iron fertilization

Ocean iron fertilization is an example of a geoengineering technique that involves intentional introduction of iron-rich deposits into oceans, and is aimed to enhance biological productivity of organisms in ocean waters in order to increase carbon dioxide ({{CO2|link=yes}}) uptake from the atmosphere, possibly resulting in mitigating its global warming effects.{{Cite news |last=Traufetter |first=Gerald |date=2009-01-02 |title=Cold Carbon Sink: Slowing Global Warming with Antarctic Iron |work=Spiegel Online |url=http://www.spiegel.de/international/world/cold-carbon-sink-slowing-global-warming-with-antarctic-iron-a-599213.html#ref=rss |access-date=2018-11-18}}{{Cite journal |last1=Jin |first1=X. |last2=Gruber |first2=N. |last3=Frenzel |first3=H. |last4=Doney |first4=S. C. |last5=McWilliams |first5=J. C. |date=2008-03-18 |title=The impact on atmospheric {{CO2}} of iron fertilization induced changes in the ocean's biological pump |journal=Biogeosciences |language=en |volume=5 |issue=2 |pages=385–406 |bibcode=2008BGeo....5..385J |doi=10.5194/bg-5-385-2008 |issn=1726-4170 |doi-access=free|hdl=1912/2129 |hdl-access=free }}{{Cite journal |last=Monastersky |first=Richard |date=September 30, 1995 |title=Iron versus the Greenhouse: Oceanographers cautiously explore a global warming therapy |url=http://www-formal.stanford.edu/pub/jmc/progress/iron/iron.html |journal=Science News |volume=148 |pages=220 |doi=10.2307/4018225 |jstor=4018225}}{{Cite journal |last1=Martínez-García |first1=Alfredo |last2=Sigman |first2=Daniel M. |last3=Ren |first3=Haojia |last4=Anderson |first4=Robert F. |last5=Straub |first5=Marietta |last6=Hodell |first6=David A. |last7=Jaccard |first7=Samuel L. |last8=Eglinton |first8=Timothy I. |last9=Haug |first9=Gerald H. |date=2014-03-21 |title=Iron Fertilization of the Subantarctic Ocean During the Last Ice Age |journal=Science |language=en |volume=343 |issue=6177 |pages=1347–1350 |bibcode=2014Sci...343.1347M |doi=10.1126/science.1246848 |issn=0036-8075 |pmid=24653031 |s2cid=206552831}}{{Cite journal |last1=Pasquier |first1=Benoît |last2=Holzer |first2=Mark |date=2018-08-16 |title=Iron fertilization efficiency and the number of past and future regenerations of iron in the ocean |journal=Biogeosciences Discussions |language=en |volume=15 |issue=23 |pages=7177–7203 |bibcode=2018AGUFMGC23G1277P |doi=10.5194/bg-2018-379 |issn=1726-4170 |s2cid=133851021 |doi-access=free }} Iron is a trace element in the ocean and its presence is vital for photosynthesis in plants, and in particular phytoplanktons, as it has been shown that iron deficiency can limit ocean productivity and phytoplankton growth.{{Cite journal |last1=Boyd |first1=Philip W. |last2=Watson |first2=Andrew J. |last3=Law |first3=Cliff S. |last4=Abraham |first4=Edward R. |last5=Trull |first5=Thomas |last6=Murdoch |first6=Rob |last7=Bakker |first7=Dorothee C. E. |last8=Bowie |first8=Andrew R. |last9=Buesseler |first9=K. O. |date=October 2000 |title=A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization |journal=Nature |language=En |volume=407 |issue=6805 |pages=695–702 |bibcode=2000Natur.407..695B |doi=10.1038/35037500 |issn=0028-0836 |pmid=11048709 |s2cid=4368261}} For this reason, the "iron hypothesis" was put forward by Martin in late 1980s where he suggested that changes in iron supply in iron-deficient seawater can bloom plankton growth and have a significant effect on the concentration of atmospheric carbon dioxide by altering rates of carbon sequestration.{{Cite journal |last1=Boyd |first1=P. W. |last2=Jickells |first2=T. |last3=Law |first3=C. S. |last4=Blain |first4=S. |last5=Boyle |first5=E. A. |last6=Buesseler |first6=K. O. |last7=Coale |first7=K. H. |last8=Cullen |first8=J. J. |last9=de Baar |first9=H. J. W. |date=2007-02-02 |title=Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions |url=https://www.science.org/doi/10.1126/science.1131669 |journal=Science |volume=315 |issue=5812 |pages=612–617 |doi=10.1126/science.1131669|pmid=17272712 |bibcode=2007Sci...315..612B }}{{Cite web |date=2001-07-10 |title=John Martin |url=https://earthobservatory.nasa.gov/Features/Martin |access-date=2018-11-19 |website=earthobservatory.nasa.gov |language=en}} In fact, fertilization is an important process that occurs naturally in the ocean waters. For instance, upwellings of ocean currents can bring nutrient-rich sediments to the surface.{{Cite journal |last1=Ian |first1=Salter |last2=Ralf |first2=Schiebel |last3=Patrizia |first3=Ziveri |last4=Aurore |first4=Movellan |last5=S. |first5=Lampitt, Richard |last6=A. |first6=Wolff, George |date=2015-02-23 |title=Carbonate counter pump stimulated by natural iron fertilization in the Southern Ocean |url=http://epic.awi.de/40452/ |language=de-DE |access-date=2018-11-19 |website=epic.awi.de}} Another example is through transfer of iron-rich minerals, dust, and volcanic ash over long distances by rivers, glaciers, or wind.{{Cite web |date=2007-11-29 |title=Text taken from a draft review, "The role of grazing in structuring Southern Ocean pelagic ecosystems and biogeochemical cycles" |url=http://www.tyndall.ac.uk/events/past_events/ocean_fert.pdf |url-status=live |archive-url=https://web.archive.org/web/20071129123537/http://www.tyndall.ac.uk/events/past_events/ocean_fert.pdf |archive-date=2007-11-29 |access-date=2018-11-19 |website=Tyndall Centre}}{{Cite journal |last1=Hodson |first1=Andy |last2=Nowak |first2=Aga |last3=Sabacka |first3=Marie |last4=Jungblut |first4=Anne |last5=Navarro |first5=Francisco |last6=Pearce |first6=David |last7=Ávila-Jiménez |first7=María Luisa |last8=Convey |first8=Peter |last9=Vieira |first9=Gonçalo |date=2017-02-15 |title=Climatically sensitive transfer of iron to maritime Antarctic ecosystems by surface runoff |journal=Nature Communications |language=En |volume=8 |pages=14499 |bibcode=2017NatCo...814499H |doi=10.1038/ncomms14499 |issn=2041-1723 |pmc=5316877 |pmid=28198359}} Moreover, it has been suggested that whales can transfer iron-rich ocean dust to the surface, where planktons can take it up to grow. It has been shown that reduction in the number of sperm whales in the Southern Ocean has resulted in a 200,000 tonnes/yr decrease in the atmospheric carbon uptake, possibly due to limited phytoplankton growth.{{Cite journal |last1=Lavery |first1=Trish J. |last2=Roudnew |first2=Ben |last3=Gill |first3=Peter |last4=Seymour |first4=Justin |last5=Seuront |first5=Laurent |last6=Johnson |first6=Genevieve |last7=Mitchell |first7=James G. |last8=Smetacek |first8=Victor |date=2010-11-22 |title=Iron defecation by sperm whales stimulates carbon export in the Southern Ocean |journal=Proceedings of the Royal Society of London B: Biological Sciences |language=en |volume=277 |issue=1699 |pages=3527–3531 |doi=10.1098/rspb.2010.0863 |issn=0962-8452 |pmc=2982231 |pmid=20554546}}

File:Phytoplankton_bloom_off_the_coast_of_Scotland.jpg bloom in the North Sea off the coast of eastern Scotland]]

