Iron Fertilization Science Summary of Iron Fertilization Principles
1.All Plants Need Iron, But Very Little Iron –
Iron is a micronutrient essential for the synthesis of enzymes required for photosynthesis. In relatively rare cases where terrestrial plants lack iron, they cannot manufacture sufficient chlorophyll, such as those to the left. The amounts plants need, however, are small; a mature two-ton tree will need about 40 grams.
2. Most Ecosystems Have More Than Enough Iron – Terrestrial plants seldom lack iron becau most soils have abundances of iron. Most ocean waters are supplied by iron from river and bottom sediments or by clouds of dust that can travel for thousands of miles. To see satellite images of Asian dust storms over the Pacific see: http://cimss.ssec.wisc.edu/goes/misc/980424.html
3. Some Ocean Waters Are Iron-Deficient – Marine ecosystems generally do not recycle iron. When microscopic plants die, the iron they have absorbed sinks. Unless iron is constantly replenished from sediments or atmospheric dust, waters far from land can become iron-deficient. Lack of iron is one reason why the density of phytoplankton varies by more than one hundredfold, as illustrated by the map to the right, which show differences in phytoplankton abundance, measured as chlorophyll concentrations, in the world’s oceans
4. Iron-deficient Waters Often Have Ample Amounts of Other Nutrients. Large areas of the Pacific and Southern Oceans have what are called High-Nutrient, Low-Chlorophyll (HNLC) waters. Before the importance of iron was recognized, scientists had puzzled why these waters, which sailors had called “The Desolate Zones”, with their “chicken-soup” nutrient levels, had so few plants.
5. When Iron Is Added to HNLC Waters, Phytoplankton Grow Rapidly. Within days, the concentrations of plants can increase tenfold or more. This would be analogous to going from a desert to a rainforest within a week in terrestrial systems.
6. When phytoplankton have consumed the available nutrients, they sink to deeper waters. Within roughly two weeks after the addition of iron, phytoplankton deplete the supply of available macronutrients. Maintaining buoyancy requires energy, so when photosynthesis stops, the heavier diatoms sink below the thermocline.
7. When entrained in deeper waters, carbon is distributed by currents, remineralized, and some portion sinks. Once diatoms sink below the thermocline, they begin a slow process in which they decompose into inorganic carbon which dissolves in the deep, cold currents. Some portion of the diatoms may sink to the bottom sediments. So carbon entrained by specific bloom will be distributed over a large vertical and horizontal area.