Is Iron Fertilisation of the Oceans Safe?

It is often said we know more about the surface of the Moon than we do about the ocean floor, and during the filming of the BBC documentary "Blue Planet", [n] new species were discovered. Both ocean dynamics and ecology are areas of fascinating study and research, with plenty yet to be found out.

The ocean is turbulent and boundless. Control and reliable monitoring of large-scale iron-additions is simply not possible.

By definition, the proposal to add tonnes of iron to the ocean is with intent to change the natural ecology, to subsequently change the dynamics. This, in itself, is a cause for concern.
These attempts may be termed "geoengineering the ocean biogeochemistry" - or, "eco-hacking the ocean". Whatever it is called, such attempts with our incomplete understanding is fraught with known, and unknown, dangers.

There is plenty we don't know - both processes that we know we don't know, and no doubt some we don't even know about. Ignorance, in this case, is not bliss.

Ecological Effects

Is Marine Ecology Affected? Community Changes

By design, fertilisation will increase phytoplankton, which is the base of the marine food chain. Krill and other marine animals consume phytoplankton, so this increased food-supply could 'filter-up'. It is possible, and hoped, that this increase in food supply could boost stocks of all marine life. This would increase fisherman's catches from the over-fished seas, and even help restore whale populations, which are not yet recovering from over-hunting.

However, experiments show that artificial iron fertilisation causes community (species composition) change. While experimentation is aimed at increasing phytoplankton, SOFex showed that iron availability also affected a wide variety of bacteria, protozoa and micro algae - suggesting further, unknown consequences and difficulties in monitoring.

Disruption of the food chain's base will cause repercussions throughout, and may disturb dependencies. Furthermore, changed communities could be undesirable, or even toxic.

Observed community changes vary in the different seas.
In the North (SEEDS), the iron supply led to floristic shifts that resulted in the dominance of chain-forming large centric diatoms, whereas in the equatorial Pacific and the Southern Ocean iron stimulated the growth of pennate diatoms. The earlier southern experiments showed a preference for pennate diatoms over flagellates.

Are ecological effects limited to the fertilised areas?

As iron-limitation is removed, the other nutrients (nitrates, phosphorus, and silicates) are 'used up' by phytoplankton in the fertilised patch. Down-current communities reliant on their availability consequently suffer. Artificially increasing phytoplankton in some areas may simply move production up-current, disrupting existent ecologies while providing no overall increase.

What happens below the surface?

As atmospheric levels of carbon dioxide increase, so too does ocean-uptake. This additional CO₂ increases the ocean's acidity. Marine organisms such as coccoliths and corals are already suffering and showing deformities dues to this changed pH.

If, as has been emphatically proved, ocean iron fertilisation produces more phytoplankton, at least some will sink. Some will (aerobically) decompose, a process which uses up oxygen and generates carbon dioxide. This CO₂ will worsen the acidity problem.

Deeper down, anoxic 'dead' zones will form (because of the aerobic decomposition). Here, anoxic (methanogenic) bacteria produce methane and nitrous oxide, which are both far more powerful greenhouse gases than is carbon dioxide. (Methane is 24 times as powerful, nitrous oxide 206 times). Thus, increased phytoplankton-decay could produce additional, potent, greenhouse gases.

On the sea floor, a small proportion of organic carbon may get buried. Most will remain in suspension or dissolved in the water, later upwelling. Its removal from the surface is thus only temporarily.

Chemical Effects

Is the added iron safe?

Despite stringent legal restrictions of what-can-be-dumped, the presumed good intent of those involved, and assurances of the harmlessness of 'high-street garden-fertilisers', the chemicals proposed do not mimic natural iron. In some patents, an artificial chelator, lignin acid sulfonate, is used to prevent iron precipitation. It is 'chemically different from atmospheric iron sources.' [1]

What ocean chemical changes may occur?

• As already described, ocean acidity may increase as phytoplankton (and increased marine organisms) decompose.
• Phytoplanktonic algae produce dimethylsulphide (DMS), a gas which when released into the atmosphere influences cloud formation. Clouds in turn influence not only precipitation, but the Earth's albedo and thus temperature. Neither the resultant altered cloud formation, nor the exact influence of different cloud formations, is clear. It is generally accepted that DMS tends to lead to cooling overall, 'all other things being equal' - which they are not.
  (As mentioned in "Solar reflection", some phytoplankton absorb solar radiation, thus decreasing albedo and warming the Earth)
• Phytoplankton also produce compounds such as methyl halides - which cause ozone depletion.

References

• [1] "Dis-Crediting Ocean Fertilization" Sallie W. Chisholm,* Paul G. Falkowski, John J. Cullen. "Science" Volume 294, Number 5541, Issue of 12 Oct 2001, pp. 309-310.
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