Phytoplankton is photosynthetic: it needs sunlight and nutrients to grow, and takes up carbon dioxide in the process. Plankton can take up and sequester atmospheric carbon through generating calcium or silicon-carbonate skeletons. When these organisms die they sink to the ocean floor where their carbonate skeletons can form a major component of the carbon-rich deep sea precipitation, thousands of meters below plankton blooms, known as marine snow.{{Cite journal |last1=J. |first1=Brooks |last2=K. |first2=Shamberger |last3=B. |first3=Roark, E. |last4=K. |first4=Miller |last5=A. |first5=Baco-Taylor |date=February 2016 |title=Seawater Carbonate Chemistry of Deep-sea Coral Beds off the Northwestern Hawaiian Islands |journal=American Geophysical Union, Ocean Sciences Meeting |language=en |volume=2016 |pages=AH23A–03 |bibcode=2016AGUOSAH23A..03B}}{{Cite journal |last1=Laurenceau-Cornec |first1=Emmanuel C. |last2=Trull |first2=Thomas W. |last3=Davies |first3=Diana M. |last4=Rocha |first4=Christina L. De La |last5=Blain |first5=Stéphane |date=2015-02-03 |title=Phytoplankton morphology controls on marine snow sinking velocity |journal=Marine Ecology Progress Series |language=en |volume=520 |pages=35–56 |bibcode=2015MEPS..520...35L |doi=10.3354/meps11116 |issn=0171-8630 |doi-access=free}}{{Cite journal |last1=Prairie |first1=Jennifer C. |last2=Ziervogel |first2=Kai |last3=Camassa |first3=Roberto |last4=McLaughlin |first4=Richard M. |last5=White |first5=Brian L. |last6=Dewald |first6=Carolin |last7=Arnosti |first7=Carol |date=2015-10-20 |title=Delayed settling of marine snow: Effects of density gradient and particle properties and implications for carbon cycling |journal=Marine Chemistry |language=en |volume=175 |pages=28–38 |doi=10.1016/j.marchem.2015.04.006 |bibcode=2015MarCh.175...28P |issn=0304-4203 |doi-access=free}} Nonetheless, based on the definition, carbon is only considered "sequestered" when it is deposited in the ocean floor where it can be retained for millions of years. However, most of the carbon-rich biomass generated from plankton is generally consumed by other organisms (small fish, zooplankton, etc.){{Cite journal |last1=Steinberg |first1=Deborah K. |last2=Landry |first2=Michael R. |date=2017-01-03 |title=Zooplankton and the Ocean Carbon Cycle |journal=Annual Review of Marine Science |language=en |volume=9 |issue=1 |pages=413–444 |bibcode=2017ARMS....9..413S |doi=10.1146/annurev-marine-010814-015924 |issn=1941-1405 |pmid=27814033}}{{Cite journal |last1=Cavan |first1=Emma L. |last2=Henson |first2=Stephanie A. |last3=Belcher |first3=Anna |last4=Sanders |first4=Richard |date=2017-01-12 |title=Role of zooplankton in determining the efficiency of the biological carbon pump |url=https://eprints.soton.ac.uk/403842/ |journal=Biogeosciences |language=en |volume=14 |issue=1 |pages=177–186 |bibcode=2017BGeo...14..177C |doi=10.5194/bg-14-177-2017 |issn=1726-4189 |doi-access=free}} and substantial part of rest of the deposits that sink beneath plankton blooms may be re-dissolved in the water and gets transferred to the surface where it eventually returns to the atmosphere, thus, nullifying any possible intended effects regarding carbon sequestration.{{Cite journal |last1=Robinson |first1=J. |last2=Popova |first2=E. E. |last3=Yool |first3=A. |last4=Srokosz |first4=M. |last5=Lampitt |first5=R. S. |last6=Blundell |first6=J. R. |date=2014-04-11 |title=How deep is deep enough? Ocean iron fertilization and carbon sequestration in the Southern Ocean |url=http://nora.nerc.ac.uk/id/eprint/507032/1/grl51570_Robinson.pdf |journal=Geophysical Research Letters |language=en |volume=41 |issue=7 |pages=2489–2495 |bibcode=2014GeoRL..41.2489R |doi=10.1002/2013gl058799 |issn=0094-8276 |s2cid=53389222}}{{Cite journal |last1=Hauck |first1=Judith |last2=Köhler |first2=Peter |last3=Wolf-Gladrow |first3=Dieter |last4=Völker |first4=Christoph |date=2016 |title=Iron fertilisation and century-scale effects of open ocean dissolution of olivine in a simulated CO 2 removal experiment |journal=Environmental Research Letters |language=en |volume=11 |issue=2 |pages=024007 |bibcode=2016ERL....11b4007H |doi=10.1088/1748-9326/11/2/024007 |issn=1748-9326 |doi-access=free}}{{Cite journal |last1=Tremblay |first1=Luc |last2=Caparros |first2=Jocelyne |last3=Leblanc |first3=Karine |last4=Obernosterer |first4=Ingrid |date=2014 |title=Origin and fate of particulate and dissolved organic matter in a naturally iron-fertilized region of the Southern Ocean |url=https://hal-amu.archives-ouvertes.fr/hal-01234611/ |journal=Biogeosciences |language=en |volume=12 |issue=2 |page=607 |bibcode=2015BGeo...12..607T |doi=10.5194/bg-12-607-2015 |s2cid=9333764 |doi-access=free }}{{Cite journal |last1=Arrhenius |first1=Gustaf |last2=Mojzsis |first2=Stephen |last3=Atkinson |first3=A. |last4=Fielding |first4=S. |last5=Venables |first5=H. J. |last6=Waluda |first6=C. M. |last7=Achterberg |first7=E. P. |date=2016-10-10 |title=Zooplankton Gut Passage Mobilizes Lithogenic Iron for Ocean Productivity |url=http://plymsea.ac.uk/7256/1/CB2619_Zooplankton_AAM_Schmidt.pdf |journal=Current Biology |language=en |volume=26 |issue=19 |pages=2667–2673 |doi=10.1016/j.cub.2016.07.058 |issn=0960-9822 |pmid=27641768 |bibcode=2016CBio...26.2667S |s2cid=3970146}}{{Cite thesis |last=Vinay |first=Subhas, Adam |date=2017 |title=Chemical Controls on the Dissolution Kinetics of Calcite in Seawater |url=https://thesis.library.caltech.edu/10330/ |doi=10.7907/z93x84p3 |publisher=California Institute of Technology |type=phd}} Nevertheless, supporters of the idea of iron fertilization believe that carbon sequestration should be re-defined over much shorter time frames and claim that since the carbon is suspended in the deep ocean it is effectively isolated from the atmosphere for hundreds of years, and thus, carbon can be effectively sequestered.{{Cite journal |last1=Jackson |first1=R. B. |last2=Canadell |first2=J. G. |last3=Fuss |first3=S. |last4=Milne |first4=J. |last5=Nakicenovic |first5=N. |last6=Tavoni |first6=M. |date=2017 |title=Focus on negative emissions |journal=Environmental Research Letters |language=en |volume=12 |issue=11 |pages=110201 |bibcode=2017ERL....12k0201J |doi=10.1088/1748-9326/aa94ff |issn=1748-9326 |doi-access=free}}

