Ocean fertilization

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A visualization of bloom populations in the North Atlantic and North Pacific oceans from March 2003 to October 2006. The blue areas are nutrient deficient. Green to yellow show blooms fed by dust blown from nearby landmasses.[1]

Ocean fertilization or ocean nourishment is a type of climate engineering based on the purposeful introduction of nutrients to the upper ocean[2] to increase marine food production[3] and to remove carbon dioxide from the atmosphere. A number of techniques, including fertilization by iron, urea and phosphorus have been proposed. There has been commercial interest in using these techniques to reduce carbon dioxide concentrations.



In 2000 and 2004, comparable amounts of iron sulfate were discharged from the EisenEx. 10 to 20 percent of the algal bloom died off and sank to the sea floor.


LOHAFEX was an experiment initiated by the German Federal Ministry of Research and carried out by the German Alfred Wegener Institute (AWI) 2009 to study ocean fertilization in the South Atlantic. It was also an Indo-German cooperation project.[4]

As part of the experiment, the German research vessel Polarstern deposited 6 tons of iron in the form of ferrous sulfate in an area of 300 square kilometers. It was expected that the iron sulphate would distribute through the upper 15 metres (49 ft) of water and trigger an algal bloom. A significant part of the carbon dioxide dissolved in sea water would then be bound by the emerging bloom and sink to the ocean floor.

The ship left Cape Town, South Africa 7 January 2009. The expedition ended after 70 days on 17 March 2009 in Punta Arenas, Chile.

The Federal Environment Ministry called for a halt to the experiment, partly because environmentalists feared damage to marine plants. Others feared long-term effects that would not be detectable during short-term observation[5] or that this would encourage large-scale ecosystem manipulation of ecosystems.[6][7]

Haida Gwaii project[edit]

In July 2012, the Haida Salmon Restoration Corporation dispersed 100 short tons (91 t) of iron sulphate dust into the Pacific Ocean several hundred miles west of the islands of Haida Gwaii. The Old Massett Village Council financed this project as a salmon enhancement project with $2.5 million in village funds.[8] The concept was that the formerly iron-deficient waters would produce more phytoplankton that would in turn serve as a "pasture" to feed salmon. Then- CEO Russ George hoped to sell carbon offsets to recover the costs. The project was plagued by charges of unscientific procedures and recklessness. George contended that 100 tons of iron is negligible compared to what naturally enters the ocean.[9]

Some environmentalists called the dumping a "blatant violation" of two international moratoriums.[8][10] George said that the Old Massett Village Council and its lawyers approved the effort and at least seven Canadian agencies were aware of it.[9]

The 2013 salmon runs defied all expectations, more than quadrupling, from 50 million to 226 million fish.[11]

On 15 July 2014, the oceanographic scientific data that has been gathered during the project were made publicly available under the ODbL license.[12]

Techniques and motivation[edit]

sequestration in the ocean

The marine food chain is based on photosynthesis by marine phytoplankton which combine carbon with inorganic nutrients to produce organic matter. The production of organic matter is limited in general by the availability of nutrients, most commonly nitrogen or iron. Numerous experiments[13] have been carried out demonstrating how iron fertilization can increase phytoplankton productivity. Nitrogen is a limiting nutrient over much of the ocean and can be supplied from a number of sources including fixation by cyanobacteria. Carbon-to-iron ratios in phytoplankton are much larger than carbon-to-nitrogen or carbon-to-phosphorus ratios, so iron has the highest potential for sequestration per unit mass added.

Ocean fertilization offers the prospect of both reducing the concentration of atmospheric greenhouse gases with the aim of avoiding dangerous climate change and at the same time increasing the sustainable fish stocks. It promises to do this by increasing the ocean primary production.

Ocean fertilization may be a way of creating low cost protein in sufficient quantity to supply the needs of the additional two billion people expected to populate the earth before the population stabilizes at values near eight billion.[citation needed] While manipulation of the land ecosystem in support of agriculture for the benefit of humans has long been accepted it is a new concept to enhance the large scale ocean productivity and so creates some apprehension.

