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Alaska^ Cu

rrent^

North^ Pacific^ Curre

nt^

North Equatorial Current

Equatorial Countercurrent

South (^) Equ
atorial Countercurrent^
Peru
(^) Cu
rren
t
Hum
bo
ld
t^ C
ur
re
tn
Anta
rctic^ Circumpolar^ Current^
Fa
lkl
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Br
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Cu
rr
ent
Sou
th (^) E
qua
toria
l (^) Curr
ent
Equa
torial
Cou
nter
current
Nort
h (^) Equatoria
l^ C
ur
ren
t^
Can
ari
es^
Cu
rr
ne
(^) t
Gu
lf^ S
tream
Flo
rid
a^ C
urr
ent^ No
rth^ A
tlan
tic^ C
urre
nt^
La
arb
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r^ C
urrent
East
Green
land
Ben
gu
lae
(^) C
ur
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Ag
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la
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t
Mo
ns
oon
Dr
ift^
No
rth

• ea

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No

rth^ Equatorial (^) Cur
rent
Equatorial Countercurrent
North^
Equatoria
l Current
West^ A
ustr
alian
Cu
rre
nt
Eas
t^ Au
stra
lian
Cu
rren
t^
South^ Equatorial^
Current^
Equatorial
No
rth
Equatorial Current^
Ku
ros
hio
Cu
rre
nt
Oy
ash
io
Cu
rre
nt
Countercurrent^
Curr
ent^
Arctic Circle Arctic Circle
Tropic of Cancer Tropic of Cancer^
Tropic of^ Capricorn^
Antarctic^ Circle^ Antarctic^ Circle
Equator
Equator
30ºS 30ºS
60ºS 60ºS
30ºN 30ºN
60ºN
120ºE 150ºE
120ºW 90ºW 60ºW 30ºW 30ºE 60ºE 90ºE
150ºW
150ºW 120ºW
90ºW 60ºW 30ºW
0º 30ºE 60ºE 90ºE
120ºE 150ºE
NORTH
PACIFIC
GYRE
SOUTH
PACIFIC
GYRE
NORTH
ATLANTIC
GYRE
SOUTH
ATLANTIC
GYRE SOUTH
INDIAN
GYRE
40 Earth
WHAT CAUSES THE OCEAN CURRENTS?
Water in the oceans is constantly moving in huge,
slow circles called gyres. Prevailing (regular) winds
blowing across the oceans start currents near the
water’s surface, which may flow for thousands of
kilometres. Warm surface currents are heated by
the Sun. Some warm currents affect the climate
of the land that they flow past. For example,
the Gulf Stream keeps northern ports ice-free in
winter. There are also cold currents deep in the
oceans that flow from the poles and across the

. OCEAN FLOOR towards the Equator.

WHY IS THE SEA SALTY?

Sea water contains traces of minerals washed from

the land by rivers. These dissolved minerals are

mainly chloride and sodium, which together make

salt. Most oceans contain about one part salt for

every 35 parts water. The world’s saltiest sea, the

Dead Sea, contains around one part salt for every

five parts water, making it seven times saltier

than the rest of the oceans.

The Earth’s five oceans (the Pacific, Atlantic, Indian,

Southern, and Arctic) are constantly moving as tides rise and

fall and winds whip up. WAVES and help to drive ocean

currents. The oceans are major sources of minerals and food.

OCEAN LIFE 3

The oceans are home to a huge

variety of plant and animal life.

Microscopic plants drift in the

sunlit surface waters, forming the

basis of most of the ocean food

chain. They provide food for tiny

animal plankton, which are eaten

by fish, which, in turn, are eaten

by larger predators, such

as sharks).

Oceans

2 OCEAN SURFACE CURRENTS

The world’s oceans are interlinked in one continuous expanse of water.

Winds disturb this water, forming currents. On this map, warm surface

currents are shown in red. Cold currents are in blue.

4 SUNLIT ZONE

0–200 m (0–650 ft)

The oceans’ sunlit waters, just

below the surface, are home

to most plant and animal life,

including plankton, jellyfish,

flying fish, shoaling fish, tuna,

swordfish, and sharks.

4 TWILIGHT ZONE

200–2,000 m (650–6,500 ft)

Below the sunlit waters, the light

begins to fade until, by 1,000 m

(3,280 ft), it is completely dark.

Marine life includes lantern fish,

squid, prawns, and deep-diving

sperm whales.

4 ABYSSAL AND HADAL ZONES

2,000–10,000 m (6,500–33,000 ft)

The deepest parts of the ocean

are near freezing and pitch black.

Marine life includes gulper eels,

anglerfish, and rattail fish.

oceans