Assuming the ideal conditions, the upper estimates for possible effects of iron fertilisation in slowing down global warming is about 0.3W/m² of averaged negative forcing which can offset roughly 15–20% of the current anthropogenic {{CO2}} emissions.{{Cite journal |last1=Lenton |first1=T. M. |last2=Vaughan |first2=N. E. |date=2009-01-28 |title=The radiative forcing potential of different climate geoengineering options |url=https://ueaeprints.uea.ac.uk/24298/1/grn_lenton_vaughan_2009.pdf |journal=Atmospheric Chemistry and Physics Discussions |volume=9 |issue=1 |pages=2559–2608 |doi=10.5194/acpd-9-2559-2009 |issn=1680-7375 |doi-access=free }}{{cite patent|country=US|number=20180217119|title=Process and method for the enhancement of sequestering atmospheric carbon through ocean iron fertilization, and method for calculating net carbon capture from said process and method|issue-date=2016-07-28}}{{Cite journal |last1=Gattuso |first1=J.-P. |last2=Magnan |first2=A. |last3=Billé |first3=R. |last4=Cheung |first4=W. W. L. |last5=Howes |first5=E. L. |last6=Joos |first6=F. |last7=Allemand |first7=D. |last8=Bopp |first8=L. |last9=Cooley |first9=S. R. |date=2015-07-03 |title=Contrasting futures for ocean and society from different anthropogenic {{CO2}} emissions scenarios |url=https://hal.sorbonne-universite.fr/hal-01176217/file/Gattuso_2015_Contrasting_futures.pdf |journal=Science |language=en |volume=349 |issue=6243 |pages=aac4722 |doi=10.1126/science.aac4722 |issn=0036-8075 |pmid=26138982 |s2cid=206639157}} This approach, which stimulates phytoplankton growth by introducing iron into nutrient-poor regions of the ocean, could be seen as a potentially easy and scalable method to reduce atmospheric {{CO2}} levels. However, while it offers a theoretical means of mitigating climate change, ocean iron fertilisation remains highly controversial and debated due to its potential negative impacts on marine ecosystems. {{Cite journal |last1=El-Jendoubi |first1=Hamdi |last2=Vázquez |first2=Saúl |last3=Calatayud |first3=Ángeles |last4=Vavpetič |first4=Primož |last5=Vogel-Mikuš |first5=Katarina |last6=Pelicon |first6=Primoz |last7=Abadía |first7=Javier |last8=Abadía |first8=Anunciación |last9=Morales |first9=Fermín |date=2014 |title=The effects of foliar fertilization with iron sulfate in chlorotic leaves are limited to the treated area. A study with peach trees (Prunus persica L. Batsch) grown in the field and sugar beet (Beta vulgaris L.) grown in hydroponics |journal=Frontiers in Plant Science |language=en |volume=5 |pages=2 |doi=10.3389/fpls.2014.00002 |issn=1664-462X |pmc=3895801 |pmid=24478782 |doi-access=free}}{{Cite journal |last1=Yoon |first1=Joo-Eun |last2=Yoo |first2=Kyu-Cheul |last3=Macdonald |first3=Alison M. |last4=Yoon |first4=Ho-Il |last5=Park |first5=Ki-Tae |last6=Yang |first6=Eun Jin |last7=Kim |first7=Hyun-Cheol |last8=Lee |first8=Jae Il |last9=Lee |first9=Min Kyung |date=2018-10-05 |title=Reviews and syntheses: Ocean iron fertilization experiments – past, present, and future looking to a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) project |journal=Biogeosciences |volume=15 |issue=19 |pages=5847–5889 |bibcode=2018BGeo...15.5847Y |doi=10.5194/bg-15-5847-2018 |issn=1726-4189 |doi-access=free}}{{Cite journal |last1=Gim |first1=Byeong-Mo |last2=Hong |first2=Seongjin |last3=Lee |first3=Jung-Suk |last4=Kim |first4=Nam-Hyun |last5=Kwon |first5=Eun-Mi |last6=Gil |first6=Joon-Woo |last7=Lim |first7=Hyun-Hwa |last8=Jeon |first8=Eui-Chan |last9=Khim |first9=Jong Seong |date=2018-10-01 |title=Potential ecotoxicological effects of elevated bicarbonate ion concentrations on marine organisms |journal=Environmental Pollution |language=en |volume=241 |pages=194–199 |doi=10.1016/j.envpol.2018.05.057 |issn=0269-7491 |pmid=29807279 |bibcode=2018EPoll.241..194G |s2cid=44160652}}

Research in this field suggests that introducing large amounts of iron-rich dust into the ocean can significantly disturb the ocean's nutrient balance. These disruptions can create serious issues within the food chain, threatening the survival of marine organisms that rely on stable nutrient cycles. {{Cite news |last=Traufetter |first=Gerald |date=2009-01-02 |title=Cold Carbon Sink: Slowing Global Warming with Antarctic Iron |url=http://www.spiegel.de/international/world/cold-carbon-sink-slowing-global-warming-with-antarctic-iron-a-599213.html#ref=rss |access-date=2018-11-19 |work=Spiegel Online}}{{Cite web |date=2009-08-03 |title=Reuters AlertNet - RPT-FEATURE-Scientists urge caution in ocean-{{CO2}} capture schemes |url=http://www.alertnet.org/thenews/newsdesk/SP39844.htm |archive-url=https://web.archive.org/web/20090803085453/http://www.alertnet.org/thenews/newsdesk/SP39844.htm |archive-date=2009-08-03 |access-date=2018-11-19}}{{Cite news |date=2007-06-27 |title=WWF condemns Planktos Inc. iron-seeding plan in the Galapagos |url=http://www.geoengineeringmonitor.org/2007/06/wwf-condemns-planktos-inc-iron-seeding-plan-in-the-galapagos/ |access-date=2018-11-19 |work=Geoengineering Monitor |language=en-US}}{{Cite journal |last1=Glibert |first1=Patricia |author-link1=Patricia Glibert |last2=Anderson |first2=Donald |last3=Gentien |first3=Patrick |last4=Granéli |first4=Edna |last5=Sellner |first5=Kevin |date=June 2005 |title=The Global, Complex Phenomena of Harmful Algal Blooms {{!}} Oceanography |url=https://tos.org/oceanography/article/the-global-complex-phenomena-of-harmful-algal-blooms |journal=Oceanography |volume=18 |issue=2 |pages=136–147 |doi=10.5670/oceanog.2005.49 |access-date=2018-11-19 |doi-access=free |hdl-access=free |hdl=1912/2790}}{{Cite journal |last1=Moore |first1=J.Keith |last2=Doney |first2=Scott C |last3=Glover |first3=David M |last4=Fung |first4=Inez Y |date=2001 |title=Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean |url=https://escholarship.org/uc/item/17x1c4nh |journal=Deep Sea Research Part II: Topical Studies in Oceanography |language=en |volume=49 |issue=1–3 |pages=463–507 |bibcode=2001DSRII..49..463M |citeseerx=10.1.1.210.1108 |doi=10.1016/S0967-0645(01)00109-6 |issn=0967-0645}}{{Cite journal |last1=Trick |first1=Charles G. |last2=Bill |first2=Brian D. |last3=Cochlan |first3=William P. |last4=Wells |first4=Mark L. |last5=Trainer |first5=Vera L. |last6=Pickell |first6=Lisa D. |date=2010-03-30 |title=Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas |journal=Proceedings of the National Academy of Sciences |language=en |volume=107 |issue=13 |pages=5887–5892 |bibcode=2010PNAS..107.5887T |doi=10.1073/pnas.0910579107 |issn=0027-8424 |pmc=2851856 |pmid=20231473 |doi-access=free}}{{Cite journal |last1=Fripiat |first1=F. |last2=Elskens |first2=M. |last3=Trull |first3=T. W. |last4=Blain |first4=S. |last5=Cavagna |first5=A. -J. |last6=Fernandez |first6=C. |last7=Fonseca-Batista |first7=D. |last8=Planchon |first8=F. |last9=Raimbault |first9=P. |date=November 2015 |title=Significant mixed layer nitrification in a natural iron-fertilized bloom of the Southern Ocean |url=http://ecite.utas.edu.au/106055 |journal=Global Biogeochemical Cycles |language=en |volume=29 |issue=11 |pages=1929–1943 |bibcode=2015GBioC..29.1929F |doi=10.1002/2014gb005051 |issn=0886-6236 |doi-access=free}} Excessive iron may also alter the structure of plankton communities, potentially favouring certain species over others, thereby reducing the diversity vital for a healthy marine ecosystem. {{Cite journal |last1=Blain |first1=Stéphane |last2=Quéguiner |first2=Bernard |last3=Armand |first3=Leanne |last4=Belviso |first4=Sauveur |last5=Bombled |first5=Bruno |last6=Bopp |first6=Laurent |last7=Bowie |first7=Andrew |last8=Brunet |first8=Christian |last9=Brussaard |first9=Corina |last10=Carlotti |first10=François |last11=Christaki |first11=Urania |last12=Corbière |first12=Antoine |last13=Durand |first13=Isabelle |last14=Ebersbach |first14=Frederike |last15=Fuda |first15=Jean-Luc |date=2007-04-26 |title=Effect of natural iron fertilization on carbon sequestration in the Southern Ocean |url=https://pubmed.ncbi.nlm.nih.gov/17460670/ |journal=Nature |volume=446 |issue=7139 |pages=1070–1074 |doi=10.1038/nature05700 |issn=1476-4687 |pmid=17460670|bibcode=2007Natur.446.1070B }} Moreover, iron fertilisation can trigger expansive phytoplankton blooms, which, as they decompose, could create hypoxic or anoxic zones in the ocean, posing severe risks to marine life and biodiversity. {{Cite journal |last1=Yarimizu |first1=Kyoko |last2=Cruz-López |first2=Ricardo |last3=Carrano |first3=Carl J. |date=2018-06-05 |title=Iron and Harmful Algae Blooms: Potential Algal-Bacterial Mutualism Between Lingulodinium polyedrum and Marinobacter algicola |journal=Frontiers in Marine Science |language=English |volume=5 |page=180 |doi=10.3389/fmars.2018.00180 |doi-access=free |bibcode=2018FrMaS...5..180Y |issn=2296-7745}} In some cases, iron fertilisation has been linked to harmful algal blooms, which can produce toxins detrimental to marine organisms and humans. {{Cite journal |last1=Trick |first1=Charles G |last2=Bill |first2=Brian D |last3=Cochlan |first3=William P |last4=Wells |first4=Mark L |last5=Trainer |first5=Vera L |last6=Pickell |first6=Lisa D |date=2010-03-15 |title=Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=107 |issue=13 |pages=5887–5892 |doi=10.1073/pnas.0910579107 |doi-access=free |pmid=20231473 |pmc=2851856 |bibcode=2010PNAS..107.5887T }} For example, trials in the Southern Ocean, including the SOFeX experiments, demonstrated that iron fertilisation can lead to the rapid growth of harmful algae, with potential consequences for local ecosystems and food chains. {{Cite journal |last1=Williamson |first1=Phillip |last2=Wallace |first2=Douglas W.R. |last3=Law |first3=Cliff S. |last4=Boyd |first4=Philip W. |last5=Collos |first5=Yves |last6=Croot |first6=Peter |last7=Denman |first7=Ken |last8=Riebesell |first8=Ulf |last9=Takeda |first9=Shigenobu |last10=Vivian |first10=Chris |date=November 2012 |title=Ocean fertilization for geoengineering: A review of effectiveness, environmental impacts and emerging governance |url=https://linkinghub.elsevier.com/retrieve/pii/S095758201200119X |journal=Process Safety and Environmental Protection |language=en |volume=90 |issue=6 |pages=475–488 |doi=10.1016/j.psep.2012.10.007|bibcode=2012PSEP...90..475W }}{{Cite journal |last1=Boyd |first1=P. W. |last2=Watson |first2=A. J. |last3=Law |first3=C. S. |last4=Abraham |first4=E. R. |last5=Trull |first5=T. |last6=Murdoch |first6=R. |last7=Bakker |first7=D. C. |last8=Bowie |first8=A. R. |last9=Buesseler |first9=K. O. |last10=Chang |first10=H. |last11=Charette |first11=M. |last12=Croot |first12=P. |last13=Downing |first13=K. |last14=Frew |first14=R. |last15=Gall |first15=M. |date=2000-10-12 |title=A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization |url=https://pubmed.ncbi.nlm.nih.gov/11048709/ |journal=Nature |volume=407 |issue=6805 |pages=695–702 |doi=10.1038/35037500 |issn=0028-0836 |pmid=11048709|bibcode=2000Natur.407..695B }}

