Iron and its Effects on
the Carbon Cycle in Oceans

complied by
Bernadette Pate Holt

WSFC 611
Fall 1997

The rich plant life that can be found in our oceans is the major user of carbon dioxide from the atmosphere. Scientists now believe that the oceans currently absorb between 30 - 50% of the CO2 produced by burning fossil fuels. The rate of accumulation of C02 in the atmosphere depends on how much man emits and how much of this excess C02 is absorbed by plants and soil or is transported down into the depths by phytoplankton.

Phytoplankton:

Phytoplankton are tiny single-celled ocean plants containing chemical chlorophyll that use sunlight and carbon dioxide to create plant carbon. This plant carbon then becomes the beginning of the food chain for most of the planet. As phytoplankton grow and multiply, small fish and other animals eat them as food. Larger animals in turn feed on the smaller animals.

Carbon dioxide amounts in the atmosphere and dissolved in the ocean's surface layer determines the ocean-water absorption and emission of gas. The amount of gas dissolved in water in turn is influenced by the amount of phytoplankton which consumes C02 during photosynthesis. The most active occurrence of phytoplankton is within the first 50 meters of the surface and varies widely according to the season and location.

Phytoplankton caries gases and nutrients from the ocean surface to the deep. They absorb CO2 during photosynthesis and transport them into the deep ocean by the way of dead plant, body parts, and feces. C02 is then released into the water as the materials decay, and then becomes absorbed in the sea-water by combining chemically with water molecules.

Phytoplankton create a chemical substance called dimethylsulfide (DMS) that may promote the formation of clouds over the oceans which in turn creates changes in the plankton population. These changes in plankton population again may lead to changes in cloudiness. The more clouds would reduce the amount of solar radiation reaching the oceans, which could reduce plankton activity. In this way climate has a large effect upon plankton.

Research Projects:

The National Science Foundation has been researching a project since 1990 in which iron is introduced into a certain ocean area. Since iron is the limiting nutrient for the plankton, the growth of plankton cannot increase unless the amount of iron present in the water increases. By introducing extra iron into the environment, plankton growth is accelerated. The increase in plankton allows for more carbon dioxide to be removed from the atmosphere.

In April, 1993 an experiment, IronEx I was conducted by a team of researchers at Moss Landing Marine Laboratory led by Kenneth H Coale. The addition of iron into the water caused an initial doubling of the amount of phytoplankton, and the rate of growth quadrupled. However, after only one day, the phytoplankton activity leveled off. This was also relatively ineffective in reducing the amount of carbon dioxide it the air above the waters where the iron sulfate was introduced. One reason for this is believed to be that there were also an increase in the amount of zooplankton, which consumes the phytoplankton. Another factor may be that the iron particles combined with organic material and became heavier, thus sinking to the bottom, removing them from the surface area. Since the area of carbon dioxide and phytoplankton interaction is only within the first fifty meters below the surface, the iron that had been trapped by organic material had been removed from this critical area.

In 1995 another experiment, (IronExII) was performed in the equatorial waters of the Pacific about 800 miles west of the Galapagos Islands. It was also conducted by MLML with the additional help from the Monterey Bay Aquarium Research Institute. This time, instead of dumping in all of the iron at once, the iron was added continuously over a week's time. This eliminated the problem of the iron immediately sinking to the ocean floors. An estimated 1000 pounds of iron was added over the period of a week. Within a week two million pounds of additional phytoplankton had grown. Concentrations of chlorophyll were increased by a factor of between 30 to 40. This increase was so great, it caused the waters to turn green. Increased concentrations of chlorophyll means an increased productivity of the phytoplankton, which in turn caused additional 2.3 million kg of carbon dioxide to be absorbed by the phytoplankton. At day ten into the experiment the concentration of carbon dioxide had gone down by 20%.

Another experiment (IronEx IIIl) was proposed to the National Science Foundation for funding. If it is approved, the experiment will fertilize a 46 kilometer area for one year. The researchers at MLML estimate that two billion tons of C02 could be removed from the atmosphere a year. With such knowledge about the global impact that basic marine organism can have, one might wonder what will happen to our planet if our oceans become over polluted.

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