Page 230 - NS-2 Textbook

OCEANOGRAPHY 225

sea life in the area off western South America ,vas re- THE FOOD CYCLE IN THE SEA
duced by about 20 percent. Severe flooding occurred
across South America and the southern United States, Life in the ocean may answer many of the questions
about the origin of life and its historical past, as well as
and Australia and parts of the central United States ex-
help solve the problems of in1proving human life in the
perienced hotter conditions and severe drought.
A related effect called La Nilia ("little girl" in Span- future. The life cycle in the sea is of great in1portance to
everyone. Marine biologists are the scientists who are
ish) usually follows when the El Nifio subsides. The La
working to find the answers to some of these questions.
Nifta effect results m lillusually cold surface waters in the
Equatorial Pacific. Resulting global climate changes tend 111e life cycle is the chain of nahrral events in which
organic plants and anin1als take in foods and chemicals,
to be opposite those associated with El Nifio. In the con-
release wastes dming their lifetin1es, and then die and
tmental United States, durmg El Nino years tempera-
tures m the winter are warmer than normal m the North decompose. Bacterial, current, wave, and solar (Sun) en-
ergy rotate this material from the bottom of the sea
Central States and cooler than normal m the Southeast
bringing it back into the slmlight where the process of
and the Southwest. Durmg a La Nina year, wmter tem-
perahu'es are warmer than normal in the Southeast and photosynthesis regenerates new life.
In the sea, as on land, swllight supports the life cycle.
cooler than normal in the Northwest.
It does so through the process of photosy"thesis, the man-
The Red Tide al1d Black Sea. In the Red Sea, atmo-
spheric and sea conditions similar to El Nifio occasionally ufachrre of food in a green plant. In the sea, floating
chlorophyll-bearing (green-colored) phytoplankton are
occur. There, when the upwelling of cool water stops, the
the basic food producers of the sea. They provide the
surface layers become heated and bring about a popula-
proteins} starches, and sugars necessary to support
tion explosion (or bloom) of tiny red-colored phyto-
the sea's smallest life. Phytoplankton are the food for
plankton called dil1oflagellata. 111ey become so munerous
the zooplankton, tiny animals of many shapes, which are
that the water takes on a reddish colm; giving it the name
Red Tide (and giving the Red Sea its name). The Red Tide either free-floating or self-propelled. The zooplankton-
which also include the eggs and larvae of some larger
clogs the gills of fish, causing them to suffocate and
fishes-are the food for small flesh-eaters (carnivores) of
die. Millions of dead fish are washed ashore, and the re-
the ocean. In hu'n, the small carnivores are eaten by
sulting stench carries for miles. A similar event ocelli'S,
larger ones. Death and decay complete the cycle. 11,e or-
more rarely, along the east coast of Florida. Some years
ganic material of both plants and anin1als decays as the
ago, many resorts and bathing beaches had to close
result of bacterial action, thereby releasing again the
down lmtil the Red Tide passed and the dead fish were
cleared away.
The Black Sea is essentially a very large saltwater
lake. Its only opening is through the Tmkish straits
(Bosporus and Dardanelles) to the Aegean Sea. The
straits are very shallow, so there is little exchange of
'water behveen the hvo seas, and no chance for up,velling
or the introduction of dissolved oxygen in the Black Sea.
As a result, the Black Sea is stagnant. The residue of ma-
rine life in the smface layers sinks to the bottom and re-
mains there to decay.
The decay of animal and vegetable matter uses up
whatever oxygen is available and creates hydrogen sul-
fide gas. Over thousands of years, this gas and lack of
oxygen have completely destroyed bottom life m the
Black Sea. The hydrogen sulfide layer begins about 200
feet below the surface and continues to the bottom. There
is no life in this J'black zone," which has given its name
to the sea.
For navies, the Black Sea poses a special problem.
Hydrogen sulfide gas, 'when mixed with 'vater, has a COf-
rosive effect on metals. Recall the Callao Pail1ter turning
the sides of ships black. A submarine operating for long The life and food cycle in the ocean. Beginning with the phyto-
plankton, which live on the nutrients and decayed matter from the
periods of time in the hydrogen sulfide zone would run
sea bottom that upwell into the lighted zone, the cycle moves
a serious risk of ruining her hull fittings, thereby endan- around to where dead animals drop to the bottom, providing the
gering the boat and her crew. matter upon which phytoplankton live, to begin the cycle anew.