Scientists Protest Ocean Iron Enrichment to Capture CO2

For the first time (I think), a group of oceanographers have written a letter to one of the top tier science research journals, Nature, warning against the use of ocean iron fertilization experiments to as a way to sell carbon credits.  Thr group includes a number of highly accoladed researchers in the field, many of whom have themselves organized such enrichment experiments.  According to the authors (subscription required):

The consequences of global climate change are profound, and the scientific community has an obligation to assess the ramifications of policy options for reducing greenhouse gas emissions and enhancing CO2 sinks in reservoirs other than the atmosphere[...]

[...]The efficacy by which OIF sequesters atmospheric CO2 to the deep sea remains poorly constrained, and we do not understand the intended and unintended biogeochemical and ecological impacts. Environmental perturbations from [ocean enrichment experiments] OIF are nonlocal and are spread over a large area by ocean circulation, which makes long-term verification and assessment very difficult. Modeling studies have addressed sequestration more directly and have suggested that OIF [...] would be unlikely to sequester more than several hundred million tons of carbon per year. Thus, OIF could make only a partial contribution to mitigation of global CO2 increases.

Despite these uncertainties in the science, private organizations are making plans to conduct larger-scale iron releases to generate carbon offsets. We are convinced that, as yet, there is no scientific basis for issuing such carbon credits for OIF.

Why Iron Enrichment?
In the 1980's, scientists were trying to determine why there were large expanses of the global ocean that had excess plant nutrients.  This indicated that a particular variable was preventing the single celled plant-like cells (phytoplankton) that grew there from using them up.  After a dozen or so large-scale experiments, and nearly 15 years of research later, oceanographers are confident that these areas of the ocean lack a very important nutrient: iron.

Iron is required by nearly all living things.  It's a member of the transition element family on the periodic table, and, like many of its brethren, has the capacity to move electrons between different molecules.  This atribute is invaluable when it comes to organismal metabolism, since electron transfer reactions lie at the heart of how our cells make energy everyday.  In fact, some estimates put greater than 90% of the total iron of a phytoplankton cell inside the chloroplast, the intracellular subcompartment whose molecular machinery turns carbon dioxide, with the help of light, into sugars

So, when you don't have enough iron (like a human anemic), you don't do very well.  In the case of phytoplankton, they aren't able to produce the sugars they require to grow, as well as a number of other very important metabolic processes iron is involved in.

Why Is Iron Limiting?
This is a complex question to answer, but the short version is: there isn't enough iron reaching the limited areas, and what is present in the water is in a chemical form that is more difficult to use than areas where there is a larger input of iron.  The result: growth limitation.

Why Carbon Credits?
Well, as I said above, phytoplankton turn carbon dioxide into sugars.  This process, often referred to as "carbon fixation" (i.e. "fixing" carbon from a gaseous state into non-gaseous state), draws CO2 out of the water.  Now, if these cells happen to sink below the surface layer of the ocean that is in constant contact with the atmosphere (via wind mixing), then that CO2 that was fixed is no effectively removed from the atmosphere, or "sequestered".

What's The Problem?
Therefore, the companies propose to use this sequestering phenomenon as a way to sell carbon credits to polluting companies.  The problem is, we don't know nearly enough about the phenomenon and the implications of larger scale (both spatially and temporally) "dumpings" of iron into the ocean.

There are a number of potentially disastrous impacts OIFs could have, many of which, without going into detail, are real and not the result of wild speculation (i.e. large-scale anoxic bottom water events that kill all the fauna present, the biological production of other, nastier greenhouse gases as a byproduct, no significant effect at all on carbon sequestration form the atmosphere).  In fact, OIFs could do much more harm than good on a global scale, especially if left to companies whose bottom line might supercede science.