OCEAN CURRENTS AND CLIMATE. Ocean Currents and Climate There are two types of Ocean Currents: 1. Surface Currents are driven by surface wind circulation.

OCEAN CURRENTS AND CLIMATE

Ocean Currents and Climate There are two types of Ocean Currents:1. Surface Currents are driven by surface

wind circulation. These waters make up about 10% of all the water in the ocean. These waters are the upper 200 meters of the ocean.

2. Deep Water Currents are driven by Thermohaline Circulation- • Makes up the other 90% of the ocean. • Moves around the ocean basins by density-driven forces and gravity. The density difference is a function of different temperature and salinity.

•These deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.

Ocean Currents are influenced by two types of forces:Primary Forces start the water moving

a. solar heatb. winds

c. gravity d. Coriolis Effect

Primary Force: solar heat

Causes thermal expansion of water about 8 centimeters higher at the equator

Atmospheric heating sets the winds in motion to the poles and the Coriolis Force adds a “twist” to its motion.

Primary Force: Winds

Primary Force: gravityElevated water at the equator begins to “flow poleward” due to gravity.

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

Primary Force: CoriolisThe curvature of motion due toEarth’s rotation.Curvature is to right in the Northern Hemisphere, to left in the SouthernHemisphere.

Atlantic Gyre– composed of the:A. Gulf StreamB.North Atlantic DriftC. Canary CurrentD.North Equatorial current

Why doesn't the water spintowards the center of the ocean?

Why does it flow around the hillin this circular motion?

Answer: Ekman Transport

Ekman Transport –

The friction from underlying water slows down the upper current and the Coriolis Forces gives it a twist (to the right in the Northern Hemisphere).

A wind blowing for 10 hours 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.

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

•But the Coriolos Force intervenes and cause the water to move to the right (in the northern hemisphere) around the mound of water.

The net movement of water (averaged over the entire upper 330 meters of the ocean) is 90º to the right of the wind direction (in the northern hemisphere).

When the water is pushed to the right it forms the hill we described above. So, when water is pushed along by the wind it wants to be turned to the right by the Coriolis force (in the northern hemisphere) but it must fight against gravity (trying to move up the hill of water formed by Ekman transport).

A balance is met between the Coriolis and the gravity (pressure gradient force).This balance produces a balanced flow

called a Geostrophic current.

Geostrophic Current

Eastern and Western Boundary Currents

Boundary Currents are the major geostrophic currents around the gyre.

The Gulf Stream is an example of a

Western Boundary Current.

The Canary Current is an example of an Eastern Boundary

Current.

Major Gyres of the world Note the location of the Eastern and Western

Boundary Currents.

Western Boundary Currents originate in low latitudes and move to high latitudes.

They are warm, shallow, fast-moving currents

Eastern Boundary Currents originate in high latitudes and move to low latitudes.

They are cold, deep, slow-moving currents.

Upwelling along the coast -caused by Ekman transport of waters (waters move to the right of the wind). The waters moved offshore are replaced by waters from below. This brings cold, nutrient-rich waters to the surface. It has a fertilizing effect.

Most of the world’s great fisheries are found in areas of upwelling.

http://www.youtube.com/watch?v=XV90dy0ns1U&NR=1

Upwelling demonstration

Downwelling –caused by Ekman transport onshore (movement of water to the right of the wind direction).It pusheswater to shore andthen it sinks.

Global Conveyor System

Global Conveyor SystemThermohaline circulation distributes heat from tropics to poles

Deep ocean cold currents upwell, bringing nutrients to the surface.

Speed of flow is thought to have major impacts on global climate systems