Page 298 - (DK) The Ultimate Visual Dictionary 2nd Ed.

GEOLOGY, GEOGRAPHY, AND METEOROLOGY
Oceans and seas SURFACE CURRENTS

GREENWICH
180°
160°
MERIDIAN
120°
80°
OCEANS AND SEAS COVER ABOUT 70 PERCENT of the Earth’s 40° 0°
surface and account for about 97 percent of its total
water. These oceans and seas play a crucial role in East Greenlan d Curr ent
regulating temperature variations and
determining climate. Their waters absorb Al a s k a Cu r r e n t L a bra d or Current
heat from the Sun, especially in tropical North Pa ci fi c Current North Atlantic Current
regions, and the surface currents distribute
it around the Earth, warming overlying Flor ida Cu rr ent
air masses and neighboring land in PA C IFIC Gulf Stream Ca n a ri es Cu rre nt
NO RTH
GYRE NO RTH
winter and cooling them in summer. ATL ANTIC
GYRE
The oceans are never still. Differences North Equatoria l Cu rren t Nor th E quatoria l Curre nt
in temperature and salinity drive
E qu a t o ri al C ou n t er c ur re nt
deep current systems, while surface S o u th E q u a t o r i a l Cu r r e n t Equ a to ri al
Countercurr en t
currents are generated by winds S o ut h E qu a t o ri a l C urr e n t
blowing over the oceans. All currents
are deflected—to the right in the Per u C u r r e nt
Northern Hemisphere, to the left in Br a z il Cu rr en t Ben g u el a Cu r r ent
the Southern Hemisphere—as a result ATLANTI C
SOUTH
of the Earth’s rotation. This deflective GYRE
factor is known as the Coriolis force. SOUTH Hum b old t Cur r ent
PA CIFIC
A current that begins on the surface is GYRE Falkla nd Current
immediately deflected. This current in
turn generates a current in the layer of water
beneath, which is also deflected. As the movement An t a r ct i c C ir c um p o l ar C u rr en t
is transmitted downward, the deflections form an
Ekman spiral. The waters of the oceans and seas are
also moved by the constant ebb and flow of tides. These
are caused by the gravitational pull of the Moon and Sun. 80° 40° 0°
120°
The highest tides (Spring tides) occur at full and new Moon; 180° 160° GREENWICH
MERIDIAN
the lowest tides (neap tides) occur at first and last quarter.
OFFSHORE CURRENTS
SALT CONTENT OF SEAWATER Surface Wind drives Cold-water Surface Pack-ice formation
ocean water along upwelling ocean increases water
Others current coast replaces warm current salinity and density
Potassium 1.9% surface water
1.1%
Calcium
Magnesium 1.2%
3.7%
Sulfate
7.6%
Sodium
30.2%

Chloride
54.3%

Continental slope Cold, dense Continental
water sinks slope
COLD-WATER UPWELLING
(SOUTHERN HEMISPHERE) POLAR BOTTOM WATER

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