Ocean Currents (see “ships in storm” video

 By some estimates, as many as cargo containers are lost, during storms, every year.

 Most of these containers end up on the bottom of the ocean, but sometimes they break open and spill their contents into the ocean.

 In 1992, a container with a shipment of rubber ducks (and other bathtub toys) fell into the Pacific Ocean and have been being tracked ever since by Dr, Charles Ebbesmeyer.

The map below shows their journey so far.

 Neat story, but so what????  The rubber ducks is an illustration of how water moves through the world’s ocean transferring ducks, but also transferring energy. Look at the map below.  Neat story, but so what????  The rubber ducks is an illustration of how water moves through the world’s ocean transferring ducks, but also transferring energy. Look at the map below.

(watch “yellow rubber ducks” movie)

Why is Ocean Circulation Important?  Transport ~ 20% of latitudinal heat  Equator to poles  Transport nutrients and organisms  Influences weather and climate  Influences commerce

Convection cell model Non-rotating Earth

Add rotation and add landmasses unequal heating and cooling of the Earth

Physical properties of the atmosphere: Density Warm, low density air rises Cool, high density air sinks Creates circular- moving loop of air (convection cell)

The Coriolis effect on Earth As Earth rotates, different latitudes travel at different speeds The change in speed with latitude causes the Coriolis effect

A)Idealized winds generated by pressure gradient and Coriolis Force. B)Actual wind patterns owing to land mass distribution..

Surface Currents The upper 400 meters of the ocean (10%). Deep Water Currents Thermal currents (90%) Ocean Currents

Surface Currents Forces 1.Solar Heating (temp, density) 2.Winds 3.Coriolis

Wind-driven surface currents -We are largely impacted by the “Kuroshio” current (watch “Tsunami debris” video)

Sailors have know about ocean currents for centuries Sailors have know that “ rivers ” flow in the seas since ancient times. They used them to shorten voyages, or were delayed by trying to stem them. If navigators do not correct to deflection by currents, they may be far away from where they think they are and meet disaster. Sailors have know that “ rivers ” flow in the seas since ancient times. They used them to shorten voyages, or were delayed by trying to stem them. If navigators do not correct to deflection by currents, they may be far away from where they think they are and meet disaster.

Matthew Fontaine Maury The first systematic study of currents was done by Maury based on logbooks in the US Navy ’ s Depot of Charts and Instruments. His charts and “ Physical Geography of the Sea ” assisted navigators worldwide. The first systematic study of currents was done by Maury based on logbooks in the US Navy ’ s Depot of Charts and Instruments. His charts and “ Physical Geography of the Sea ” assisted navigators worldwide.

Winds and surface water  Wind blowing over the ocean can move it due to frictional drag.  Waves create necessary roughness for wind to couple with water.  One “ rule of thumb ” holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)  Wind blowing over the ocean can move it due to frictional drag.  Waves create necessary roughness for wind to couple with water.  One “ rule of thumb ” holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)

Top-down drag  Wind acts only on the surface water layer.  This layer will also drag the underlying water, but with less force.  Consequently, there is a diminution of speed downward.  Direction of movement is also influenced by the Coriolis Effect and Ekman spiral  Wind acts only on the surface water layer.  This layer will also drag the underlying water, but with less force.  Consequently, there is a diminution of speed downward.  Direction of movement is also influenced by the Coriolis Effect and Ekman spiral

Ekman spiral Ekman spiral describes the speed and direction of flow of surface waters at various depths  Factors:  Wind  Coriolis effect Ekman spiral describes the speed and direction of flow of surface waters at various depths  Factors:  Wind  Coriolis effect

Ekman transport Ekman transport is the overall water movement due to Ekman spiral

Ekman Transport

Water flow in the Northern hemisphere- 90 o to the right of the wind direction Depth is important as the Ekman spiral only goes so deep (150 m)

Currents in the “ Real ” Ocean Currents rarely behave exactly as predicted by these theoretical explanations due to factors such as  Depth — shallow water does not permit full development of the Ekman spiral  Density — deeper currents moving in different directions influence the overlying surface movement Currents rarely behave exactly as predicted by these theoretical explanations due to factors such as  Depth — shallow water does not permit full development of the Ekman spiral  Density — deeper currents moving in different directions influence the overlying surface movement

Surface Currents Surface currents generally mirror average planetary atmospheric circulation patterns (watch “modeling dynamic surface ocean currents” video)

Gyres are large circular-moving loops of water Five main gyres (one in each ocean basin): North Pacific South Pacific North Atlantic South Atlantic Indian Generally 4 currents in each gyre Centered about 30 o north or south latitude Current Gyres

5 Main Gyres

Pacific Ocean surface currents (watch “great pacific garbage patch” video)

Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity. (watch “Ocean Odyssey: Density currents” video)

Surface and Deep-Sea Current Interactions Unifying concept: “ Global Ocean Conveyor Belt ”

The Air Above Ocean Currents  Water brings with it the characteristics it possesses.  What do we mean by that?  Warm currents make the air above them warmer,while cool currents cool the air above them  Water brings with it the characteristics it possesses.  What do we mean by that?  Warm currents make the air above them warmer,while cool currents cool the air above them

What is the Gulf Stream?  Ask Ben Franklin  A strong ocean current that moves warm water Eastward across the Atlantic from the Eastern U.S. to Europe ( see gulf stream video)  Ask Ben Franklin  A strong ocean current that moves warm water Eastward across the Atlantic from the Eastern U.S. to Europe ( see gulf stream video)

When Currents Collide  What happens when a cool currents (e.g. The Labrador Current) comes close to (or collides with) a warm current (e.g. the Gulf Stream)?

Answer: Fog

The Foggiest Place in the World -Grand Banks, where the Labrador Current and the Gulf Stream collide, is the foggiest place in the world.

Review Questions  Why is ocean circulation important?  What percentage of the oceans currents are on the surface?  Why is it important that cargo ships know about ocean currents?  What is a gyre? What are the 5 main gyres?  How do ocean currents affect the air above them?  Why is ocean circulation important?  What percentage of the oceans currents are on the surface?  Why is it important that cargo ships know about ocean currents?  What is a gyre? What are the 5 main gyres?  How do ocean currents affect the air above them?