In addition to ecological concerns, there are challenges related to the effectiveness and long-term stability of carbon sequestration through iron fertilisation. While phytoplankton can capture {{CO2}} and sink to the ocean floor, a significant portion of this carbon may eventually be released back into the atmosphere due to various oceanic processes, diminishing the technique's long-term effectiveness. {{Cite journal |last1=De Pryck |first1=Kari |last2=Boettcher |first2=Miranda |date=2024-03-01 |title=The rise, fall and rebirth of ocean carbon sequestration as a climate 'solution' |url=https://www.sciencedirect.com/science/article/pii/S0959378024000244 |journal=Global Environmental Change |volume=85 |pages=102820 |doi=10.1016/j.gloenvcha.2024.102820 |bibcode=2024GEC....8502820D |issn=0959-3780}} Recent research indicates that the success of carbon sequestration is highly variable, influenced by factors such as ocean currents and temperature. {{Cite journal |last1=Nayak |first1=N. |last2=Mehrotra |first2=R. |last3=Mehrotra |first3=S. |date=2022-09-01 |title=Carbon biosequestration strategies: a review |url=https://www.sciencedirect.com/science/article/pii/S2772656822000367 |journal=Carbon Capture Science & Technology |volume=4 |pages=100065 |doi=10.1016/j.ccst.2022.100065 |bibcode=2022CCST....400065N |issn=2772-6568}} Furthermore, feedback mechanisms, such as alterations in the ocean's biogeochemical cycles or changes in marine species populations, may weaken the overall effectiveness of iron fertilisation as a climate change mitigation strategy.

There are two ways of performing artificial iron fertilization: ship based direct into the ocean and atmospheric deployment.{{cite journal|author1=Franz Dietrich Oeste |author2=Renaud de Richter |author3=Tingzhen Ming |author4=Sylvain Caillol |title=Climate engineering by mimicking natural dust climate control: the iron salt aerosol method|journal= Earth System Dynamics |date=13 January 2017|volume=8|pages=1–54|doi=10.5194/esd-8-1-2017 |issue=1 |bibcode=2017ESD.....8....1O |doi-access=free }}

Trials of ocean fertilization using iron sulphate added directly to the surface water from ships are described in detail in the experiment section below.

Iron-rich dust rising into the atmosphere is a primary source of ocean iron fertilization.{{cite journal|author1=Gary Shaffer |author2=Fabrice Lambert |title=In and out of glacial extremes by way of dust−climate feedbacks|journal= Proceedings of the National Academy of Sciences of the United States of America |date=27 February 2018|volume=115|pages=2026–2031|doi=10.1073/pnas.1708174115 |issue=9 |pmc=5834668 |pmid=29440407|bibcode=2018PNAS..115.2026S |doi-access=free }} For example, wind blown dust from the Sahara desert fertilizes the Atlantic Ocean{{cite news|title=Desert Dust Feeds Deep Ocean Life|url=https://www.scientificamerican.com/article/desert-dust-feeds-deep-ocean-life/|access-date=March 30, 2019|magazine=Scientific American|date=July 16, 2014|author=Tim Radford|archive-date=March 31, 2019|archive-url=https://web.archive.org/web/20190331014718/https://www.scientificamerican.com/article/desert-dust-feeds-deep-ocean-life/|url-status=live}} and the Amazon rainforest.{{cite news|title=African dust keeps Amazon blooming|url=https://www.nature.com/news/2010/100809/full/news.2010.396.html|access-date=March 30, 2019|journal=Nature|date=August 9, 2010|author=Richard Lovett|archive-date=March 3, 2019|archive-url=https://web.archive.org/web/20190303235524/http://www.nature.com/news/2010/100809/full/news.2010.396.html|url-status=live}} The naturally occurring iron oxide in atmospheric dust reacts with hydrogen chloride from sea spray to produce iron chloride, which degrades methane and other greenhouse gases, brightens clouds and eventually falls with the rain in low concentration across a wide area of the globe. Unlike ship based deployment, no trials have been performed of increasing the natural level of atmospheric iron. Expanding this atmospheric source of iron could complement ship-based deployment.

One proposal is to boost the atmospheric iron level with iron salt aerosol. Iron(III) chloride added to the troposphere could increase natural cooling effects including methane removal, cloud brightening and ocean fertilization, helping to prevent or reverse global warming.

Martin hypothesized that increasing phytoplankton photosynthesis could slow or even reverse global warming by sequestering {{chem|CO|2}} in the sea. He died shortly thereafter during preparations for Ironex I,{{cite web|url=http://chemoce.mlml.calstate.edu/past.htm#ironex1|archive-url=https://web.archive.org/web/20040408032546/http://chemoce.mlml.calstate.edu/past.htm#ironex1|url-status=dead|archive-date=2004-04-08|title=Ironex (Iron Experiment) I}} 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.{{cite web |last=Weier |first=John |date=2001-07-10 |title=John Martin (1935-1993) |url=http://earthobservatory.nasa.gov/Features/Martin/ |url-status=live |archive-url=https://web.archive.org/web/20121004043048/http://earthobservatory.nasa.gov/Features/Martin/ |archive-date=2012-10-04 |access-date=2012-08-27 |work=On the Shoulders of Giants |publisher=NASA Earth Observatory}} Thereafter 12 international ocean studies examined the phenomenon:

