Chapter 21 Section 1

Ocean Currents Objectives Describe how wind patterns, the rotation of the Earth, and continental barriers affect surface currents in the ocean Identify the major factor that determines the direction in which a surface current circulates Explain how differences in the density of ocean waters affect the flow of deep currents

Ocean Currents The water in the ocean moves in giant streams called currents Oceanographers study currents by examining the physical and chemical characteristics of ocean water They also identify currents by mapping the paths of debris that is dumped or washed overboard from ships Scientists place currents into two main categories, surface and deep currents

Ocean Currents Currents that move on or near the surface of the ocean, and are driven by winds are called surface currents These are controlled by three factors, winds, Earth’s rotation, and location of the continents Winds are caused by uneven heating of the atmosphere

Ocean Currents Global wind belts, such as trade winds and the westerlies are major factors affecting the flow of ocean surface waters Trade winds are located just north and south of the equator In the Northern Hemisphere they blow from the north east In the Southern Hemisphere they blow from the south east

Ocean Currents Continents are another major influence on surface currents They act as barriers to surface currents When surface currents flow against the continents the current is deflected and divided

Ocean Currents Global wind belts and ocean currents do not flow in straight lines, the follow a curve or circular pattern that is caused by Earth’s rotation The Coriolis Effect cause huge circles of moving water called gyres, to form

Ocean Currents Warm equatorial currents move in a western direction in the oceans Between these westward flowing currents lies a weaker, eastward flowing current called the Equatorial Countercurrent

Ocean Currents In the Southern Hemisphere the currents in gyres move counterclockwise In the most southerly region of the oceans constant westward winds produce the world’s largest current, the Antarctic Circumpolar Current also known as West Wind Drift No continents interrupt the movement of the current that completely circles Antarctica

Ocean Currents The Indian Ocean surface currents follow two patterns, in the south they follow a circular counter clockwise gyre In the north they are governed by monsoons and change seasonally

Ocean Currents In the North Atlantic warm ocean water moves through the Caribbean Sea and the Gulf of Mexico and north along the east coast of North America in a swift long current called the Gulf Stream Further north the Labrador Current flows south and joins the Gulf Stream

Ocean Currents At the poles water cools and freezes making the water saltier and denser The denser water sinks and begins to flow toward the equator The journey of this cold dense water takes hundreds of years to complete

Ocean Currents The temperature of water near Antarctica is very cold and the water salinity is high This makes the water of Antarctica the densest and coldest water in the ocean This forms a deep current called Antarctic Bottom Water

Ocean Currents A strong current caused by an underwater landslide is a turbidity current This occurs along the continental shelf or the continental slope, and a large amount of sediment breaks loose The cloudy water gets denser than the surrounding water, moves beneath the clear, less dense water