Miss Nelson

SCIENCE ~ CHAPTER 9

CLIMATE

Currents and Climate

SECTION 2

Have you ever heard a story about someone finding a message in a bottle that was thrown into the

ocean?

How did the bottle travel all the way to them?

ANTICIPATORY SET

S 6.4.d –Students know that convection currents distribute heat in the atmosphere and oceans

S 6.4.e –Students know differences in pressure, heat, air movement, and humidity result in change in weather

STANDARDS

What causes surface currents and deep currents?

What effects do they have?

THE BIG IDEA

El Niño –A climate that occurs every two to seven years in the Pacific Ocean, during which winds shift and push warm water toward South America

La Niña – A climate in the eastern Pacific Ocean in which surface waters are colder than normal

Salinity – The total amount of dissolved salts in water

Upwelling – The movement of cold water upward from the deep ocean that is caused by wind

Coriolis effect – The effect of Earth’s rotation on the direction of winds and currents

KEY TERMS

Read Currents and Climate on page 356 of your textbook

CURRENTS AND CLIMATE

Surface currents (which affect water to a depth of several hundred meters) are driven mainly by winds

SURFACE CURRENTS

Most of the currents flow east or west, and then double back to complete a circle

View Figure 8 on pages 457 of your textbook

SURFACE CURRENTS

Winds are caused by differences in air pressure

Differences in air pressure are the result of the unequal heating of the atmosphere by the sun

The sun’s radiation (of heat) is the ultimate source of energy that powers global winds and surface currents in the ocean

SURFACE CURRENTS

Global winds are not the only factors that influence surface currents

Continents block and redirect the flow of currents

Coriolis effect also influences surface currentsCauses global winds to curve as a result of Earth’s rotation

CORIOLIS EFFECT

A surface current warms or cools the air above it, influencing the climate of the land near the coast

EFFECTS ON CLIMATE

Warm-water currentsWinds pick up

moisture as they blow across

Cold-water currentsCool the air

above themCold air holds

less moisture – these currents tend to bring cool, dry weather to lands in their path

EFFECTS ON CLIMATE

Read Surface Currents on pages 357 – 358 of your textbook

SURFACE CURRENTS

El Niño and La Niña are short-term changes in the tropical Pacific Ocean cause by changes in ocean surface currents and prevailing winds

El Niño is a warm-water event that disrupts the cold ocean currents along the western coast of South America Effects weather patterns around the world

La Niña is the opposite – when surface waters in the Pacific are colder than normal Brings colder than normal winters and greater

precipitation Causes hurricane activity in the western Atlantic

EL NIÑO AND LA NIÑA

Read El Niño and La Niña on page 359 of your textbook

EL NIÑO AND LA NIÑA

Deep currents are caused by differences in the density of ocean water

DEEP CURRENTS

The density of ocean water depends on its temperature and its salinity

OCEAN WATER DENSITY

View Figure 11 on page 360 of your textbook

OCEAN WATER DENSITY

Deep currents move and mix water around the world

They carry water from the poles toward the equator

A GLOBAL CONVEYER BELT

Deep currents flow SLOWLY

May take as long as 1,000 years to flow from the pole to the equator and back again

A GLOBAL CONVEYER BELT

Read Deep Currents on page 360 of your textbook

DEEP CURRENTS

Upwelling brings up tiny ocean organisms, minerals, and other nutrients from the deeper layers of the water

UPWELLING

In most parts of the ocean surface waters do not usually mix with deep ocean waters

Mixing sometimes occurs as winds blow away the warm surface water and cold water rises up to replace it

Without this motion the surface waters of the open ocean would be very scarce in nutrients

UPWELLING

Upwelling occurs in the Pacific Ocean off the west coasts of North and South America

The arrival of El Niño prevents upwelling from occurring

Without the nutrients brought by upwelling, fish die or go elsewhere to find food

UPWELLING

Read Upwelling on page 361 of your textbook

UPWELLING

Surface currents are mainly driven by what?

What causes deep currents?

CHECK FOR UNDERSTANDING

Surface currents are mainly driven by what?Surface currents are driven mainly by winds.

What causes deep currents?Deep currents are caused by differences in the density of ocean water.

CHECK FOR UNDERSTANDING

Complete the Modeling, Guided Practice, and Independent Practice

Sections of your Climate 9-2 Worksheet.

MODELING / GUIDED / INDEPENDENT