• Ironex II, 1995[http://www.usc.edu/uscnews/stories/2203.html Ironex II] {{webarchive|url=https://web.archive.org/web/20051225235321/http://www.usc.edu/uscnews/stories/2203.html |date=2005-12-25 }}, 1995
• SOIREE (Southern Ocean Iron Release Experiment), 1999[http://tracer.env.uea.ac.uk/soiree/ SOIREE (Southern Ocean Iron Release Experiment)] {{webarchive|url=https://web.archive.org/web/20081024231944/http://tracer.env.uea.ac.uk/soiree/ |date=2008-10-24 }}, 1999
• EisenEx (Iron Experiment), 2000[http://www.awi-bremerhaven.de/Publications/Sme2003d_abstract.html EisenEx (Iron Experiment)] {{webarchive|url=https://web.archive.org/web/20070927191605/http://www.awi-bremerhaven.de/Publications/Sme2003d_abstract.html |date=2007-09-27 }}, 2000
• SEEDS (Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study), 2001[http://www.maff.go.jp/mud/476.html SEEDS (Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study)] {{webarchive|url=https://web.archive.org/web/20060214222351/http://www.maff.go.jp/mud/476.html |date=2006-02-14 }}, 2001
• SOFeX (Southern Ocean Iron Experiments - North & South), 2002[http://www.mbari.org/expeditions/SOFeX2002/history&purpose.htm SOFeX (Southern Ocean Iron Experiments - North & South)] {{Webarchive|url=https://web.archive.org/web/20180827032906/http://www3.mbari.org/expeditions/SOFeX2002/history%26purpose.htm |date=2018-08-27 }}, 2002{{cite press release| title=Effects of Ocean Fertilization with Iron To Remove Carbon Dioxide from the Atmosphere Reported| url=http://www.whoi.edu/mr/pr.do?id=886| access-date=2007-03-31| archive-date=2006-12-31| archive-url=https://web.archive.org/web/20061231181525/http://www.whoi.edu/mr/pr.do?id=886| url-status=live}}
• SERIES (Subarctic Ecosystem Response to Iron Enrichment Study), 2002[http://www.pices.int/publications/pices_press/volume11_issue1/Jan03/SERIES.pdf SERIES (Subarctic Ecosystem Response to Iron Enrichment Study)] {{Webarchive|url=https://web.archive.org/web/20070929090045/http://www.pices.int/publications/pices_press/volume11_issue1/Jan03/SERIES.pdf |date=2007-09-29 }}, 2002
• SEEDS-II, 2004[http://www.pices.int/meetings/workshops/2005_workshops/SEEDS%20II/SEEDS_f.pdf SEEDS-II] {{Webarchive|url=https://web.archive.org/web/20060516012304/http://www.pices.int/meetings/workshops/2005_workshops/SEEDS%20II/SEEDS_f.pdf |date=2006-05-16 }}, 2004
• EIFEX (European Iron Fertilization Experiment),[http://www.olympus.net/IAPSO/abstracts05/orals/456.html EIFEX (European Iron Fertilization Experiment)] {{webarchive|url=https://web.archive.org/web/20060925040114/http://www.olympus.net/IAPSO/abstracts05/orals/456.html |date=2006-09-25 }}, 2004 A successful experiment conducted in 2004 in a mesoscale ocean eddy in the South Atlantic resulted in a bloom of diatoms, a large portion of which died and sank to the ocean floor when fertilization ended. In contrast to the LOHAFEX experiment, also conducted in a mesoscale eddy, the ocean in the selected area contained enough dissolved silicon for the diatoms to flourish.{{cite journal |last=Smetacek |first=Victor |author2=Christine Klaas |author3=Volker H. Strass |author4=Philipp Assmy |author5=Marina Montresor |author6=Boris Cisewski |author7=Nicolas Savoye |author8=Adrian Webb |author9=Francesco d’Ovidio |author10=Jesús M. Arrieta |author11=Ulrich Bathmann |author12=Richard Bellerby |author13=Gry Mine Berg |author14=Peter Croot |author15=Santiago Gonzalez |author16=Joachim Henjes |author17=Gerhard J. Herndl |author18=Linn J. Hoffmann |author19=Harry Leach |author20=Martin Losch |author21=Matthew M. Mills |author22=Craig Neill |author23=Ilka Peeken |author24=Rüdiger Röttgers |author25=Oliver Sachs |display-authors=etal |title=Deep carbon export from a Southern Ocean iron-fertilized diatom bloom |journal=Nature |date=18 July 2012 |volume=487 |pages=313–319 |doi=10.1038/nature11229 |pmid=22810695 |bibcode=2012Natur.487..313S |issue=7407 |s2cid=4304972 }}{{cite news|title=Controversial Spewed Iron Experiment Succeeds as Carbon Sink|url=http://www.scientificamerican.com/article.cfm?id=fertilizing-ocean-with-iron-sequesters-co2|access-date=July 19, 2012|newspaper=Scientific American|date=July 18, 2012|author=David Biello|archive-date=August 8, 2012|archive-url=https://web.archive.org/web/20120808090256/http://www.scientificamerican.com/article.cfm?id=fertilizing-ocean-with-iron-sequesters-co2|url-status=live}}[http://www.sciencenews.org/view/generic/id/342377/title/Field_test_stashes_climate-warming_carbon_in_deep_ocean Field test stashes climate-warming carbon in deep ocean; Strategically dumping metal puts greenhouse gas away, possibly for good] {{Webarchive|url=https://web.archive.org/web/20120726000007/http://www.sciencenews.org/view/generic/id/342377/title/Field_test_stashes_climate-warming_carbon_in_deep_ocean |date=2012-07-26 }} July 18th, 2012 Science News
• CROZEX (CROZet natural iron bloom and Export experiment), 2005[http://www.noc.soton.ac.uk/obe/PROJECTS/crozet/index.php CROZEX (CROZet natural iron bloom and Export experiment)] {{webarchive|url=https://web.archive.org/web/20110613223259/http://www.noc.soton.ac.uk/obe/PROJECTS/crozet/index.php |date=2011-06-13 }}, 2005
• A pilot project planned by Planktos, a U.S. company, was cancelled in 2008 for lack of funding.[http://www.ecoearth.info/shared/reader/welcome.aspx?linkid=75650&keybold=dust Scientists to fight global warming with plankton] {{Webarchive|url=https://web.archive.org/web/20070927103701/http://www.ecoearth.info/shared/reader/welcome.aspx?linkid=75650&keybold=dust |date=2007-09-27 }} ecoearth.info 2007-05-21 The company blamed environmental organizations for the failure.[http://news.mongabay.com/2008/0219-planktos.html Planktos kills iron fertilization project due to environmental opposition] {{webarchive|url=http://arquivo.pt/wayback/20090713072743/http://news.mongabay.com/2008/0219-planktos.html |date=2009-07-13 }} mongabay.com 2008-02-19[https://www.nytimes.com/2008/02/14/technology/14planktos.html Venture to Use Sea to Fight Warming Runs Out of Cash] {{Webarchive|url=https://web.archive.org/web/20170119111521/http://www.nytimes.com/2008/02/14/technology/14planktos.html |date=2017-01-19 }} New York Times 2008-02-14
• LOHAFEX (Indian and German Iron Fertilization Experiment), 2009{{cite web |url=http://www.eurekalert.org/pub_releases/2009-01/haog-lai011309.php |title=LOHAFEX: An Indo-German iron fertilization experiment |publisher=Eurekalert.org |access-date=2012-04-17 |archive-date=2012-04-10 |archive-url=https://web.archive.org/web/20120410185321/http://www.eurekalert.org/pub_releases/2009-01/haog-lai011309.php |url-status=live }}{{cite news | url=http://timesofindia.indiatimes.com/Earth/Tossing_iron_powder_into_ocean/articleshow/3943779.cms | work=The Times Of India | first1=Amit | last1=Bhattacharya | title=Tossing iron powder into ocean to fight global warming | date=2009-01-06 | access-date=2009-01-13 | archive-date=2009-01-11 | archive-url=https://web.archive.org/web/20090111152052/http://timesofindia.indiatimes.com/Earth/Tossing_iron_powder_into_ocean/articleshow/3943779.cms | url-status=live }}{{cite web |url=https://www.newscientist.com/article/dn16390-climate-fix-ship-sets-sail-with-plan-to-dump-iron-.html |title='Climate fix' ship sets sail with plan to dump iron - environment - 09 January 2009 |publisher=New Scientist |access-date=2012-04-17 |archive-date=2012-10-19 |archive-url=https://web.archive.org/web/20121019055014/http://www.newscientist.com/article/dn16390-climate-fix-ship-sets-sail-with-plan-to-dump-iron-.html |url-status=live }} Despite widespread opposition to LOHAFEX, on 26 January 2009 the German Federal Ministry of Education and Research (BMBF) gave clearance. The experiment was carried out in waters low in silicic acid, an essential nutrient for diatom growth. This affected sequestration efficacy.{{cite web |url=http://www.eurekalert.org/pub_releases/2009-03/haog-lpn032409.php |title=Lohafex provides new insights on plankton ecology |publisher=Eurekalert.org |access-date=2012-04-17 |archive-date=2012-09-19 |archive-url=https://web.archive.org/web/20120919143041/http://www.eurekalert.org/pub_releases/2009-03/haog-lpn032409.php |url-status=live }} A {{convert|900|km2|sqmi|sp=us}} portion of the southwest Atlantic was fertilized with iron sulfate. A large phytoplankton bloom was triggered. In the absence of diatoms, a relatively small amount of carbon was sequestered, because other phytoplankton are vulnerable to predation by zooplankton and do not sink rapidly upon death. These poor sequestration results led to suggestions that fertilization is not an effective carbon mitigation strategy in general. However, prior ocean fertilization experiments in high silica locations revealed much higher carbon sequestration rates because of diatom growth. LOHAFEX confirmed sequestration potential depends strongly upon appropriate siting.
• Haida Salmon Restoration Corporation (HSRC), 2012 - funded by the Old Massett Haida band and managed by Russ George - dumped 100 tonnes of iron sulphate into the Pacific into an eddy {{convert|200|nmi|km}} west of the islands of Haida Gwaii. This resulted in increased algae growth over {{convert|10000|sqmi}}. Critics alleged George's actions violated the United Nations Convention on Biological Diversity (CBD) and the London convention on the dumping of wastes at sea which prohibited such geoengineering experiments.{{cite news|title=World's biggest geoengineering experiment 'violates' UN rules: Controversial US businessman's iron fertilisation off west coast of Canada contravenes two UN conventions|url=https://www.theguardian.com/environment/2012/oct/15/pacific-iron-fertilisation-geoengineering|access-date=October 16, 2012|newspaper=The Guardian|date=October 15, 2012|author=Martin Lukacs|archive-date=October 12, 2013|archive-url=https://web.archive.org/web/20131012062020/http://www.theguardian.com/environment/2012/oct/15/pacific-iron-fertilisation-geoengineering|url-status=live}}{{cite news|title=A Rogue Climate Experiment Outrages Scientists|url=https://www.nytimes.com/2012/10/19/science/earth/iron-dumping-experiment-in-pacific-alarms-marine-experts.html|access-date=October 19, 2012|newspaper=The New York Times|date=October 18, 2012|author=Henry Fountain|archive-date=October 18, 2012|archive-url=https://web.archive.org/web/20121018203348/http://www.nytimes.com//2012/10/19/science/earth/iron-dumping-experiment-in-pacific-alarms-marine-experts.html|url-status=live}} On 15 July 2014, the resulting scientific data was made available to the public.{{cite web|url=http://www.whoi.edu/ocb-fert/page.do?pid=38315|title=Home: OCB Ocean Fertilization|publisher=Woods Hole Oceanographic Institution|archive-url=https://web.archive.org/web/20150312221134/https://www.whoi.edu/ocb-fert/page.do?pid=38315|archive-date=2015-03-12}}

