Ocean fertilization

The marine food chain is based on photosynthesis by marine phytoplankton that combine carbon with inorganic nutrients to produce organic matter. Production is limited by the availability of nutrients, most commonly nitrogen or iron. Numerous experiments have demonstrated how iron fertilization can increase phytoplankton productivity. Nitrogen is a limiting nutrient over much of the ocean and can be supplied from various 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. Oceanic carbon naturally cycles between the surface and the deep via two "pumps" of similar scale. The "solubility" pump is driven by ocean circulation and the solubility of CO2 in seawater. The "biological" pump is driven by phytoplankton and subsequent settling of detrital particles or dispersion of dissolved organic carbon. The former has increased as a result of increasing atmospheric CO2 concentration. This CO2 sink is estimated to be approximately 2 GtC yr−1. The global phytoplankton population fell about 40 percent between 1950 and 2008 or about 1 percent per year. The most notable declines took place in polar waters and in the tropics. The decline is attributed to sea surface temperature increases. A separate study found that diatoms, the largest type of phytoplankton, declined more than 1 percent per year from 1998 to 2012, particularly in the North Pacific, North Indian and Equatorial Indian oceans. The decline appears to reduce pytoplankton's ability to sequester carbon in the deep ocean. Fertilization offers the prospect of both reducing the concentration of atmospheric greenhouse gases with the aim of slowing climate change and at the same time increasing fish stocks via increasing primary production. The reduction reduces the ocean's rate of carbon sequestration in the deep ocean. Each area of the ocean has a base sequestration rate on some timescale, e.g., annual. Fertilization must increase that rate, but must do so on a scale beyond the natural scale. Otherwise, fertilization changes the timing, but not the total amount sequestered. However, accelerated timing may have beneficial effects for primary production separate from those from sequestration. Biomass production inherently depletes all resources (save for sun and water). Either they must all be subject to fertilization or sequestration will eventually be limited by the one mostly slowly replenished (after some number of cycles) unless the ultimate limiting resource is sunlight and/or surface area. Generally, phosphate is the ultimate limiting nutrient. As oceanic phosphorus is depleted (via sequestration) it would have to be included in the fertilization cocktail supplied from terrestrial sources. == Approaches ==

Phytoplankton require a variety of nutrients. These include macronutrients such as nitrate and phosphate (in relatively high concentrations) and micronutrients such as iron and zinc (in much smaller quantities). Nutrient requirements vary across phylogenetic groups (e.g., diatoms require silicon) but may not individually limit total biomass production. Co-limitation (among multiple nutrients) may also mean that one nutrient can partially compensate for a shortage of another. Silicon does not affect total production, but can change the timing and community structure with follow-on effects on remineralization times and subsequent mesopelagic nutrient vertical distribution. and has a slow natural cycle. Where phosphate is the limiting nutrient in the photic zone, addition of phosphate is expected to increase primary phytoplankton production. This technique can give 0.83 W/m2 of globally averaged negative forcing, which is sufficient to reverse the warming effect of about half the current levels of anthropogenic emissions. One water-soluble fertilizer is diammonium phosphate (DAP), , that as of 2008 had a market price of 1700/tonne−1 of phosphorus. Using that price and the C : P Redfield ratio of 106 : 1 produces a sequestration cost (excluding preparation and injection costs) of some $45 /tonne of carbon (2008), substantially less than the trading price for carbon emissions. Concentrations of macronutrients per area of ocean surface would be similar to large natural upwellings. Once exported from the surface, the carbon remains sequestered for a long time. An Australian company, Ocean Nourishment Corporation (ONC), planned to inject hundreds of tonnes of urea into the ocean, in order to boost the growth of -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. This project was criticized by many institutions, including the European Commission, due to lack of knowledge of side effects on the marine ecosystem. Macronutrient nourishment can give 0.38 W/m2 of globally averaged negative forcing, enzymes to produce ammonia. CO(NH_2)_2 + H_2O ->[urease] NH_3 + NH_2COOH NH_2COOH + H_2O -> NH_3 + H_2CO_3 The intermediate product carbamate also reacts with water to produce a total of two ammonia molecules. Another cause of concern is the sheer amount of urea needed to capture the same amount of carbon as eq. iron fertilization. The nitrogen to iron ratio in a typical algae cell is 16:0.0001, meaning that for every iron atom added to the ocean a substantial larger amount of carbon is captured compared to adding one atom of nitrogen. Scientists also emphasize that adding urea to ocean waters could reduce oxygen content and result in a rise of toxic marine algae. Pelagic pumping 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 Monitored nutrients 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 == Complications ==

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: Outright opposition 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 "Tests have shown the iron does stimulate plankton growth. But key questions remain, says Dave Siegel, a marine scientist at the University of California, Santa Barbara, who served on the NASEM panel. How much of the absorbed carbon makes it to the deep ocean is uncertain", while Wil Burns, an ocean law expert at Northwestern University 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." Efficiency 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. Thus, each atom of iron in an iron-constrained environment helps capture 1,060,000 atoms of carbon, while a nitrogen atom in a nitrogen-constrained environment would only capture 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." Algal blooms 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. Impact on fisheries 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. Ecosystem disruption 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. == Reactions ==

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 ==

International law presents some dilemmas for ocean fertilization. The United Nations Framework Convention on Climate Change (UNFCCC 1992) has accepted mitigation actions. Law of the sea 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. == Solar radiation management ==

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. == See also ==