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Ocean Currents Ocean Currents An ocean current is a large amount of ocean water that moves in a particular unchanging direction. There are more than 20 major ocean currents. Currents can be warm or cold, depending on their origin. Two types of ocean currents 1. 2. surface currents (extend to an average depth of 200m). Thermohaline currents (occur deeper than 200m). Surface Currents 1. 2. 3. These are caused by: wind action the Earth’s spin (Coriolis Effect) shape of the continents Wind Action As air moves over the ocean’s surface, its energy is transferred by friction to the water molecules, causing the ocean water to move. Winds travel in a clockwise direction north of the equator and in a counter-clockwise direction south of the equator. Currents travel in the same direction Earth’s spin (Coriolis Effect) Earth spins from west to east (counterclockwise), as winds and currents move over this spinning body, their paths get re-directed depending on what side of the equator they are on. As a result, air currents flow in a clockwise pattern in the northern hemisphere and a counterclockwise pattern in the southern hemisphere. Shape of Continents Moving currents are forced to turn when they meet a solid surface. Deep Ocean Currents 1. 2. These are caused by: Temperature Salinity of the water Temperature 1. 2. 3. Water temperature varies with depth. There are three layers: the surface – warmest layer the thermocline – the water temperature may drop from 20ºC to 5ºC deep water – temperatures are close to the freezing point Temperature affects the density of ocean water. Cold water is more dense than warm water and tends to sink. Temperature differences in water may cause vertical convection currents where warmer water is rising and colder water is sinking. Theses masses of cold water are called density currents. Salinity of Water Density currents can also be caused by differences in salinity (amount of salt). Water with a high salinity is denser than water with a lower salinity. Local Currents Local ocean currents include: i) Labrador current (cold) ii) Gulf Stream (warm) Newfoundland and Labrador has a cold ocean current flowing down from the north (the Labrador current) and a warm ocean current flowing up from the south (the Gulf Stream). The mixing of these two currents generates heavy fog for our coastline and also makes an ideal location for nutrients Answer the following… 1. 2. 3. 4. What is a current? Describe and illustrate a convection current. Explain the importance of currents to the survival of aquatic organisms. Where are some of the most important fishing areas in our oceans? What causes these areas to generate such large numbers of fish?