Phytoplankton SoAtlantic 20060215

An oceanic phytoplankton bloom

Iron fertilization is the intentional introduction of iron to the upper ocean to increase the marine food chain and to sequester carbon dioxide from the atmosphere [1]. It involves encouraging 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.


Consideration of iron's importance to phytoplankton growth and photosynthesis dates back to the 1930s when English biologist Joseph Hart speculated that the ocean's great "desolate zones" (areas apparently rich in nutrients, but lacking in plankton activity or other sea life) might simply be iron deficient. Little further scientific discussion of this issue was recorded until the 1980s, when oceanographer John Martin renewed controversy on the topic with his marine water nutrient analyses. His studies indicated it was indeed a scarcity of iron micronutrient that was limiting phytoplankton growth and overall productivity in these "desolate" regions, which came to be called "High Nutrient, Low Chlorophyll" (HNLC) zones.

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," vernacularized a decade of research findings that suggested iron deficiency was not merely impacting ocean ecosystems, it also offered a key to mitigating climate change as well. Martin hypothesized that restoring high levels of plankton 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 [2], 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:

  • Ironex II , 1995[3]
  • SOIREE (Southern Ocean Iron Release Experiment, 1999 [4]
  • EisenEx (Iron Experiment)], 2000 [5]
  • SEEDS (Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study), '01 [6]
  • SOFeX (Southern Ocean Iron Experiments - North & South), 2002 [7]
  • SERIES (Subarctic Ecosystem Response to Iron Enrichment Study), 2002 [8]
  • SEEDS-II, 2004[9]
  • EIFEX (European Iron Fertilization Experiment), 2004[10]
  • CROZEX (CROZet natural iron bloom and Export experiment), 2005 [11]

Perhaps the most dramatic vindication of 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. [12]


There are several key issues fueling interest in this technology, including ecological, climatic and financial concerns.

Ecological issues[]

NASA and NOAA recently reported that since the early 1980s marine phytoplankton populations have declined by over 20% in the Pacific Ocean and 6~9% globally. Since these plankton constitute the base of the entire marine food pyramid, their declining numbers mean less nourishment for all other marine species. This relationship was dramatized by the great plankton dieoff along America's Pacific Coast in the summer of 2005 that littered California beaches with thousands of fish and seabirds that had starved to death.


Marine Food Web

Most concerning, the southern ocean krill populations that feed directly on phytoplankton have plummeted nearly 80% over the same period. These small crustaceans are the primary food for penguins, other seabirds, many commercially important fisheries, and the most endangered whale species. Ocean scientists from Germany's Alfred Wegener Institute have in fact suggested that a large scale plankton restoration program in the cetacean nursery zones of the southern ocean could help return the krill-dependent great baleen whales (blue, humpback, gray, right, etc.) to healthy levels again in 10~20 years. This could also potentially benefit fisheries.

Besides recharging the marine food chain, iron-catalyzed plankton restoration could help reduce ocean surface acidification that has increased tenfold in the last two decades threatening the integrity of diatoms, foraminifera, coral and other creatures with acid-vulnerable carbonate skeletons. (Rising levels of atmospheric carbon dioxide increase concentrations of carbonic acid in surface waters, but phytoplankton blooms absorb large volumes of CO2 during photosynthesis and help buffer the acidity.)

Climatic effects[]

As John Martin envisioned from his water research and the paleoclimatological record, increasing plankton photosynthesis and primary productivity could have profound impacts on atmospheric CO2 and global temperature.

Historically marine phytoplankton have annually absorbed and fixed nearly half of all planetary CO2 emissions or approximately 50 billion tons. NASA and NOAA's most conservative estimate of global plankton decline in the last 25 years is at least 6%. Simply returning these populations to known 1980 levels of health and activity could therefore annually sequester 2~3 billion more tons of CO2 than are being removed today or a third to one half of all current industrial and automotive emissions. Also, water with more algae has a higher albedo, it would reflect more sunlight and cause less heating of the ocean (see image at top).

Financial opportunities[]

Since the advent of the Kyoto Protocol several countries and the European Union have established carbon offset markets which trade certified emission reduction credits (CERs) and other types of carbon credit instruments internationally. In 2006 CERs sell for approximately €25/ton CO2e, which suggests that a full-scale plankton restoration program could generate up to €75 billion 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. Given this potential return on investment, some carbon traders and offset customers are watching the progress of this technology with interest. However, Planktos Corporation, which has proposed engaging in iron fertilization, has been unable to raise sufficient capital to engage in operations. The firm blames their failure on success of a "highly effective disinformation campaign".[13][14]


The role of iron[]

File:Phytoplankton experiment.jpg

Phytoplankton experiment (1/8 tsp. phytoplankton added to each cup with iron added to left cup) after 20 hours.