Iron fertilization[edit]

Main article: Iron fertilization

In large areas of ocean, there are very few phytoplankton, despite there being high levels of nutrients. John Martin, director of the Moss Landing Marine Laboratories, came up with a hypothesis that the low levels of phytoplankton in these regions are due to a lack of iron. To test this hypothesis (known as the Iron Hypothesis) he arranged an experiment where samples of clean water from Antarctica were collected. To some of these samples iron was added but not to others. They were then left for several days and the phytoplankton in the samples with added iron grew much more than in the untreated samples. This led Martin to speculate that increased iron concentrations in the oceans could partly explain past ice ages.[14] This experiment was followed up by a much larger field experiment (IRONEX I) where 445 kg of iron was added to a patch of ocean near the Galápagos Islands. The levels of phytoplankton increased three times in the area where the iron had been added.[15] The success of this experiment and others has led to proposals to use this technique to remove carbon dioxide from the atmosphere on a commercial basis.[16]

Sperm whales act as agents of iron fertilisation when they transport iron from the deep ocean to the surface during prey consumption and defecation. Sperm whales have been shown to increase the levels of primary production and carbon export to the deep ocean by depositing iron rich faeces into surface waters of the Southern Ocean. The iron rich faeces causes phytoplankton to grow and take up more carbon from the atmosphere. When the phytoplankton dies, it sinks to the deep ocean and takes the atmospheric carbon with it. By reducing the abundance of sperm whales in the Southern Ocean, whaling has resulted in an extra 2 million tonnes of carbon remaining in the atmosphere each year.[17]

Cost of iron fertilization[edit]

The cost of distributing iron over large area of ocean is large compared with the value of the expected carbon credits.[18]

Phosphorus fertilization[edit]

Where phosphate is the limiting nutrient in the photic zone, addition of phosphate is expected to support an increase in primary production. This technique can give 0.83W/m2 of globally averaged negative forcing,[19] which is sufficient to reverse the warming effect of about half the current levels of anthropogenic CO
emissions. It is notable, however, that CO
levels will have risen by the time this could be achieved.

Nitrogen fertilization[edit]

This technique (proposed by Ian Jones) suggests fertilizing the ocean with urea, a nitrogen rich substance, to encourage phytoplankton growth.[20] and has also been considered by Karl.[21] Doses of macronutrients per area of ocean surface would be typical of nutrient concentration of large upwellings. The carbon, once exported from the surface layer of the ocean, remains sequestered for a long time.[22]

An Australian company, Ocean Nourishment Corporation (ONC), plans to inject hundreds of tonnes of urea into the ocean, in order to boost the growth of CO
-absorbing phytoplankton, as a way to combat climate change. In 2007, Sydney-based ONC completed an experiment involving one tonne of nitrogen in the Sulu Sea off the Philippines.[23]

Nitrogen fertilization is a form of CDR, carbon dioxide removal from the atmosphere. To be put into practice the technology needs to win a social licence.[24] Macronutrient nourishment can give 0.38W/m2 of globally averaged negative forcing,[19] which is sufficient to reverse the warming effect of current levels of around a quarter of anthropogenic CO


The Ocean Nourishment Corporation has claimed that “One Ocean Nourishment plant will remove approximately 5-8 million tonnes of CO2 from the atmosphere for each year of operation, equivalent to offsetting annual emissions from a typical 1200 MW coal-fired power station or the short-term sequestration from one million hectares of new growth forest”.[25]

The cost of ocean Nourishment[edit]

The two dominant costs in Ocean Nourishment are manufacturing the reactive nitrogen and the delivery of the nutrients to the photic zone.[26]



Algal cell chemical composition is 106 carbon: 16 nitrogen: 1 phosphorus: 0.0001 iron atoms. In other words, for each atom of iron there are 1060000 atoms of carbon are captured, however for one nitrogen atom only 6 atoms of carbon are captured.[27] Experimental iron fertilisation in HNLC regions have been supplied with excess iron which cannot be utilized before it is scavenged. Thus the organic carbon produced was much less than it would be if the ratio of atoms above were achieved. Only a fraction of the available nitrogen (because of iron scavenging) is drawn down. In culture bottle studies of oligotrophic water, adding nitrogen and phosphorus, can draw down considerably more nitrogen per dosing. The export production is only a small percentage of the new primary production and in the case of iron fertilization, the scavenging of iron means that regenerative production is small. With macronutrient fertilisation regenerative production is expected to be large and supportive of larger total export. A paper by Lawrence [28] examines the various losses that reduce the efficiency of ocean nourishment.

Limited impact on fisheries[edit]

Adding urea to the ocean can cause blooms of phytoplankton that is source of food of zooplankton and in turn feed for fish. This is in turn expected to increase the sustainable fish catch.[29] However, if cyanobactaria and dinoflagellates dominate phytoplankton assemblages that are considered poor quality food for fish then the increase in fish quantity may not be as large as expected.[30]


Many locations, such as the Tubbataha Reef in the Sulu Sea, supports high marine biodiversity [31] and nitrogen loading in coral reef areas can lead to community shifts towards algal overgrowth of corals and ecosystem disruption.[32] Care will be needed to avoid fertilizing upstream of sensitive areas of ocean.

