Affect
of UV Radiation on Oceanic Plankton
By Rita
Johnson
With global warming becoming a growing concern, it is becoming more and more important to look at how it will affect the Earth. Questions arise as to how global warming will affect plants, animals, ecosystems and the human race. The Earth runs as a system of interacting components. A change in any one part of the system, no matter how great or small will indeed yield changes in some other part of the system. We are going to look at of the smallest parts of the system, oceanic plankton. What is the contribution of this component? Does it play a significant role? How will/has increased UV radiation due to global warming affect/ed oceanic phytoplankton? Are these changes significant?
Global Warming
How
does it relate to increased UV radiation?
An increase
in UV radiation can be linked to an increase in greenhouse gasses, primarily
Chlorofloufocarbons (CFCs). CFCs are chemicals that break down ozone, a
chemical naturally found in the Earth's stratosphere that can remain in
the Earth's atmosphere for up to 120 years. Ozone is crucial to the Earth's
atmosphere since it absorbs UV radiation. CFCs accumulate in the atmosphere
and are broken down into ClO and O2 by UV waves . A free oxygen atom collides
with this molecule to form Cl and O2. This Cl atom is free to destroy more
O3 molecules. (see below equation)
Cl
+ O3 ---> ClO + O2
ClO + O ---> Cl + O2
This deterioration of stratospheric ozone is most evident over Antarctica. Antarctica is surrounded by a Polar Vortex, which keeps the atmosphere over it separate from the rest of the atmosphere. In the winter, CFCs are able to accumulate in large amounts in this area since there is almost no sunlight to break them down. During the Austral Spring, UV radiation strikes these CFCs that accumulated during the long, dark winter. The breakdown of such a large amount of CFCs at once triggers the destruction of a large amount of ozone and causes a hole over Antarctica that contains no ozone. This exposes Antarctica and the Antarctic Ocean to large amounts of UV radiation.
Phytoplankton
What
is Phytoplankton?
Phytoplankton are small one-celled organisms that convert inorganic compounds
into organic compounds. They are found in oceans and other bodies of fresh
and salt water. Phytoplankton are fragile creatures that require a stable
environment to survive. Any change in phytoplankton concentrations can
indicate changes in the atmosphere or environment.
Phytoplankton
and the Environment
Phytoplankton serve as a base for the aquatic food chain. It is eaten by
zooplankton, which is eaten by krill. Krill serve as food for a number
of aquatic animals including penguins, whales and anchovy. A decline in
the phytoplankton population can cause food shortages and eventually a
decline in other animal populations. A study done on Adelie penguins by
the Polar Oceans Research Group found a 40% decline in penguin populations
since 1972. This decline can be attributed in part to a decline in oceanic
phytoplankton.
In addition to supporting the food chain, phytoplankton aids in reducing
global temperature. Phytoplankton reduces the amount of CO2 in the atmosphere
by photosynthesizing CO2 dissolved in the ocean. Phytoplankton is
responsible for over half of the photosynthetic activity on Earth. This
helps to reduce global warming since CO2 is a greenhouse gas.
Impacts
How
does this impact the rest of the world?
A 2- 4% decrease in phytoplankton productivity may seem small, but as the
ozone hole increases in size this decrease in productivity may also cause
a rise in temperature. According to the Scripps
Photobiology Group, oceanic phytoplankton is responsible for over
half of photosynthesis on Earth. At this level, phytoplankton accounts
for a large decrease in temperature. According to Greenpeace,
a 10% decrease in phytoplankton would decrease the annual oceanic uptake
of carbon by 5gT. Because of this, increased UV radiation causes a destructive
cycle. Global warming causes an increase in UV radiation which decreases
phytoplankton productivity. This allows more CO2 to stay in the atmosphere
and causes the atmosphere to warm. Some scientists worry that if this continues
to escalate, the global warming problem will only worsen. This decrease
will not only be bad for the environment in terms of temperature and global
warming, but it will also pose a threat to many animals and ecosystems.
Since phytoplankton is present in salt water and fresh water ecosystems,
as the ozone hole spreads to Northern hemisphere continents, the impact
may be seen in land animals as well as marine animals. This could mean
an even bigger impact on human populations.
