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.

    Because these organisms are so sensitive, they are affected by UV radiation first. In a study done in 1992, a 6% - 12% drop in phytoplankton productivity was found during the time of the spring ozone hole. This translates to a 2%-4% drop overall. According to Greenpeace, a 5% drop in phytoplankton productivity translates to a loss of 7% or 7 tons of fish per year.

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.

Sources