Volcanic ash as a nutrient source[edit]

Volcanic ash adds nutrients to the surface ocean. This is most apparent in areas that are nutrient limited. Considerable research has been done on the effects of anthropogenic and eolian iron addition to the ocean surface, but some research suggests that nutrient-limited areas benefit most from a combination of nutrients provided by anthropogenic, eolian, and volcanic deposition.[33] Some nutrient-limited oceanic areas are limited in more than one nutrient, so the biological community is more likely to thrive from adding multiple nutrients like P, N, and Fe, than if only Fe were added to the system. Volcanic ash has the potential to add these multiple nutrients to the system, allowing the biota to thrive, but excess metal ions can be harmful to systems limited by nutrients. The positive impacts of volcanic ash deposition are potentially outweighed by their potential to do harm.[citation needed]

There is clear evidence for the presence of as much as 45 percent by weight of ash in some deep marine sediments.[34][35] In the Pacific Ocean, the largest ocean basin covering half of the Earth's surface area, estimates have shown that (on a millennial-scale) the atmospheric deposition of air-fall volcanic ash has been as high as the deposition of desert dust.[36] This indicates the potential of volcanic ash being a significant source of iron in the surface ocean.

In August 2008 an eruption in the Aleutian Islands, Alaska, deposited ash in the nutrient limited North-East Pacific. There is strong evidence that this ash and iron deposition resulted in one of the largest phytoplankton blooms observed in the subarctic.[37]

Ocean nourishment and International Law[edit]

From the perspective of international law there are some dilemmas around iron, urea, or phosphorus fertilization of the ocean. On one hand the United Nations Framework Convention on Climate Change (UNFCCC 1992) has accepted mitigation actions.[citation needed] On the other hand, the UNFCCC and its revisions currently only recognise forestation and reforestation projects as carbon sinks[citation needed] and international law protects and preserves the marine environment.[citation needed] Some commercial companies like Climos and GreenSea Ventures, and the Australian-based Ocean Nourishment Corporation, plan to engage in urea and iron fertilization projects. These companies invite green co-sponsors to finance their activities in return for provision of carbon credits to offset investors’ CO2 emissions.[38]

In June 2007 the London Dumping Convention issued a statement of concern noting 'the potential for large scale ocean iron fertilization to have negative impacts on the marine environment and human health'.[39] but the term 'large scale' was not defined. It is believed that large scale would refer to operations on the scale then planned by Planktos.[citation needed] Planktos is a USA-based company, which abandoned its plans to conduct 6 iron fertilzation cruises from 2007 to 2009, each of which would have dissolved up to 100 tons of iron over a 10,000 km2 area of ocean. The plans were abandoned because their ship Weatherbird II was refused entry to the port of Las Palmas in the Canary Islands where it was to take on provisions and scientific equipment.[40]

In 2008, the London Convention/ London Protocol noted in resolution LC-LP.1 (2008) that that knowledge on the effectiveness and potential environmental impacts of ocean fertilization is currently insufficient to justify activities other than legitimate scientific research. This non-binding resolution states that ocean fertilization activities, other than legitimate scientific research, "should be considered as contrary to the aims of the Convention and Protocol and do not currently qualify for any exemption from the definition of dumping".[41]

Working Group III of the United Nations Intergovernmental Panel on Climate Change examined ocean fertilization methods in its fourth assessment report and noted that the field-study estimates of the amount of carbon removed per ton of iron is probably over-estimated by current studies and that other potential adverse effects have not yet been fully studied.[42]

Law of sea issues[edit]

According to United Nations Convention on the Law of the Sea(LOSC 1982), all states are obliged to take individually and jointly all measures necessary to prevent, reduce and control pollution of the marine environment, to prohibit the transfer, either directly or indirectly, of damage or hazards from one area to another, and to prohibit the transformation of one type pollution to another. However, it is not proven that iron would act as a pollutant, and by reducing the effect of high levels of CO2 may act in the opposite way.[43]

Solar radiation management[edit]

As well as carbon sequestration, ocean fertilization may also create sulfate aerosols which reflect sunlight and modify the Earth's albedo, this creating a cooling effect which reduces some of the effects of climate change. Enhancing the natural sulfur cycle in the Southern Ocean[44] by fertilizing a small portion with iron in order to enhance dimethyl sulfide production and cloud reflectivity may achieve this. The goal is to slow Antarctic ice from melting and raising sea level.[45][46]

See also[edit]


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