Ocean Currents

What is a current? A large stream of moving water that flows through the ocean.

Surface Currents Controlled by three things: Global winds Coriolis Effect Position of continents Move in the upper few hundred meters of the water Warms or cools the air above it, influencing the climate of land near the coast.

1. Global Winds Different winds cause currents to flow in different directions Near the equator – winds blow ocean water east to west Closer to the poles – ocean water is blown west to east Merchant boats use winds to help them travel more quickly.

2. The Coriolis Effect Earth’s rotation causes wind and surface currents to move in curved paths Imagine trying to roll a ball straight across a turning merry-go-round… the spinning causes the path of the ball to curve. Northern Hemisphere, wind/currents clockwise Southern Hemisphere: move counterclockwise http://topex-www.jpl.nasa.gov/gallery/tiffs/videos/coriolis.mov

3. Continental Deflection If there were no continents, currents would move in uniform patterns BUT…as currents “bump into” continents, they change direction

Temperature All three factors – winds, Coriolis Effect, and continents – Work together to form a pattern of surface currents on Earth But the current is also affected by the temperature of the water in which it forms Warm water currents – start near equator Cold water currents – start near poles

Gulf Stream Powerful surface current in the Atlantic. 30km wide and 300m deep Carries a volume of water 100x greater than Mississippi River. 25x more water than all rivers in the world From the Gulf of Mexico to Caribbean Sea and up the north coast of the U.S.

Before much was known about ocean currents, sailors would stop their boats for the night only to wake up extremely confused when they found themselves miles away from where they stopped. The Gulf Stream is one current that presented these ancient mariners with many challenges. This especially powerful current is almost 1 mile (1.6) kilometers deep and can move up to 26 billion gallons of water a second. That's more than the flow of the Amazon River! The current has caused so many shipwrecks around Cape Hatteras, a piece of land that juts out sharply from the east coast of North Carolina, that the area is called the graveyard of the Atlantic.

Deep Currents Currents far below surface Not controlled by wind Caused by differences in density and salinity Lowering the temperature and increasing the salinity increases the density of water Where there is denser water – currents begin Move slower and may take as long as 1,000 yrs to make a round trip Carry cold water from the poles back to the equator along the ocean floor.

How Deep Currents form Warm surface currents flow toward poles, water cools, becomes denser and sinks (becoming deep currents) Then as water curves back away from poles, it rises – called upwelling

Upwelling The upward movement of cold water from the deep ocean. As wind blows away warm surface water, cold water rises (deep ocean currents) to replace it – it warms and becomes surface currents Brings tiny organisms, minerals, and other nutrients to surface to supply food for phytoplankton and zooplankton. Without it ocean would be scarce in nutrients and the food chain would suffer!

Deep Currents are crucial to the base of the world's food chain Deep Currents are crucial to the base of the world's food chain. As they transport water around the globe, they enrich carbon dioxide-poor, nutrient-depleted surface waters by carrying them through the ocean's deeper layers where those elements are abundant. The nutrients and carbon dioxide from the bottom layers that are distributed through the upper layers enable the growth of algae and seaweed that ultimately support all forms of life. They also help to regulate temperatures.

Before much was known about ocean currents, sailors would stop their boats for the night only to wake up extremely confused when they found themselves miles away from where they stopped. The Gulf Stream is one current that presented these ancient mariners with many challenges. This especially powerful current is almost 1 mile (1.6) kilometers deep and can move up to 26 billion gallons of water a second [source: Osher]. That's more than the flow of the Amazon River! [source: MSN Encarta]. The current has caused so many shipwrecks around Cape Hatteras, a piece of land that juts out sharply from the east coast of North Carolina, that the area is called the graveyard of the Atlantic. A well-known density-driven current occurs where the saltier Mediterranean Sea empties into the Atlantic Ocean. During World War II, submarines used this current to enter and leave the Mediterranean without even turning on their engines!