Page 223 - NS-2 Textbook

218 NAUTICAL SCIENCES

shore or breakers lmtil you have gotten past the current. Pole, the polar 110rtheasterlies blow mainly from the north-
In other words, you should try to swim across the cur- east, causing surface current nlovement toward the west
rent, getting help from the rip, and using just enough (see the global winds diagram).
strength to avoid being pulled out to deep water beyond The combined effect of these winds is to create broad
the breaker line. By swimming across the current, you circular currents in the ocean basins in both the Northern
should be able to quickly get out of the main pull of the and Southern Hemispheres. The movements in the
rip and swim back to shore. You must not panic or strug- Southern Hemisphere are opposite from those in the
gle and overexert yourself. Northern Hemisphere because of the Coriolis effect.
These circular systems of currents are called gyres. (Keep
in mind that winds are named by the direction from
OCEAN CURRENTS AND GYRES
which they are blowing, while cmrents are described in
The study of ocean currents can be complex. Like every- terms of the direction in which they are flowing.)
thing else in oceanography, ne"v discoveries about the While these major currents are well defined; they
movements of ocean 'vater are being made all the time. continuously mingle with other currents, especially in
The effect that ocean currents have on people, the food the subpolar regions. Also, there is a constant exchange
cycle, and the weather of the world is profolmd. We can of Atlantic Ocean water with the Mediterranean Sea
only introduce this subject here and hope that some stu- through the Strait of Gibraltar. This is due to the differ-
dents will want to explore this fascinating area of ence in salinity of these two bodies of water, which
oceanography more on their O'wn. causes lighter Atlantic water to flow into the Mediter-
The movements of the atmosphere (winds) and ranean basin, while the heavier, saltier water flows out
oceans (currents) are linked to each other. A significant beneath it.
factor in these movements is the rotation of the planet on The Gulf Stream. The Gulf Stream is the most impor-
its polar axis. Earth/s rotation, or spin, creates an invisi- tant cmrent affecting the United States and its entire At-
ble force called the CarioUs effect, or CarioUs force. This lantic seaboard. The Gulf Stream system flows in a clock-
force deflects moving particles to the right (clockwise) in wise motion in the North Atlantic. In the center of this
the Northern Hemisphere, and to the left (counterclock- moving water mass is the legendary Sargasso Sea. Tbis is
wise) in the Southern Hemisphere. a vast area of floating plants, thought to be true natives
Two other important factors affect global movements of these waters, which float near the surface by means of
of wind and water. These are (1) wind acting on the air bladders. This is not a thick mass of seaweed that
water smface, and (2) the boundary effects of the conti- traps ships as is so often pictured in mystery stories of
nents. Because of the continents, no major ocean current the sea. On the average about 3 miles deep, this oval area
runs all the way around the world. is about 2,000 miles east and west by 1,000 miles north
The heating of water in the equatorial region causes and south. The blue waters of the Sargasso Sea form one
surface water there to rise and then to spread out and of the oceanic deserts, and the plant species that inhabit
flow" downhill" over the surface toward the poles. (The this region are adapted to this environment.
water level of the Sargasso Sea in the mid-Atlantic east of The North Equatorial Current carries warmer waters
Florida is actually about 3 feet higher than the water northwestward along the West Indies on the eastern rim
level along the west coast of the North Atlantic basin.) As of the Caribbean Sea. Part of the current breaks off and
it drifts toward the poles, this water cools and sinks, enters the Gulf of Mexico. The bulk of it rushes north-
pushing the water below it toward the equatorial re- ward to form the Gulf Stream that moves along the
gions. This kind of circular flow, caused by heat differ- Florida, Georgia, and Carolina coasts, and then begins to
ences within the water, is called c01lvection. The more im- spread out and turn eastward in the North Atlantic Drift.
portant factor affecting global water movements, though, TIle water flows northward at about 3 to 4 miles an hour.
is surface wind. Combined with the landmass place- The stream becomes wider and breaks off into meanders
ment, surface wind produces a different system. The re- (different streams) in the northern latitudes. As it goes
sulting surface water movements--ocean currents-are a along the Grand Banks of Newfoundland, it parallels
combination of these two flows. the southward-moving, cold Labrador Current. The
The prevailing winds in the Northern Hemisphere Labrador Current brings icebergs that have calved (bro-
blow from the northeast in the latitude belt from 0 to 30 ken away) from the western Greenland glaciers and
degrees. These are the trade Willds, which drive the ocean drifted into the North Atlantic shipping lanes. Here they
surface waters to the west. The prevailing winds in the meet the Gulf Stream's warm water and eventually melt.
belt from 30 to 60 degrees north blow from the southwest. In wintertime the warming effect of the Gulf Stream
These are the prevailillg westerlies, which drive the waters and North Atlantic Drift make the climate along the east-
back toward the east. From 60 degrees north to the North ern seaboard of the United States and Canada, Iceland,