About 70% of the world's surface is covered in oceans, and the upper part of these (where light can penetrate) is inhabited by algae. In some oceans, the growth and/or reproduction of these algae is limited by the amount of iron in the seawater. Iron is a vital micronutrient for phytoplankton growth and photosynthesis that has historically been delivered to the pelagic sea by wind-driven dust storms from arid lands. This Aeolian dust contains 3~5% iron and its deposition has fallen nearly 25% in recent decades due to modern changes in land use and agricultural practices as well as increased greening of dry regions thanks to increasing levels of atmospheric CO2. (Arid zone grasses and vegetation now lose less water vapor through their stomata to absorb the same amount of carbon dioxide, and thus stay greener longer, reducing dust storm frequency and the amount of iron reaching the deep seas. Increasing sand desertification does little to compensate for this shortfall since sand is primarily silica with relatively low iron content.)

The Redfield ratio describes the relative molecular concentrations of critical nutrients in plankton biomass and is conventionally written "106 C: 16 N: 1 P." This expresses the fact that one molecule of phosphorus and 16 of nitrogen are required to fix 106 carbon molecules. Recent research has expanded this constant to "106 C: 16 N: 1 P: .001 Fe" signifying that in iron deficient conditions each molecular unit of iron can fix over 100,000 units of carbon or 367,000 units of CO2.

In "desolate" HNLC zones, therefore, small amounts of iron (measured in parts per trillion) delivered by either by the wind or a planned restoration program can trigger large responsive phytoplankton blooms. Recent marine trials confirm that one kilogram of fine iron particles can reliably generate well over 100,000 kilograms of plankton biomass. The size of the iron particles is critical, however, and particles of several micrometres 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.

Carbon sequestration[]

Plankton that generate calcium or silica carbonate skeletons, such as diatoms, coccolithophores and foraminifera, account for most direct carbon sequestration. When these organisms die their carbonate skeletons sink relatively quickly and form a major component of the carbon-rich deep sea precipitation known as marine snow. Marine snow also includes fish fecal pellets and other organic detritus, and can be seen steadily falling thousands of meters below active plankton blooms[15].

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.

Dimethyl sulfide and clouds[]

Some species of plankton produce Dimethyl sulfide (DMS), a portion of which enters the atmosphere where it is oxidized by hydroxyl radicals (OH), atomic chlorine (Cl) and bromine monoxide (BrO) to form sulfate particles and ultimately clouds. This may increase the albedo of the planet and so cause cooling.

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 cooling in addition to the increased CO2 uptake, however the amount of cooling is very uncertain. [16]


While many advocates of ocean iron fertilization see it as modern society's last best hope to slow global warming long enough to change our consumption patterns and energy systems, a number of critics have also arisen including some academics, deep greens and proponents of competing technologies who cite a variety of concerns. [17] Penny Chisholm of MIT is a prominent critic, warning against possible unintended consequences of widespread employment of fertilization. Planktos is a company which proposes carrying out iron fertilization as a commercial method of carbon sequestration. [18] as is Michael Markels of [[Ocean Farming Inc]] which proposes a project in the territorial waters of the Marshall Islands. [19]

Precautionary Principle[]

Critics: We don’t 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.

Advocates: Similar blooms have occurred naturally for millions of years with no observed ill effects. The precautionary principle provides a legitimate brake on this technique once plankton populations are restored to their known levels in 1980. Up to that point, however, plankton revival is simply eco-healing and little different from remedially treating superfund sites, oil spills or contaminated mothers' milk.

Not even trying to remedy these industrial impacts is far more irresponsible considering the known pace of increasing harm.


According to certain ocean iron fertilization trial reports, this approach may actually sequester very little carbon per bloom, with most of the plankton being eaten rather than deposited on the ocean floor, and thus require too many seeding voyages to be practical.[20]

The counter-argument to this is that the low sequestration estimates that emerged from some ocean trials are largely due to three factors:

  1. Timing: none of the ocean trials had enough boat time to monitor their blooms for more than 27 days, and all their measurements are confined to those early weeks. Blooms generally last 60~90 days with the heaviest precipitation occurring during the last two months.
  2. Scale: most trials used less than 1000 kg of iron and thus created small blooms that were quickly devoured by opportunistic zooplankton, krill and fish that swarmed into the seeded region.
  3. Academic conservatism: having an obviously limited data set and unique sequestration criteria (see Sequestration Definitions below), many peer-reviewed ocean researchers are understandably reluctant to project or speculate upon the results their experiments might have actually achieved during the full course of a bloom.

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 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. Considering EU penalties for Kyoto non-compliance will reach €100/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.

Sequestration definitions[]

Critics: In ocean science, carbon is not considered removed from the system unless it settles to the ocean floor where it is truly sequestered for eons. Most of the organic and inorganic carbon that sinks beneath plankton blooms is dissolved and remineralized at great depths and will eventually be re-released to the atmosphere, negating the original effect. [21]

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.

Ecological issues[]

Harmful Algal Blooms (HAB)[]

Critics: Some plankton species cause red tides and other toxic phenomena. How do we know what kind of plankton will bloom in these events? What will prevent toxic species from poisoning lagoons, tide pools and other sensitive ecosystems along our coasts?

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.