John Martin, director of the Moss Landing Marine Laboratories, hypothesized that the low levels of phytoplankton in these regions are due to a lack of iron. In 1989 he tested this hypothesis (known as the Iron Hypothesis) by an experiment using samples of clean water from Antarctica.{{Cite web |title=The Iron Hypothesis |url=http://www.homepages.ed.ac.uk/shs/Climatechange/Carbon%20sequestration/Martin%20iron.htm#:~:text=John%20Martin%27s%20iron%20hypothesis%E2%80%94fertilizing,in%20turn%20cool%20the%20planet. |url-status=live |archive-url=https://web.archive.org/web/20201105173111/http://www.homepages.ed.ac.uk/shs/Climatechange/Carbon%20sequestration/Martin%20iron.htm#:~:text=John%20Martin%27s%20iron%20hypothesis%E2%80%94fertilizing,in%20turn%20cool%20the%20planet. |archive-date=5 November 2020 |access-date=2020-07-26 |website=homepages.ed.ac.uk}} Iron was added to some of these samples. After several days the phytoplankton in the samples with iron fertilization 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.{{cite web |author=John Weier |date=2001-07-10 |title=The Iron Hypothesis |url=http://earthobservatory.nasa.gov/Features/Martin/martin_4.php |url-status=live |archive-url=https://web.archive.org/web/20121004134105/http://earthobservatory.nasa.gov/Features/Martin/martin_4.php |archive-date=4 October 2012 |access-date=27 August 2012 |work=John Martin (1935–1993)}}

This experiment was followed by a 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 experimental area.{{cite web |author=John Weier |date=2001-07-10 |title=Following the vision |url=http://earthobservatory.nasa.gov/Features/Martin/martin_5.php |url-status=live |archive-url=https://web.archive.org/web/20121015071142/http://earthobservatory.nasa.gov/Features/Martin/martin_5.php |archive-date=15 October 2012 |access-date=27 August 2012 |work=John Martin (1935–1993)}} The success of this experiment and others led to proposals to use this technique to remove carbon dioxide from the atmosphere.{{Cite news |last=Richtel |first=Matt |date=2007-05-01 |title=Recruiting Plankton to Fight Global Warming |work=The New York Times |url=https://www.nytimes.com/2007/05/01/business/01plankton.html |url-status=live |access-date=2017-06-03 |archive-url=https://web.archive.org/web/20170408032457/http://www.nytimes.com/2007/05/01/business/01plankton.html |archive-date=8 April 2017}}

In 2000 and 2004, iron sulfate was discharged from the EisenEx. 10 to 20 percent of the resulting algal bloom died and sank to the sea floor.{{Cite journal |last1=Bakker |first1=Dorothee C. E. |last2=Bozec |first2=Yann |last3=Nightingale |first3=Philip D. |last4=Goldson |first4=Laura |last5=Messias |first5=Marie-José |last6=de Baar |first6=Hein J. W. |last7=Liddicoat |first7=Malcolm |last8=Skjelvan |first8=Ingunn |last9=Strass |first9=Volker |last10=Watson |first10=Andrew J. |date=2005-06-01 |title=Iron and mixing affect biological carbon uptake in SOIREE and EisenEx, two Southern Ocean iron fertilisation experiments |url=https://www.sciencedirect.com/science/article/pii/S0967063705000051 |journal=Deep Sea Research Part I: Oceanographic Research Papers |language=en |volume=52 |issue=6 |pages=1001–1019 |doi=10.1016/j.dsr.2004.11.015 |bibcode=2005DSRI...52.1001B |issn=0967-0637}}

Planktos was a US company that abandoned its plans to conduct 6 iron fertilization 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. 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.{{cite web |date=2007-12-19 |title=Planktos Shareholder Update |url=http://www.pr-inside.com/planktos-shareholder-update-r356198.htm |archive-url=https://web.archive.org/web/20080625094637/http://www.pr-inside.com/planktos-shareholder-update-r356198.htm |archive-date=2008-06-25 |work=Business wire}}

In 2007 commercial companies such as Climos and GreenSea Ventures and the Australian-based Ocean Nourishment Corporation, planned to engage in fertilization projects. These companies invited green co-sponsors to finance their activities in return for provision of carbon credits to offset investors' CO₂ emissions.{{cite web |last=Salleh |first=Anna |year=2007 |title=Urea 'climate solution' may backfire |url=http://www.abc.net.au/science/news/stories/2007/2085584.htm |archive-url=https://web.archive.org/web/20081118051549/http://www.abc.net.au/science/news/stories/2007/2085584.htm |archive-date=2008-11-18 |work=ABC Science Online}}

LOHAFEX was an experiment initiated by the German Federal Ministry of Research and carried out by the German Alfred Wegener Institute (AWI) in 2009 to study fertilization in the South Atlantic. India was also involved.{{cite web |title=Alfred-Wegener-Institut für Polar- und Meeresforschung (AWI) ANT-XXV/3 |url=http://www.awi.de/de/infrastruktur/schiffe/polarstern/wochenberichte/alle_expeditionen/ant_xxv/ant_xxv3/ |url-status=dead |archive-url=https://web.archive.org/web/20121008092855/http://www.awi.de/de/infrastruktur/schiffe/polarstern/wochenberichte/alle_expeditionen/ant_xxv/ant_xxv3/ |archive-date=8 October 2012 |access-date=9 August 2012}}

