Iron fertilization is the intentional introduction of iron, an essential nutrient, to the upper ocean to stimulate the marine food chain, and/or to sequester carbon dioxide from the atmosphere . Fertilization supports the growth of marine phytoplankton blooms by physically distributing microscopic iron particles in otherwise nutrient-rich, but iron-deficient blue ocean waters. An increasing number of ocean labs, scientists and businesses are exploring it as a means to revive declining plankton populations, restore healthy levels of marine productivity and/or sequester millions of tons of CO2 to slow down global warming. Since 1993, ten international research teams have completed relatively small-scale ocean trials demonstrating the effect.
Fertilization also occurs when natural or artificial upwellings bring nutrient-rich deep-water up to the surface, as occurs when ocean currents meet an ocean bank or a sea mount. This form of fertilization produces the world's largest marine habitats. In rare cases, fertilization can occur when weather carries soil long distances over the ocean.
Martin's famous 1991 quip at Woods Hole Oceanographic Institution, "Give me a half a tanker of iron and I will give you another ice age, drove a decade of research whose findings suggested that iron deficiency was not merely impacting ocean ecosystems, it also offered a key to mitigating climate change as well. Martin hypothesized that increasing phytoplankton photosynthesis could slow or even reverse global warming by sequestering enormous volumes of CO2 in the sea. He died shortly thereafter during preparations for Ironex I , a proof of concept research voyage, which was successfully carried out near the Galapagos Islands in 1993 by his colleagues at Moss Landing Marine Laboratories. Since then 9 other international ocean trials have confirmed the iron fertilization effect:
Perhaps the most dramatic support for Martin's hypothesis was seen in the aftermath of the 1991 eruption of Mount Pinatubo in the Philippines. Environmental scientist Andrew Watson analyzed global data from that eruption and calculated that it deposited approximately 40,000 tons of iron dust into the oceans worldwide. This single fertilization event generated an easily observed global decline in atmospheric CO2 and a parallel pulsed increase in oxygen levels.
The Redfield ratio describes the relative atomic concentrations of critical nutrients in plankton biomass and is conventionally written "106 C: 16 N: 1 P." This expresses the fact that one atom of phosphorus and 16 of nitrogen are required to "fix" 106 carbon atoms (or 106 molecules of CO2). Recent research has expanded this constant to "106 C: 16 N: 1 P: .001 Fe" signifying that in iron deficient conditions each atom of iron can fix 106,000 atoms of carbon, or on a mass basis, each kilogram of iron can fix 83,000 kg of carbon dioxide. The 2004 EIFEX experiment reported a carbon dioxide to iron fixation ratio of nearly 300,000 to 1. Assuming that data is on a mass basis, then the normalized atomic ratio would be approximately: "380,000 C: 58,000 N: 3,600 P: 1 Fe".
In "desolate" HNLC zones, therefore, small amounts of iron (measured by mass parts per trillion) delivered either by the wind or a planned restoration program can trigger large responsive phytoplankton blooms. Recent marine trials suggest that one kilogram of fine iron particles may generate well over 100,000 kilograms of plankton biomass. The size of the iron particles is critical, however, and particles of 0.5~1 micrometre or less seem to be ideal both in terms of sink rate and bioavailability. Particles this small are not only easier for cyanobacteria and other phytoplankton to incorporate, the churning of surface waters keeps them in the euphotic or sunlit biologically active depths without sinking for long periods of time.
Of the carbon-rich biomass generated by natural plankton blooms and fertilization events, half or more is generally consumed by grazing organisms (zooplankton, krill, small fish, etc.) but 20 to 30% sinks below 200 meters into the colder water strata below the thermocline. Much of this fixed carbon continues falling into the abyss as marine snow, but a substantial percentage is redissolved and remineralized. At this depth, however, this carbon is now suspended in deep currents and effectively isolated from the atmosphere for centuries or more. (The surface to benthic depths cycling time for the entire ocean system is approximately 4000 years.)
Analysis and quantification: Evaluation of the biological effects and verification of the amount of carbon actually sequestered by any particular bloom requires a variety of sophisticated measurements. Methods currently in use include a combination of ship-borne and remote sampling, submarine filtration traps, tracking buoy spectroscopy, and satellite telemetry.
During the Southern Ocean Iron Enrichment Experiments (SOFeX), DMS concentrations increased by a factor of four inside the fertilized patch. Widescale iron fertilization of the Southern Ocean could lead to significant sulfur-triggered cooling in addition to that due to the increased CO2 uptake and that due to the ocean's albedo increase, however the amount of cooling by this particular effect is very uncertain.
Since NASA scientists have reported a minimum 6~9% decline in global plankton production since 1980 (and other scientists report 10~12% losses), this suggests that a full-scale international plankton restoration program could regenerate approximately 3~5 billion tons of carbon sequestration capacity worth €75 billion or more in carbon offset value. Iron fertilization is a relatively inexpensive carbon sequestration technology compared to scrubbing, direct injection and other industrial approaches, and can theoretically generate these credits for less than €5/ton CO2e.. Given this potential return on investment, some carbon traders and offset customers are watching the progress of this technology with interest.
We do not know the possible side-effects of large-scale iron fertilization. Not enough research has been done. We should not risk iron fertilization on the scale needed to affect global CO2 levels or animal populations. Creating blooms in naturally iron-poor areas of the ocean is like watering the desert: you are completely changing one type of ecosystem into another. Advocates argue that iron addition would help to reverse a supposed decline in phytoplankton, but this decline may not be real. While one study (Gregg and Conkright, 2002) reported a decline in ocean productivity between the period 1979–1986 and 1997–2000, another study (Antoine et al., 2005) found a 22% increase between 1979–1986 and 1998–2002. Gregg et al. 2005 also reported a recent increase in phytoplankton.
Advocates argue as follows.
Similar blooms have occurred naturally for millions of years with no observed ill effects and that not even trying to remedy these industrial impacts is far more irresponsible considering the known pace of increasing harm.
The counter-argument to this is that the low sequestration estimates that emerged from some ocean trials are largely due to three factors:
Some ocean trials did indeed report remarkable results. According to IronEx II reports, their thousand kilogram iron contribution to the equatorial Pacific generated a carbonaceous biomass equivalent to one hundred full-grown redwoods within the first two weeks. Researchers on Wegener Institute's 2004 Eifex experiment recorded carbon dioxide to iron fixation ratios of nearly 300,000 to 1.
Current estimates of the amount of iron required to restore all the lost plankton and sequester 3 gigatons/year of CO2 range widely, from approximately two hundred thousand tons/year to over 4 million tons/year. Even in the latter worst case scenario, this only represents about 16 supertanker loads of iron and a projected cost of less than €20 billion ($27 Billion). Considering EU penalties for Kyoto non-compliance will reach €100/ton CO2e ($135/ton CO2e) in 2010 and the annual value of the global carbon credit market is projected to exceed €1 trillion by 2012, even the most conservative estimate still portrays a very feasible and inexpensive strategy to offset half of all industrial emissions.
Advocates: Ocean science does traditionally define "sequestration" in terms of sea floor sediment that is isolated from the atmosphere for millions of years. Modern climate scientists and Kyoto Protocol policy makers, however, define sequestration in much shorter time frames and recognize trees and even grasslands as important carbon sinks. Forest biomass only sequesters carbon for decades, but carbon that sinks below the marine thermocline (100~200 meters) is effectively removed from the atmosphere for hundreds or thousands of years, whether it is remineralized or not. Since deep ocean currents take so long to resurface, their carbon content is effectively "sequestered" by any terrestrial criterion in use today.
Advocates: Most species of phytoplankton are entirely harmless, and indeed beneficial. Red tides and other harmful algal blooms are largely coastal phenomena and primarily affect creatures that eat contaminated coastal shellfish. Iron stimulated plankton blooms only work in the deep oceans where iron deficiency is the problem. Most coastal waters are replete with iron and adding more has no effect. Since all phytoplankton blooms last only 90~120 days at most, in the open ocean fertilized patches of any species will dissipate long before reaching any land.
Advocates: The largest plankton replenishment projects now being proposed are less than 10% the size of most natural wind-fed blooms. In the wake of major dust storms, many extremely vast natural blooms have been studied since the beginning of the 20th century and no such deep water dieoffs have ever been reported.
Advocates: CO2-induced surface water heating and rising carbonic acidity are already shifting population distributions for phytoplankton, zooplankton and many other creatures on a massive scale.
If certain infusions or space/time coordinates do show asymmetrical selective impacts in certain regions, the effect is inherently constrained by the limited size and 90-day lifespan of each bloom. Only larger scale research will show if this is really a problem, what factors tilt the playing field, and/or whether this issue can be effectively addressed.
Advocates say that using this technique to restore ocean plankton to recent known levels of health would help solve half the climate change problem, revive major fisheries and cetacean populations, and alleviate several other urgent ocean crises. Critics say global warming must be solved at the source, large scale iron fertilization experiments have never been attempted, the effects could be inadequate, and/or too little is known to press ahead.
Critics and advocates generally agree that most outstanding questions on the impact, safety and efficacy of ocean iron fertilization can only be answered by much larger studies. One pilot project planned by a U.S. company called Planktos was cancelled in 2008 after it was opposed by environmental groups.