Ocean Currents p. 36 Ocean waters are constantly on the move. How they move influences climate and living conditions for plants and animals, even on land. Currents flow in patterns affected by: 1. Solar Heating 2. Winds 3. Gravity 4. Coriolis

Types of Ocean Currents: 1. Surface Currents--Surface Circulation These waters make up about 10% of all the water in the ocean. These waters are the upper 400 meters of the ocean. 2. Deep Water Currents--Thermohaline Circulation These waters make up the other 90% of the ocean Deep waters are "formed" where the air temperatures are cold and where the salinity of the surface waters are relatively high. The combinations of salinity and cold temperatures make the water denser and cause it to sink to the bottom, causing a system of slow, deep water currents. In order for sea level to remain constant, if water sinks in one area, it must rise somewhere else. These areas where deep water rises to the surface are called areas of upwelling.

1. Solar Heating Solar heating causes water to expand. Near the equator the water is about 8 centimeters higher than in middle latitudes. This cause a very slight slope and water wants to flow down the slope.

Differential Solar Heating

2. Wind Winds blowing on the surface of the ocean push the water, creating currents. Friction occurs between the wind and the water's surface. A wind blowing across the ocean will cause the surface waters to flow at about 2% of the wind speed. Water will pile up in the direction the wind is blowing, and currents will travels until they strike an object (continent).

Trade Winds Ground-level winds that flow toward the equator and are deflected by the rotation of the Earth. This deflection is the Coriolis Effect.

Prevailing Westerlies Winds that occur between 30 and 60 degrees latitude. The air moves towards the poles and appears to curve to the east. Winds originate in the west. These winds are responsible for many of the weather movements across the US and Canada

Air moving from polar areas to tropics (wind) sets surface ocean water in motion Coriolis effect and continents affect surface current directions Equator Hadley cell H L H L L Surface flow

3. Gravity Gravity will tend to pull the water down the "hill" or pile water against the pressure gradient.

4. Coriolis Effect This effect is caused by the rotation of the Earth. Winds blow at an angle to the equator. Winds in the northern hemisphere blow to the right and winds in the southern hemisphere blow to the left.

Coriolis continued… Large mounds of water and the flow around them are called Gyres. They produce large circular currents in all the ocean basins.

Great Ocean Conveyor Belt Has enormous effects on:  World climate (heat transfer)  Fishing industry (upwelling areas are great fishing grounds)

The North Atlantic Gyre is separated into four distinct currents: The North Equatorial Current, the Gulf Stream, the North Atlantic Current, and the Canary Current.

Clockwise in Northern Hemisphere Anti-clockwise in Southern Hemisphere

Near surface warm currents are drawn in red. Blue depicts the deep cold currents. This system is continuously moving water from the surface to deep within the oceans and back to the top of the ocean. One complete circuit of this flow of sea water is estimated to take about 1,000 years.

Animated sequence: Q&NR=1

Ocean "conveyor belt” surface waters sink, enter deep water circulation, then resurface after slowly flowing through the deep ocean.

Connects all the world’s oceans!

Kv4SM

Cold, salty, dense water sinks under warmer, fresher water. The sinking of cold water at the poles and its replacement by warmer water from the equator creates a current. This is called a thermohaline circulation because it is based on temperature and water density due to salt content. thermo = temperature haline = salt Image: national academy of sciences

The Great Ocean Conveyor Belt Red = warm surface water Blue = cold salty deep water

A Polar View of the Global Ocean Conveyor Belt

Warm water carried north away from the Equator provides Europe with mild winters. Satellite image showing water temperatures along the eastern U.S. Images: