Questions and Concerns


How it works

How would iron fertilization for carbon sequestration be done?

The most likely approach to applying iron fertilizer for carbon sequestration would be to produce carbon “crops” with large, temporary blooms in the open ocean. The sequence of a typical “crop” would be:

  • A “patch” of suitable open ocean water, a circle with a diameter of roughly 80 miles, would be selected, the baseline conditions described, and a control station established;
  • Ships would spread iron fertilizers over the patch at a rate of roughly 200 pounds of fertilizer (20 pounds of iron) per square mile;
  • Scientists would monitor baseline conditions, fertilizer application, and phytoplankton response, which would probably be:
    • Within 10-14 days, the phytoplankton would bloom to densities of 5-10 times their pre-fertilization condition;
    • Within 21-30 days, phytoplankton will have stopped growing, gone dormant, and sank into deeper waters.

This approach of creating a temporary fertilized patch follows the method used by larger scale oceanographic experiments to date. The approach also resembles the manner by which storms originating in the Asian deserts intermittently deliver iron-bearing dust to the Pacific and Southern Oceans.

How would iron fertilization experiments be monitored and the results measured?

Each “crop” would be monitored and measured by scientists following a protocol acceptable to the oceanographic community and environmental regulators. The minimum elements of the protocol would include:

  • Describing pre-fertilization and control site baseline conditions;
  • Monitoring fertilizer application;
  • Measuring increases in phytoplankton growth and describing changes in species composition, as well as other ecosystem changes ; and
  • Observing, sampling and estimating the proportion of carbon which moves into deeper water.

The monitoring and measurement of iron fertilization experiments is expected to rely increasingly upon remote sensing and automated sampling and analysis techniques. Surveillance satellites, autonomous underwater vehicles, and other more efficient methods for sampling and analyzing routine data will probably become the primary means of surveillance.

How much carbon dioxide would a typical “crop” sequester?

The operation described above, a 5,000 square mile application over one month, would sequester 100,000-200,000 tons CO2 equivalent. This is roughly equivalent to what one would expect a 1000-acre forest to sequester over a period of roughly 40 years.

Where would iron fertilization be done?

Iron fertilization would be most effective in growing phytoplankton in regions of the ocean with excess nutrients but little chlorophyll. The largest areas of such “High-Nutrient, Low-Chlorophyll” waters are the Southern Ocean, the Equatorial Pacific, and parts of the Northeastern and Northwestern Pacific.

How Much Would Iron Fertilization Cost?

There are two components of the cost of sequestering carbon using iron fertilization:

  • The price of the iron fertilizer and costs of applying them; and
  • The costs of scientific monitoring, measurement, and related studies.

The cost of sequestering carbon dioxide by means of iron fertilization, considering only the costs of applying fertilizer, are roughly estimated at $1.50 to $2.00 per ton. This estimate is based upon the following assumptions:

  • Fertilizer would be in the form of a chelate (such as the iron in commercial terrestrial plant fertilizer preparations) at a cost of $0.30/pound at 10% iron content;
  • The costs of transporting and spreading iron fertilizer using a commercial freight is estimated at roughly an additional $0.30/pound;
  • Initial increase in primary production triggered by iron fertilizer estimated at 10,000 pounds elemental carbon in biomass in response to one pound of iron; and
  • The losses of carbon due to respiration and recirculation of remineralized carbon is assumed at 80%, or, the sequestration efficiency of the original crop is 20%.

The costs of scientific monitoring and measurement of iron fertilization “crops” will vary depending upon such factors as whether an oceanographic vessel is chartered or whether conventional vessels serve as the base for monitoring and measurement operations and the degree to which remote sensing and automated sampling and analysis systems are employed. The costs of monitoring initial experiments are expected to be 5-10 times the costs of purchasing and applying fertilizers. If monitoring and measurement shifts from research to a more stantdardized protocols, the costs of monitoring will probably be less than the applied costs of the fertilizers.

How do the costs of iron fertilization compare with other means of controlling carbon?

At $2.00 ton CO2, iron fertilization would be one of the lowest cost means of managing carbon. The only large-scale terrestrial sequestration options with comparable costs are forest management and agricultural soil management, approaches which have serious disadvantages.