Proposed
solution.
In 1995 the Southern
Ocean Iron Release Experiment (SOIREE) was conducted in the Ross sea.
Scientists in this experiment proposed that iron would boost phytoplankton
productivity in oceans that were iron deficient. Over 13 days iron was
released into a patch of water. Phytoplankton levels were monitored over
this time period. The experiment found that the patch increased by 6 times
its original biomass. Large phytoplankton became the bulk of the biomass
growing from 50% to around 70%. CO2 levels were significantly lower inside
the patch.
Some scientists look at the results of this experiment optimistically.
They propose that iron fertilization in the oceans could be the answer
to reducing global warming. Other scientists fear that ocean fertilization
is an improper solution to a growing problem that may have underlying repercussions.
Problems
1. One
problem involves where the carbon taken from the water actually goes. Experimenters
in SOIREE noticed a significant drop in CO2 levels, but exactly what happens
to the carbon in unknown. It seems obvious that phytoplankton photosynthesizes
CO2 and therefore reduce the amount of it in the atmosphere. However, in
the SOIREE experiment, over 80% of the plankton in the patch were large
phytoplankton (zooplankton and diatoms). Diatoms are covered by a silicone
shell. When these organisms die, carbon binds to their shell and the skeleton
sinks to the bottom since the organism is larger and heavier. Some scientists
theorize that if oceans were fertilized in this manner on a large scale,
there would be a lot of this carbon going to the bottom of the ocean at
once. They worry that this carbon may resurface after an unknown amount
of time and cause even more problems in the future.
2. Another
problem involves the organisms that rely on phytoplankton for survival.
Because small krill can only eat phytoplankton 20 micromters in diameter,
ocean fertilization may pose a threat to organisms that eat krill. In the
SOIREE experiment it was recorded that larger zooplankton were grazing
on smaller phytoplankton at a higher rate. If small krill cannot find phytoplankton
small enough to eat they will not be able to mature. The animals that rely
on krill for survival will then also be in danger.
3. The
third problem involves the extent to which an increase in oceanic phytoplankton
would actually cause the Earth's atmosphere to cool. In a 2002 study done
by the Scripps Institute, evidence was found supporting the suggestion
that phytoplankton could actually also contribute to global warming. The
study found that phytoplankton actually absorb UV radiation. According
to the Scripps Institute, this
absorption should account for 0.1 to 0.6 degrees of global mean temperature
increase. They fear that if the oceans were fertilized with iron on a large
scale, the net cooling affect could be countered or possibly overshadowed
by this absorption warming affect. This could possibly lead to an increase
in global mean temperature.
4. A
massive iron fertilization project could cos between 10 and 110 billion
dollars. Currently the government spends less than 2 billion dollars per
year on global warming research. It is unlikely that the government will
fund such an expensive project without sufficient evidence supporting its
success. Some research is still being done in order to gain support for
ocean fertilization.
Conclusion
Although phytoplankton is one of the smallest organisms in our ecosystem,
it is also one of the most important. Not only is it an indicator of environmental
change, but it also serves as the base of the marine food chain. It is
important to evaluate the effects of changes on the environment on phytoplankton
because it supports so many creatures. A change in the smallest of organisms
can foreshadow larger changes to come. Some of these changes have already
been seen.
In 1995 the death of a large amount of Antarctic penguins was attributed
to a krill shortage most likely caused by reduced amounts of oceanic phytoplankton.
In Australia reports of large cases of blind kangaroos was linked to an
immune system deterioration caused by increased UV radiation. In parts
of South America that are becoming more and more effected by the ozone
hole, cases of sheep developing cataracts were attributed to increased
UV radiation. These are just a few of many scary indicators that global
warming is becoming a growing problem that will inevitably affect the human
race. There is no doubt to the fact that something must be done to combat
the global warming problem. The only question that remains asks if the
larger countries of the world will step up and try to solve the problem
at its source. Or will they continue to look for quick fixes such as oceanic
fertilization to solve the problem they have created.