents Both evaporation and freezing of water will cause increases in salinity, and lead to the formation of density currents

Upwelling Occurs when the current flows from the sea floor up to the ocean surface Occurs when the current flows from the sea floor up to the ocean surface Most common along coastlines where strong winds blow offshore Most common along coastlines where strong winds blow offshore Winds will blow the surface water away from the land Winds will blow the surface water away from the land Cold, deep water then rises from below to replace the surface water that has been moved out to sea Cold, deep water then rises from below to replace the surface water that has been moved out to sea

Upwellings have an important effect on the ecology of the sea and on human fisheries Upwellings have an important effect on the ecology of the sea and on human fisheries Upwelling water contains a large amount of nutrients from the sea floor Upwelling water contains a large amount of nutrients from the sea floor Plants living near the surface will use these nutrients to grow Plants living near the surface will use these nutrients to grow Plants then attract fish to areas of upwelling Plants then attract fish to areas of upwelling

Major fishing industries are based on upwellings along the coast Major fishing industries are based on upwellings along the coast Fishing industries along the west coast of the US and Peru are based on the upwelling that occurs there Fishing industries along the west coast of the US and Peru are based on the upwelling that occurs there

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