As part of the experiment, the German research vessel Polarstern deposited 6 tons of ferrous sulfate in an area of 300 square kilometers. It was expected that the material would distribute through the upper {{convert|15|m}} 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 Federal Environment Ministry called for the experiment to halt, partly because environmentalists predicted damage to marine plants. Others predicted long-term effects that would not be detectable during short-term observation{{cite web |date=2009-01-14 |title=LOHAFEX über sich selbst |url=http://commonsblog.wordpress.com/2009/01/14/lohafex-uber-sich-selbst |url-status=live |archive-url=https://web.archive.org/web/20090215140136/http://commonsblog.wordpress.com/2009/01/14/lohafex-uber-sich-selbst/ |archive-date=15 February 2009 |access-date=9 August 2012}}{{Unreliable source?|date=May 2021}} or that this would encourage large-scale ecosystem manipulation.{{Cite web |last=Helfrich |first=Silke |date=2009-01-12 |title=Polarsternreise zur Manipulation der Erde |url=https://commonsblog.wordpress.com/2009/01/12/polarsternreise-zur-manipulation-der-erde/ |url-status=live |archive-url=https://web.archive.org/web/20161014115327/https://commonsblog.wordpress.com/2009/01/12/polarsternreise-zur-manipulation-der-erde/ |archive-date=14 October 2016 |access-date=2017-06-03 |website=CommonsBlog}}{{Unreliable source?|date=May 2021}}{{Cite journal |last=John |first=Paull |date=2009 |title=Geo-Engineering in the Southern Ocean |url=https://core.ac.uk/display/10928574 |url-status=live |journal=Journal of Bio-Dynamics Tasmania |language=en-gb |issue=93 |archive-url=https://web.archive.org/web/20181106232459/https://core.ac.uk/display/10928574 |archive-date=6 November 2018 |access-date=2017-06-03}}

A 2012 study deposited iron fertilizer in an eddy near Antarctica. The resulting algal bloom sent a significant amount of carbon into the deep ocean, where it was expected to remain for centuries to millennia. The eddy was chosen because it offered a largely self-contained test system.{{Cite news |title=Could Fertilizing the Oceans Reduce Global Warming? |work=Live Science |url=http://www.livescience.com/21684-geoengineering-iron-fertilization-climate.html |url-status=live |access-date=2017-06-02 |archive-url=https://web.archive.org/web/20161127100143/http://www.livescience.com/21684-geoengineering-iron-fertilization-climate.html |archive-date=27 November 2016}}

As of day 24, nutrients, including nitrogen, phosphorus and silicic acid that diatoms use to construct their shells, declined. Dissolved inorganic carbon concentrations were reduced below equilibrium with atmospheric {{Chem|CO|2}}. In surface water, particulate organic matter (algal remains) including silica and chlorophyll increased.

After day 24, however, the particulate matter fell to between {{Convert|100|m}} to the ocean floor. Each iron atom converted at least 13,000 carbon atoms into algae. At least half of the organic matter sank below, {{convert|1000|m}}.

In July 2012, the Haida Salmon Restoration Corporation dispersed {{convert|100|ST|0}} of iron sulphate dust into the Pacific Ocean several hundred miles west of the islands of Haida Gwaii. The Old Massett Village Council financed the action as a salmon enhancement project with $2.5 million in village funds.{{cite news |author=Lucas, Martin |date=15 October 2012 |title=World's biggest geoengineering experiment 'violates' UN rules |newspaper=The Guardian |url=https://www.theguardian.com/environment/2012/oct/15/pacific-iron-fertilisation-geoengineering?fb=native&CMP=FBCNETTXT9038 |url-status=live |access-date=17 October 2012 |archive-url=https://web.archive.org/web/20140204004552/http://www.theguardian.com/environment/2012/oct/15/pacific-iron-fertilisation-geoengineering?fb=native&CMP=FBCNETTXT9038 |archive-date=4 February 2014}} 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 accompanied by charges of unscientific procedures and recklessness. George contended that 100 tons was negligible compared to what naturally enters the ocean.{{cite news |author=Fountain, Henry |date=18 October 2012 |title=A Rogue Climate Experiment Outrages Scientists |work=The New York Times |url=https://www.nytimes.com/2012/10/19/science/earth/iron-dumping-experiment-in-pacific-alarms-marine-experts.html?_r=0 |url-status=live |access-date=18 October 2012 |archive-url=https://web.archive.org/web/20121018181449/http://www.nytimes.com/2012/10/19/science/earth/iron-dumping-experiment-in-pacific-alarms-marine-experts.html?_r=0 |archive-date=18 October 2012}}

Some environmentalists called the dumping a "blatant violation" of two international moratoria.{{cite web |date=16 October 2012 |title=Environment Canada launches probe into massive iron sulfate dump off Haida Gwaii coast |url=http://aptn.ca/news/2012/10/16/environment-canada-launches-probe-into-massive-iron-sulphate-dump-off-haida-gwaii-coast/ |url-status=live |archive-url=https://web.archive.org/web/20140202225828/http://aptn.ca/news/2012/10/16/environment-canada-launches-probe-into-massive-iron-sulphate-dump-off-haida-gwaii-coast/ |archive-date=2 February 2014 |access-date=17 October 2012 |publisher=APTN National News}} George said that the Old Massett Village Council and its lawyers approved the effort and at least seven Canadian agencies were aware of it.

According to George, the 2013 salmon runs increased from 50 million to 226 million fish.{{cite web |last=Zubrin |first=Robert |date=2014-04-22 |title=The Pacific's Salmon Are Back – Thank Human Ingenuity |url=http://www.nationalreview.com/article/376258/pacifics-salmon-are-back-thank-human-ingenuity-robert-zubrin |url-status=live |archive-url=https://web.archive.org/web/20140423121414/http://www.nationalreview.com/article/376258/pacifics-salmon-are-back-thank-human-ingenuity-robert-zubrin |archive-date=23 April 2014 |access-date=2014-04-23 |publisher=Nationalreview.com}} However, many experts contend that changes in fishery stocks since 2012 cannot necessarily be attributed to the 2012 iron fertilization; many factors contribute to predictive models, and most data from the experiment are considered to be of questionable scientific value.{{Cite news |title=Controversial Haida Gwaii ocean fertilizing experiment pitched to Chile |language=en |work=CBC News |url=http://www.cbc.ca/news/canada/british-columbia/haida-gwaii-ocean-fertalizing-chile-1.3550783 |url-status=live |access-date=2017-11-09 |archive-url=https://web.archive.org/web/20171102150136/http://www.cbc.ca/news/canada/british-columbia/haida-gwaii-ocean-fertalizing-chile-1.3550783 |archive-date=2 November 2017}}

On 15 July 2014, the data gathered during the project were made publicly available under the ODbL license.{{Cite web |title=Welcome to the OCB Ocean Fertilization Website |url=http://www.whoi.edu/ocb-fert/page.do?pid=38315 |url-status=live |archive-url=https://web.archive.org/web/20150312221134/https://www.whoi.edu/ocb-fert/page.do?pid=38315 |archive-date=12 March 2015 |access-date=22 October 2014}}

In 2022, a UK/India research team plans to place iron-coated rice husks in the Arabian Sea, to test whether increasing time at the surface can stimulate a bloom using less iron. The iron will be confined within a plastic bag reaching from the surface several kilometers down to the sea bottom.{{cite web |url=https://pib.gov.in/PressReleaseIframePage.aspx?PRID=1779378| title=Scarcity of iron, puffing hot iron in the Arabian Sea and geoengineering climate change }}{{cite journal |title=Dissolved iron cycling in the Arabian Sea and sub-tropical gyre region of the Indian Ocean|year=2022|doi=10.1016/j.gca.2021.10.026|last1=Chinni |first1=Venkatesh |last2=Singh |first2=Sunil Kumar |journal=Geochimica et Cosmochimica Acta |volume=317 |pages=325–348 |bibcode=2022GeCoA.317..325C |s2cid=240313905 }} The Centre for Climate Repair at the University of Cambridge, along with India's Institute of Maritime Studies assessed the impact of iron seeding in another experiment. They spread iron-coated rice husks across an area of the Arabian Sea. Iron is a limiting nutrient in many ocean waters. They hoped that the iron would fertilize algae, which would bolster the bottom of the marine food chain and sequester carbon as uneaten algae died. The experiment was demolished by a storm, leaving inconclusive results.{{Cite web |last=Voosen |first=Paul |date=16 December 2022 |title=Ocean geoengineering scheme aces its first field test |url=https://www.science.org/content/article/ocean-geoengineering-scheme-aces-its-first-field-test |access-date=2022-12-19 |website=www.science.org |language=en}}