Deep water oxygen depletion[]

Critics: When organic bloom detritus sinks into the abyss, a significant fraction will be devoured by bacteria, other microorganisms and deep sea animals which also consume oxygen. A large bloom could, therefore, render certain regions of the sea deep beneath it anoxic and threaten other benthic species.

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.

Ecosystem alterations[]

Critics: Depending upon the composition and timing of delivery, these iron infusions could preferentially favor certain species and alter surface ecosystems to unknown effect. Population explosions of jellyfish, disturbance of the food chain with a huge impact on whale populations or fisheries are cited as potential dangers.

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.

Conclusion and further research[]

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. Several such large scale pilot projects (covering approximately 10,000 km²) are currently being organized for 2006 and 2007 in collaboration with various ocean institutes and university laboratories. Initial reports on their findings should be available by autumn 2006.

See also[]


  1. Jones, I.S.F.; Young, H.E. (1997). "Engineering a large sustainable world fishery". Environmental Conservation 24: 99-104. Retrieved on 2006-11-27.
  2. Ironex (Iron Experiment) I
  3. Ironex II, 1995
  4. SOIREE (Southern Ocean Iron Release Experiment), '99
  5. EisenEx (Iron Experiment), 2000
  6. SEEDS (Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study), 2001
  7. SOFeX (Southern Ocean Iron Experiments - North & South), 2002
  8. SERIES (Subarctic Ecosystem Response to Iron Enrichment Study), 2002
  9. SEEDS-II, 2004
  10. EIFEX (European Iron Fertilization Experiment), 2004
  11. CROZEX (CROZet natural iron bloom and Export experiment), 2005.
  12. Watson, A.J. (1997-02-13). "Volcanic iron, CO2, ocean productivity and climate". Nature 385: 587-588. DOI:10.1038/385587b0.
  13. Notice on the home page of Planktos Corp.
  14. "Venture to Use Sea to Fight Warming Runs Out of Cash" article by Andrew C. Revkin in The New York Times February 14, 2008
  15. Video of extremely heavy amounts of "marine snow" in the Charlie Gibbs Fracture Zone in the Mid-Atlantic Ridge. Michael Vecchione, NOAA Fisheries Systematics Lab. Published at Census of Marine Life website
  16. Wingenter, Oliver W.; Karl B. Haase, Peter Strutton, Gernot Friederich, Simone Meinardi, Donald R. Blake and F. Sherwood Rowland (2004-06-08). "Changing concentrations of CO, CH4, C5H8, CH3Br, CH3I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments". Proceedings of the National Academy of Sciences 101 (23): 8537-8541. Retrieved on 2006-11-27.
  17. 'Fertilizing' oceans could affect food chain, scientists say: Impact of adding iron is little understood article by Bruce Lieberman, San Diego Union-Tribune, February 14, 2004
  18. "Carbon Science" according to Planktos
  19. http://www-pord.ucsd.edu/~sgille/stpa35/geritol_reading.pdf "Is Iron Fertilization Good for the Sea?"
  20. Basgall, Monte (2004-02-13). Goal of ocean 'iron fertilization' said still unproved. Retrieved on 2006-11-27.
  21. http://web.mit.edu/chisholm/www/publications/fefert.pdf "Iron fertilization of the oceans: Reconciling commercial claims with published models"] P Lam and SW Chisholm (2002)

Changing ocean processes[]

Declining ocean productivity[]

Micronutrient iron and ocean productivity[]

Ocean biomass carbon sequestration[]

  • Antarctic Krill Provide Carbon Sink in Southern Ocean - British Antarctic Survey
  • Oceanic Sinks for Atmospheric CO2, J.A. Raven and P.G. Falkowski, June 1999, Plant, Cell and Environment, Vol.22 No. 6
  • Zooplankton Fecal Pellets, Marine Snow and Sinking Phytoplankton Blooms, Jefferson T. Turner, February 2002, Aquatic Microbial Ecology, Vol. 27 No. 1
  • Phytoplankton and Their Role in Primary, New and Export Production, Paul Falkowski et al., 2003, Ocean Biogeochemistry, Chapter 4, Ed. Michael J.R. Fasham, Springer 2003
  • Markels, M and R T Barber (2001) Sequestration of CO2 by Ocean Fertilization. Proc 1st Nat. Conf. on Carbon Sequestration, Washington, DC.

Ocean carbon cycle modeling[]

  • Carbon Dioxide Fluxes in the Global Ocean, Andrew Watson and James Orr, 2003, Ocean Biogeochemistry, Chapter 5, Ed. Michael J.R. Fasham, Springer 2003
  • Three-Dimensional Simulations of the Impact of Southern Ocean Nutrient Depletion on Atmospheric CO2 and Ocean Chemistry, J.L. Sarmiento and J.C. Orr, December 1991, Limnology and Oceanography, Vol. 36 No. 8

External links and further reading[]

Recent coverage[]



Adapted from the Wikipedia article, "Iron fertilization" http://en.wikipedia.org/wiki/Iron_fertilization