THE WORLD’S OCEANS51Ocean circulation The circulation of the
ocean partly controls climate, because warm
or cold air masses move with ocean currents.
The Gulf Stream takes warm, salty water from
the Caribbean to the Nordic seas and brings
mild weather to northern Europe. Without
the Gulf Stream, winters in Lisbon, Portugal,
would be more like winters in New York,
which is a similar distance from the North
Pole. Around Iceland, the Gulf Stream’s salty
water gets cold and heavy and sinks down,
sucking more warm water from farther south
to replace it. That deep cold water flows from
the Arctic to the Southern Ocean, where it
meets an even deeper cold current flowing
eastward around Antarctica. Similar processes
take place in the Indian and Pacific oceans.
Continental margins The land does
not stop when it meets the ocean. The
continental shelf extends out for about
650 ft (200 m) then slopes sharply
down to the ocean floor. Although large
areas of the floor, or abyssal plain, are
flat, it is not featureless. There are deep
canyons and trenches, volcanic sea
mounts, and spreading ocean ridges.
EARTHLife at the bottom of the
deep ocean is hard.
The weight of water
above is so heavy it
can crush organisms
that use lungs to
breathe. It is dark
because light cannot
reach very far, which also
makes it cold. Animals that live here
need special adaptations to help
them survive.DEEP, BLUE SEA
Wa v e s Waves are caused by winds blowing over
the ocean. These produce smooth, large waves
called swells. As they get closer to shore
they begin to pile up. The depth
between the wave and the
seafloor becomes shallower,
causing the wave to break
into a foamy crest that
crashes onto the beach.Salt water As everyone knows,
seawater tastes salty, and will make you
thirsty if you try to drink it. Not only is
common salt (sodium chloride) found
in seawater, but many other minerals
as well. There is even a little dissolved
gold. Scientists estimate there could be
as much as 50 million billion tons
(tonnes) of dissolved salts in the sea.
If this were spread on the land it would
measure 500 ft (150 m) deep.Pacific
OceanAntarcticaN. AmericaAfricaAustraliaBeach
Submarine canyon Sea mount Abyssal plain
Midocean ridgeContinental slopeBreaking
wave crashes
onto beach.
Waves pile up as
they near land.Warm surface currentsCold deep currentsThe Gulf Stream BUOYED UP Some “seas” are
actually salty lakes.The Dead Sea is so salty
you can float without making any effort.Continental shelf
Continental riseIndian
OceanAtlantic
OceanPacific
OceanSouthern OceanArctic OceanS. AmericaNorth SeaMediterranean SeaCaribbean SeaOcean swell