Equator
Tropic of Cancer
Arctic Circle
Antarctic Circle
Tropic of Capricorn
P A C I F I C
O C E A N
A R C T I C
Caribbean
Gulf of
Mexico
Alaska
current
Pacific North
current
Equatorial countercurrent
Peru
current
California
current
breaking waves
seabed
sea swell
touching seabed
shallow waves
sea swell
3
50
3. Water on the Earth
2. OCEANS AND SEAS
Water in the oceans and seas is characterised by
temperature and
salinity.
For instance, water is
salty in bodies of water in hot climates because
evaporation
is a major factor. The term for water
at the polar caps is
glacier
because ice covers the
ocean in those areas for most of the year.
The movement of water in the oceans and seas
generates
waves
,
tides
, and
currents
.
2.1. Waves and tides
The surface of water forms small circular movements that break close to the coast
because of the shallow water.
On the coast, the sea seems to move in and out once or several times a day.
High
tide
is when the water reaches its highest point and
low tide
is when it reaches
its lowest point
.
2.2. Sea and ocean currents
❚
Hot currents
cause high temperatures and abundant rain on the coasts where
they circulate. One example of this is the Gulf Stream, which originates in the
Gulf of Mexico and flows along the coasts of Europe, allowing the area to be
populated and economic activity to grow.
❚
Cold currents
lower the temperatures and create deserts because the cold water
doesn’t evaporate and doesn’t cause rain
.
Did you know?
In Europe, the Baltic Sea has a
very low salinity, as it is located
very far north and there is
almost no evaporation. It also
receives a lot of fresh water
from rivers and glaciers. In
contrast, the Mediterranean
Sea, which is much further
south, in a much hotter region,
is much more salty.
Waves
are a result of the
rising and falling movement
of water because of the
pressure of
wind
on its surface
.
Tides
are the
periodic changes
in the level of the water in the oceans and seas
caused by the gravitational pull of the Sun and the Moon
.
Sea and ocean currents
are
bodies of water
that, like rivers, move and create
enormous circular patterns. They can be
hot
or
cold.
