4_LIFE_IN_THE_OCEAN.pdf - LIFE IN THE OCEAN Life in the...

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LIFE IN THE OCEAN
Life in the ocean is variable; much of how it operates is the same
as it is on the land. Animals that live in deserts have to adapt to
an environment, which is quite different from those that live in
the polar areas.
Just as the land has many variations, so does the ocean. The
ocean varies from shorelines where organisms need to cope with
periods of being underwater and sometimes totally exposed to
the air. The availability of food changes from area to area. In
each part of the ocean, there are different problems to deal with.
As one travels down the depths of the ocean, the most obvious
change is the loss of light. This change has been reflected in
labeling depths as to euphotic dysphotic and aphotic in which
there is enough light for photosynthesis, enough light to see by
(but not enough for photosynthesis and finally the depths where
there is no light at all.
Any aspect of the ocean may undergo a change. A cline is a point
at which some the aspect of the ocean changes radically. The
ones that are most important, are light, temperature
(thermocline), salinity (halocline), density (pycnocline), nutrient
concentration (nitrogenous plus silicic acid and phosphate)
(nutricline) and oxygen concentration.

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From the graphs of the clines, one can see there is a kind of “two
layered” structure – above and below 50 meters. The problem
here is that photosynthesis requires sunlight and nutrients. Above
the 50 meter level there is enough light, but the nutrient level is
low. This tend to inhibit the growth of photosynthetic organisms.
This inhibits the development of animals further along the trophic
chain. (primary producers=> grazers=>predators).
The bottom layer of the ocean below the thermocline, has the
reverse problem. There are enough nutrients and the top portion
has enough oxygen – but not enough light so no phytoplankton
(autotrophic plankton). So the top is no better than the bottom.
So of the 2 layers, neither is really set up to support life. As
Denny says “It’s a lousy way to run a planet!”)

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The light intensity falls of based on the idea that the deeper one
goes, the more the light is blocked by the water.
Temperature falls off in a similar pattern. With the loss of
sunlight, there is also a loss of heat, so the temperature drops off
with decreasing light. There is also an important development in
the far north and south.
Sea water as it starts to get closer to freezing temperature (-1.89
C), begins to expel salts in a very saline brine, which begins to
sink since it is heavier and denser that the surrounding sea
water. The seawater that is beginning to freeze is getting closer
to being fresh water and hence floats. The descending cold saline
water while becoming warmer and less salty as it mixes with the
surrounding water is still the saltiest and coldest water around.