BISL 04-Weather and Climate

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An

O

cean water moves as waves, tides, and currents. There are

two types of currents: surface and deep. The surface

currents, caused by the wind, are great rivers in the ocean.

They can be some 50 miles (80 km) wide. They have a profound

effect on the world climate because the water warms up near

the Equator, and currents transfer this heat to higher latitudes.

Deep currents are caused by differences in water density.

Ocean Currents

TIDES AND THE CORIOLIS EFFECT
The Coriolis effect, which influences
the direction of the winds, drives the
displacement of marine currents.

SUBPOLAR ARCTIC

CIRCULATING SYSTEM

For the last five decades,

these currents have been

shown to be undergoing

dramatic changes.

EKMAN SPIRAL

explains why the

surface currents and

deep currents are

opposite in direction.

DEEP CURRENTS

have a vital function of carrying

oxygen to deep water. This permits

life to exist in deep water.

THE FOUR SEASONS

OF A LAKE

Because of the physical

properties of water, lakes

and lagoons have a special

seasonal circulation that

ensures the survival of living

creatures.

GEOSTROPHIC BALANCE

The deflection caused by the Coriolis effect on

the currents is compensated for by pressure

gradients between cyclonic and anticyclonic

systems. This effect is called geostrophic balance.

Coriolis

force

Low pressure

Subpolar low pressure

Currents in the
Northern
Hemisphere travel
in a clockwise
direction.

In the Southern

Hemisphere, the

currents travel in a

counterclockwise

direction.

High pressure

Subtropical high-

pressure center

Pressure

gradient

Winds

22 SURFACE FACTORS WEATHER AND CLIMATE 23

THE INFLUENCE OF THE WINDS

HOW CURRENTS ARE FORMED

Wind and solar
energy produce
surface currents
in the water.

1. 
   

In the Southern

Hemisphere, coastal winds

push away the surface

water so that cold water

can ascend.

Warm surface

waters

Deep cold

water

Deep

layers

COAST

Subsurface

waters

occupy the space

left by the

motion of the

surface waters.

This slow ascent of deep

water is called a surge. This

motion is modified by the

Ekman spiral effect.

Wind energy is

transferred to the water

in friction layers. Thus,

the velocity of the

surface water increases

more than that of the

deep water.

The Coriolis effect

causes the direction of

the currentsto deviate.

The surface currents

travel in the opposite

direction of the deep

currents.

64° F (18 °C)

61° F (16 °C)

57° F (14 °C)

54° F (12 °C)

Near Greenland,

the North Atlantic

water sinks, and

the colder and

more salinewater

is pushed

southward.

Gulf

Stream

Summer

stratification

77 °

75 °

64 °

55 °

46 °

43 °

41 °

41 °

46 °

46 °

41 °

32 °

35 °

37 °

39 °

37 °

39 °

Epilimnion

Thermocline

Hypolimnion

Fahrenheit

Ocean conveyor belt

Warm Cold

Winter mixture

Spring mix

Autumn mixture

1

Warm surface water

from the Gulf Stream

replaces the cold water

that is sinking.

2

SUMMER

Stable summer temperatures

prevent vertical circulation in the

body of water of the lagoon.

AUTUMN

Temperature decrease and

temperature variations generate

a mixing of the surface and deep

waters.

WINTER

When the water reaches 39° F

(4° C), its density increases. That

is how strata of solid water on

the surface and liquid water

underneath are created.

SPRING

The characteristics of water once

again initiate vertical circulation in

the lake. Spring temperatures lead

to this circulation.

Warm current

Cold current

2.