Page 219 - NS-2 Textbook

214 NAUTICAL SCIENCES

The hydrologic cycle is the continuous movement of moisture by evaporation into the atmosphere, where it condenses and falls back to Earth
as precipitation and then returns to the sea. During its journey over Earth's surface, the water dissolves minerals and carries them either sus-
pended or in solution back to the ocean. This explains how the oceans became salty.

Only magnesium and bromille are presently taken from "record"). Most Navy combatants have an XBT to take
the ocean water commercially. TIus is because the supply readings for continuous lllOlutoring of the ocean for lUl-
of most of the other millerals is still plentiful from land dersea vvarfare.
milling sites, and it would cost too much to extract them Ocean water samples can be taken in Nmlsell bottles,
from semvater. Much of the magnesiunl used in the man- named for a Norwegian oceanographer, Fridtjof Nansen.
ufacture of lightweight alloys for airplanes and satellites The Nansen bottle is a llletal cylinder ,vith automatic
now comes from the sea, however. TIle bromine is used closing valves on each end. These valves are linked by
in the manufacture of antiknock gasoline and other levers so they work together. The bottles are attached up-
chemicals. Research is constantly being done to try to de- side dmNn on a long ,viTe. During lmvering, 'vater flows
velop profitable methods of extracting dissolved miner- straight through the bottle until it reaches the desired
als from the sea. TI,is is an area of oceanography and depth. At sampling depth, a weight called a messenger is
metallurgy (the extraction of metals from are or seawa- sent down the ,viTe, releasing the first bottle, -which over-
ter) that will undoubtedly expand as continental mineral till'ns, its valves closing to seClU'e the sample, Another
resources are used up. messenger weight, formerly resting on that bottle, then
slides down to repeat a similar action on the next bottle
belmv.
WATER TEMPERATURE
As the Nansen bottles capture the water at each de-
Upper ocean water temperature varies from about 32 de- sired depth, the merCluy column in a thermometer fas-
grees F (0 degrees C) in the polar regions to a high of tened to the outside is automatically fixed. TI1is records
about 85 degrees F in the Persian Gulf. The salinity of the exact temperature of the water when the bottle
seawater lowers its freezing point. We know that fresh turned over. In tllis way, temperatures at any depth in the
water freezes at 32 degrees F; seawater has a freezing ocean can be measured. -When brought to the surface, the
point of about 28 degrees F (-2.2 degrees C). On the deep water sample can also be tested for salinity, other chemi-
ocean bottOlll, hmvever, the cold, dense ,vater stays at a cal content, llUnute Inarine life, and so on.
uniform temperature of about 4 degrees C (39.2 degrees
F) all the time in all latitudes. THE COLOR OF WATER
An instrument called a bathythermograph, commonly
called an XBT, can be dropped from ships to check water In shallow places, the ocean's water appears light green,
temperatures at various depths (bathy means "depth," \vhile in deeper areas it seelns to be blue, gray, or dark
thermo stands for "temperature," and graph stands for green, These are colors seen -when the water does not