Ocean fertilization

Type of climate engineering

information on ocean fertilization schemes with iron in particular

Ocean fertilization or ocean nourishment is a type of technology for carbon dioxide removal from the ocean based on the purposeful introduction of plant nutrients to the upper ocean to increase marine food production and to remove carbon dioxide from the atmosphere. Ocean nutrient fertilization, for example iron fertilization, could stimulate photosynthesis in phytoplankton. The phytoplankton would convert the ocean's dissolved carbon dioxide into carbohydrate, some of which would sink into the deeper ocean before oxidizing. More than a dozen open sea experiments confirmed that adding iron to the ocean increases photosynthesis in phytoplankton by up to 30 times. This is one of the more well researched carbon dioxide removal (CDR) approaches, however this approach would only sequester carbon on a timescale of 10 100 years dependent on ocean mixing times. While surface ocean acidity may decrease as a result of nutrient fertilization, when the sinking organic matter remineralizes, deep ocean acidity will increase. A 2021 report on CDR indicates that there is medium high confidence that the technique could be efficient and scalable at low cost, with medium environmental risks. One of the key risks of nutrient fertilization is nutrient robbing, a process by which excess nutrients used in one location for enhanced primary productivity, as in a fertilization context, are then unavailable for normal productivity downstream. This could result in ecosystem impacts far outside the original site of fertilization.

Local wave power could be used to pump nutrient rich water from hundred metre plus depths to the euphotic zone. However, deep water concentrations of dissolved CO2 could be returned to the atmosphere. Some oceanic areas are comparably limited in more than one nutrient, so fertilization regimes that includes all limited nutrients is more likely to succeed. Volcanic ash supplies multiple nutrients to the system, but excess metal ions can be harmful. The positive impacts of volcanic ash deposition are potentially outweighed by their potential to do harm. Clear evidence documents that ash can be as much as 45 percent by weight in some deep marine sediments. In the Pacific Ocean estimates claim that (on a millennial scale) the atmospheric deposition of air fall volcanic ash was as high as the deposition of desert dust. This indicates the potential of volcanic ash as a significant iron source. In August 2008 the Kasatochi volcanic eruption in the Aleutian Islands, Alaska, deposited ash in the nutrient limited northeast Pacific. This ash (including iron) resulted in one of the largest phytoplankton blooms observed in the subarctic. Fisheries scientists in Canada linked increased oceanic productivity from the volcanic iron to subsequent record returns of salmon in the Fraser River two years later

The approach advocated by Ocean Nutrition Corporation is to limit the distribution of added nutrients to allow phytoplankton concentrations to rise only to the values seen in upwelling regions (5–10 mg Chl /m3). Maintaining healthy phytoplankton levels is claimed to avoid harmful algal blooms and oxygen depletion. Chlorophyll concentration is an easily measured proxy for phytoplankton concentration. The company stated that values of approximately 4 mg Chl/m3 meet this requirement. SS

While manipulation of the land ecosystem in support of agriculture for the benefit of humans has long been accepted (despite its side effects), directly enhancing ocean productivity has not. Among the reasons are:

According to Lisa Speer of the Natural Resources Defense Council, "There is a limited amount of money, of time, that we have to deal with this problem The worst possible thing we could do for climate change technologies would be to invest in something that doesn't work and that has big impacts that we don't anticipate." In Science, Warren Cornwall mentions "Wil Burns, an ocean law expert at Northwestern University" who declares that " making iron fertilization a research priority is "barking mad" since " a recent survey of 13 past fertilization experiments found only one that increased carbon levels deep in the ocean."

Algal cell chemical composition is often assumed to respect a ratio where atoms are 106 carbon: 16 nitrogen: 1 phosphorus (Redfield ratio): 0.0001 iron. In other words, each atom of iron helps capture 1,060,000 atoms of carbon, while one nitrogen atom only 6. In large areas of the ocean, such organic growth (and hence nitrogen fixation) is thought to be limited by the lack of iron rather than nitrogen, although direct measures are hard. In addition, the efficiency of carbon sequestration through ocean fertilisation is heavily influenced by factors such as changes in stoichiometric ratios and gas exchange make accurately predicting the effectiveness of ocean feralization projects. Fertilisation also does not create a permanent carbon sink. "Ocean fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition may have greater long term potential than iron or nitrogen fertilisation."

Toxic algal blooms are common in coastal areas. Fertilization could trigger such blooms. Chronic fertilization could risk the creation of dead zones, such as the one in the Gulf of Mexico.

Adding urea to the ocean can cause phytoplankton blooms that serve as a food source for zooplankton and in turn feed for fish. This may increase fish catches. However, if cyanobacteria and dinoflagellates dominate phytoplankton assemblages that are considered poor quality food for fish then the increase in fish quantity may not be large. Some evidence links iron fertilization from volcanic eruptions to increased fisheries production. Krill populations have declined dramatically since whaling began.

Many locations, such as the Tubbataha Reef in the Sulu Sea, support high marine biodiversity. Nitrogen or other nutrient loading in coral reef areas can lead to community shifts towards algal overgrowth of corals and ecosystem disruption, implying that fertilization must be restricted to areas in which vulnerable populations are not put at risk. As the phytoplankton descend the water column, they decay, consuming oxygen and producing greenhouse gases methane and nitrous oxide. Plankton rich surface waters could warm the surface layer, affecting circulation patterns.

In 2007 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 was probably over estimated and that potential adverse effects had not been fully studied. 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', but did not define 'large scale'. It is believed that the definition would include operations. In 2008, the London Convention/London Protocol noted in resolution LC LP.1 that knowledge on the effectiveness and potential environmental impacts of ocean fertilization was insufficient to justify activities other than research. This non binding resolution stated that fertilization, other than 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". In May 2008, at the Convention on Biological Diversity, 191 nations called for a ban on ocean fertilization until scientists better understand the implications. In August 2018, Germany banned the sale of ocean seeding as carbon sequestration system while the matter was under discussion at EU and EASAC levels.

International law presents some dilemmas for ocean fertilization. The United Nations Framework Convention on Climate Change (UNFCCC 1992) has accepted mitigation actions.

According to United Nations Convention on the Law of the Sea (LOSC 1982), all states are obliged to take all measures necessary to prevent, reduce and control pollution of the marine environment, to prohibit the transfer of damage or hazards from one area to another and to prohibit the transformation of one type pollution to another. How this relates to fertilization is undetermined.

Fertilization may create sulfate aerosols that reflect sunlight, modifying the Earth's albedo, creating a cooling effect that reduces some of the effects of climate change. Enhancing the natural sulfur cycle in the Southern Ocean by fertilizing with iron in order to enhance dimethyl sulfide production and cloud reflectivity may achieve this.