The costs of directly reducing carbon dioxide emissions are higher than $2/ton. The costs of fuel substitution, automotive fuel substitution, renewable energy subsidies, etc. are typically in the range of $60-80/ton CO2 or more.
Ecosystems effects

What are the potential ecosystem risks of iron fertilization?

The potential risks most frequently cited are:

  • Concerns that iron fertilization creates unusual and unstable communities of plants;
  • Risks of promoting growth of toxic organisms;
  • Concern that wide-scale fertilization could cause anoxia in deeper waters;
  • Concern that, if anoxic conditions develop, more potent greenhouse gases such as methane will be created.

Does iron fertilization create unstable plant communities?

In HNLC waters that lack iron, phytoplankton communities are dominated by very small species of plants. When iron fertilizers are applied to HNLC waters, diatoms typically dominate the phytoplankton population. When nutrients are eventually depleted, the diatoms sink.

The dominance of diatoms is a common feature of phytoplankton blooms triggered by a variety of natural causes. Diatoms dominate phytoplankton blooms in upwelling regions that support highly productive fisheries. Episodic phytoplankton blooms dominated by diatoms are a routine seasonal event in many coastal waters.

Will iron fertilization promote the growth of toxic organisms?

In coastal waters, overabundance of nutrients is often hypothesized to be a contributing factor in blooms of toxic phytoplankton such as Pfiesteria and the organisms responsible for “red tides”.

The organisms specifically implicated in toxic blooms of coastal waters have bottom-dwelling phases in their life cycles and are therefore not present in the deeper waters where iron fertilization would be performed.

“Algae blooms” in coastal waters are very different from the phytoplankton growth in the open oceans which iron fertilization would produce. Coastal blooms are much denser, typically 10-20 times the density of plants which iron fertilization would grow.

Would iron fertilization create anoxic conditions in deeper waters?

In coastal and inland waters, dense algae blooms routinely create anoxic conditions. The decomposition of phytoplankton biomass by oxygen-consuming bacteria deplete supplies of dissolved oxygen in deeper waters.
The results of some computer-simulation studies indicate that widespread and prolonged iron fertilization could create anoxic conditions in some portions of the deep oceans.

Before iron fertilization could be performed on a large scale, a scientific consensus on the likelihood of anoxia risks would be necessary. GreenSea Venture and other entities are currently simulating large-scale fertilization with more sophisticated computer simulation models and will share methodology and results. Simulating the physical and chemical processes that could create anoxic conditions requires at a meaningful level of detail requires massive computing power and highly sophisticated models.

At this time, however, two things are noteworthy concerning the general issue of anoxia risks:

  1. Only if iron fertilization were conducted on a massive scale for prolonged periods (i.e., entire oceans continuously fertilized for decades) would a risk of anoxia emerge; and
  2. There is absolutely no possibility that even prolonged and large iron fertilization applications would create anoxic conditions in deep waters.

Would Iron Fertilization Increase Emissions of Methane and Other Greenhouse Gases?

Several observers have noted that some greenhouse gases, notably methane, may be increased by decomposition of phytoplankton created by iron fertilization. If anoxic conditions are not created, however, methane would not be produced.
Institutional Issues

Should private entities have a role in development of iron fertilization, or should participation be restricted to normal channels of research?

GreenSea believes there are several strong arguments for participation of private entities in the development of iron fertilization. Specifically:

  • Conventional oceanographic research funding is limited and iron fertilization experiments are expensive, “crowding out” other research. So the development of iron fertilization has been marked by long delays between experiments, even if the results of previous experiments have been very successful;
  • Iron fertilization is controversial, which discourages government participation;
  • Demonstrations of forest and soil management and other unconventional carbon management approaches funded by corporations have created useful data that has been useful in drafting laws and guidelines.

Will the motivation to generate carbon credits foster a series of irresponsible experiments?

No. In order for any type of pollution credit to be of any practical use, the credits must be formally accepted by environmental regulatory bodies as applicable against the claimant’s obligations to control emissions. In the case of carbon offsets, the environmental regulators will include international, national, and state/provincial authorities.

For the international community of environmental regulation to accept carbon offsets produced by iron fertilization, claimants must demonstrate, in exhaustive reviews, that such credits are credible and produced using a responsible system.

No one is likely to conduct commercial-scale iron fertilization in advance of the regulatory acceptance of such credits because well-managed applications of iron fertilizers are simply too expensive.