I'm primarily going to be giving you a perspective of someone who was there when iron fertilization experiment happens. I will focus on the FeEx II experiment conducted in 1995. There are colleagues here today from New Zealand, Holland, and Germany who were on the Southern Ocean Iron Release Experiment (SOIREE) cruise and can speak to those experiments.

imageI'm going to address some of the issues that face us as oceanographers, some of which are new to us both as scientists and as citizens of a smaller and smaller planet. Iron enrichment experiments are catapulting many of us into a new era, and I think we really welcome the opportunity to advance this discussion on the use of iron enrichment experiments. I would suggest that there's both danger and opportunity in the way scientists advance this field, and it really is up to us as scientists to determine whether this poses a danger for our planet or an opportunity to advance the science.

imageAs several of us have mentioned, iron is critical for all life. It's used in ferrodoxin which is a protein that carries electrons throughout cells. It's needed in nitrate reductase, chlorophyll synthetase and other enzymes that are all critical for plant life.

Many of these proteins have genomic sequences that date far back in the geologic record and some sequences are estimated to be 3.5 billion years old. I mention this fact because life on earth evolved when the oceans and atmosphere were reducing environments without free oxygen and iron was abundant to organisms. It's a way of emphasizing that iron has played a key role in evolution and plant life on this planet.

imageTake a look at the distribution of iron in the ocean today. It's represented on this side by black dots. There are two things you should be aware of with respect to this profile. First, the concentration of iron in the surface waters is extremely low. They're on the order of picomolar concentrations; that is 10-12 moles per liter. Second, it has a nutrient-type distribution that mimics nitrate, indicating that iron plays a role-or acts as a nutrient-in some of these ocean systems.

For those who are not familiar with these concentrations, iron exists at the part per quadrillion level in seawater.


This is the equivalent to a postage stamp on the area of Texas. If you're a cell and you need iron to survive, it'd be like flying over Texas looking for a postage stamp.

In addition, these extremely low concentrations poses an analytical challenge to chemists measuring its concentration and many of us are struggling to develop chemical methods for the analysis that are robust and can use at sea.

imageTo reiterate some earlier points, this slide shows the stoichiometry of photosynthesis and respiration including the iron requirement for phytoplankton. The upper portion depicts photosynthesis indicating a conversion of CO2 into organic Carbon material that sinks from the water column into the deep ocean. To illustrate the molar ratio of Fe:CO2 required by a phytoplankton cell, you can move 20,000 carbon dioxide molecules over to this side of the equation with one iron atom in the coastal zone, and perhaps in the open ocean you can move 500,000 CO2 atoms with one iron atom.

This is an incredible leveraging of iron by the cell in a very delicate biological system. The point here is that very little iron is required to fix a lot of carbon dioxide.

What does this mean in ocean systems? In this gross oversimplification of the carbon cycle, we see the atmosphere represents about 700 metric tons of carbon, and acts as a reservoir.

imageThe oceans, by far, have the largest reservoir of carbon, which is accessible in the biosphere, representing about 38,000 metric tons of carbon.

What I want to emphasize here is that small differences in the balance of these carbon reservoirs can make huge differences in terms of climate.

imageThis is a schematic diagram of the biological pump in the ocean. These are complex, linked processes that result in the transport of carbon fixed in the surface water by phytoplankton to the deep ocean. If we turn-up the biological pump to drive more CO2 into the oceans, CO2 in the atmosphere may decrease.

Note that only a fraction of that CO2 that is incorporated via the biological pump actually exits into the deep sea and may in fact be sequestered.

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