The maximum possible result from iron fertilization, assuming the most favourable conditions and disregarding practical considerations, is 0.29 W/m² of globally averaged negative forcing,{{cite journal |author=Lenton, T. M., Vaughan, N. E. |title=The radiative forcing potential of different climate geoengineering options |journal=Atmos. Chem. Phys. Discuss. |volume=9 |pages=2559–2608 |year=2009 |doi=10.5194/acpd-9-2559-2009 |url=https://ueaeprints.uea.ac.uk/24298/1/grn_lenton_vaughan_2009.pdf |doi-access=free |access-date=2019-10-01 |archive-date=2021-11-23 |archive-url=https://web.archive.org/web/20211123180746/https://ueaeprints.uea.ac.uk/id/eprint/24298/1/grn_lenton_vaughan_2009.pdf |url-status=live }} offsetting 1/6 of current levels of anthropogenic {{chem|CO|2}} emissions. These benefits have been called into question by research suggesting that fertilization with iron may deplete other essential nutrients in the seawater causing reduced phytoplankton growth elsewhere — in other words, that iron concentrations limit growth more locally than they do on a global scale.{{cite web|url=https://phys.org/news/2016-03-seeding-iron-pacific-carbon-air.html|title=Seeding iron in the Pacific may not pull carbon from air as thought|date=March 3, 2016|publisher=Phys.org|access-date=August 4, 2017|archive-date=August 4, 2017|archive-url=https://web.archive.org/web/20170804173305/https://phys.org/news/2016-03-seeding-iron-pacific-carbon-air.html|url-status=live}}{{cite journal|title=No iron fertilization in the equatorial Pacific Ocean during the last ice age|author=K. M. Costa, J. F. McManus, R. F. Anderson, H. Ren, D. M. Sigman, G. Winckler, M. Q. Fleisher, F. Marcantonio, A. C. Ravelo|journal=Nature|volume=529|issue=7587|pages=519–522|doi=10.1038/nature16453|pmid=26819045|year=2016|bibcode=2016Natur.529..519C|s2cid=205247036}}

Ocean fertilization occurs naturally when upwellings bring nutrient-rich water to the surface, as occurs when ocean currents meet an ocean bank or a sea mount. This form of fertilization produces the world's largest marine habitats. Fertilization can also occur when weather carries wind blown dust long distances over the ocean, or iron-rich minerals are carried into the ocean by glaciers,{{cite web |last=Smetacek |first=Victor |author-link=Victor Smetacek |title=Ocean fertilization |url=http://www.tyndall.ac.uk/events/past_events/ocean_fert.pdf |archive-url=https://web.archive.org/web/20071129123537/http://www.tyndall.ac.uk/events/past_events/ocean_fert.pdf |archive-date=29 November 2007}} rivers and icebergs.{{cite news |last1=Traufetter |first1=Gerald |date=2008-12-18 |title=Cold Carbon Sink: Slowing Global Warming with Antarctic Iron - Spiegel Online |newspaper=Spiegel Online |publisher=Spiegel.de |url=http://www.spiegel.de/international/world/0,1518,599213,00.html#ref=rss |url-status=live |access-date=2012-04-17 |archive-url=https://web.archive.org/web/20170413111329/http://www.spiegel.de/international/world/cold-carbon-sink-slowing-global-warming-with-antarctic-iron-a-599213.html#ref=rss |archive-date=2017-04-13}}

About 70% of the world's surface is covered in oceans. The part of these where light can penetrate is inhabited by algae (and other marine life). In some oceans, algae growth and reproduction is limited by the amount of iron. Iron is a vital micronutrient for phytoplankton growth and photosynthesis that has historically been delivered to the pelagic sea by dust storms from arid lands. This Aeolian dust contains 3–5% iron and its deposition has fallen nearly 25% in recent decades.[http://earthobservatory.nasa.gov/Newsroom/NasaNews/2003/2003091615946.html Ocean Plant Life Slows Down and Absorbs less Carbon] {{webarchive|url=https://web.archive.org/web/20070802201630/http://earthobservatory.nasa.gov/Newsroom/NasaNews/2003/2003091615946.html |date=2007-08-02 }} NASA Earth Observatory

The Redfield ratio describes the relative atomic concentrations of critical nutrients in plankton biomass and is conventionally written "106 C: 16 N: 1 P." This expresses the fact that one atom of phosphorus and 16 of nitrogen are required to "fix" 106 carbon atoms (or 106 molecules of {{chem|CO|2}}). Research expanded this constant to "106 C: 16 N: 1 P: .001 Fe" signifying that in iron deficient conditions each atom of iron can fix 106,000 atoms of carbon,{{cite journal |author1=Sunda, W. G. |author2=S. A. Huntsman |title=Iron uptake and growth limitation in oceanic and coastal phytoplankton |journal=Mar. Chem. |volume=50 |issue=1–4 |pages=189–206 |year=1995 |doi=10.1016/0304-4203(95)00035-P |bibcode=1995MarCh..50..189S |url=https://zenodo.org/record/1258477 |access-date=2020-02-06 |archive-date=2020-02-06 |archive-url=https://web.archive.org/web/20200206165120/https://zenodo.org/record/1258477 |url-status=live }} or on a mass basis, each kilogram of iron can fix 83,000 kg of carbon dioxide. The 2004 EIFEX experiment reported a carbon dioxide to iron export ratio of nearly 3000 to 1. The atomic ratio would be approximately: "3000 C: 58,000 N: 3,600 P: 1 Fe".{{cite journal |author=de Baar H . J. W., Gerringa, L. J. A., Laan, P., Timmermans, K. R |title= Efficiency of carbon removal per added iron in ocean iron fertilization|journal=Mar Ecol Prog Ser |volume=364 |pages=269–282 |year=2008 |doi=10.3354/meps07548|bibcode=2008MEPS..364..269D|doi-access=free}}

Therefore, small amounts of iron (measured by mass parts per trillion) in HNLC zones can trigger large phytoplankton blooms on the order of 100,000 kilograms of plankton per kilogram of iron. The size of the iron particles is critical. Particles of 0.5–1 micrometer or less seem to be ideal both in terms of sink rate and bioavailability. Particles this small are easier for cyanobacteria and other phytoplankton to incorporate and the churning of surface waters keeps them in the euphotic or sunlit biologically active depths without sinking for long periods. One way to add small amounts of iron to HNLC zones would be Atmospheric Methane Removal.

Atmospheric deposition is an important iron source. Satellite images and data (such as PODLER, MODIS, MSIR){{cite journal |author1=Barnaba, F. |author2=G. P. Gobbi |title=Aerosol seasonal variability over the Mediterranean region and relative impact of maritime, continental and Saharan dust particles over the basin from MODIS data in the year 2001 |journal=Atmos. Chem. Phys. Discuss. |volume=4 |issue=4 |pages=4285–4337 |year=2004 |doi=10.5194/acpd-4-4285-2004 |url=https://hal.archives-ouvertes.fr/hal-00295558/document |doi-access=free |access-date=2019-09-23 |archive-date=2019-09-23 |archive-url=https://web.archive.org/web/20190923123328/https://hal.archives-ouvertes.fr/hal-00295558/document |url-status=live }}{{cite journal |author1=Ginoux, P. |author2=O. Torres |title= Empirical TOMS index for dust aerosol: Applications to model validation and source characterization |journal= J. Geophys. Res. |volume=108 |issue= D17|pages= 4534|year=2003 |doi=10.1029/2003jd003470 |bibcode=2003JGRD..108.4534G|citeseerx=10.1.1.143.9618 }}{{cite journal |author= Kaufman, Y., I. Koren, L. A. Remer, D. Tanre, P. Ginoux, and S. Fan |title= Dust transport and deposition observed from the Terra-MODIS spacecraft over the Atlantic Ocean |journal= J. Geophys. Res.|volume= 110|issue= D10|doi=10.1029/2003jd004436|pages=D10S12|year=2005 |bibcode=2005JGRD..11010S12K|citeseerx= 10.1.1.143.7305 }} combined with back-trajectory analyses identified natural sources of iron–containing dust. Iron-bearing dusts erode from soil and are transported by wind. Although most dust sources are situated in the Northern Hemisphere, the largest dust sources are located in northern and southern Africa, North America, central Asia and Australia.{{cite journal|author=Mahowald|first=Natalie M.|author-link=Natalie Mahowald|display-authors=etal|year=2005|title=Atmospheric global dust cycle and iron inputs to the ocean.|url=https://hal.archives-ouvertes.fr/hal-02326052/file/mahowald%20et%20al.%2C%20GBC%2C%202005.pdf|journal=Global Biogeochemical Cycles|volume=19|issue=4|pages=GB4025|bibcode=2005GBioC..19.4025M|doi=10.1029/2004GB002402|hdl=11511/68526 |doi-access=free|access-date=2020-02-06|archive-date=2020-02-06|archive-url=https://web.archive.org/web/20200206171235/https://hal.archives-ouvertes.fr/hal-02326052/file/mahowald%2520et%2520al.,%2520GBC,%25202005.pdf|url-status=live}}

Heterogeneous chemical reactions in the atmosphere modify the speciation of iron in dust and may affect the bioavailability of deposited iron. The soluble form of iron is much higher in aerosols than in soil (~0.5%).{{cite journal |author= Fung, I. Y., S. K. Meyn, I. Tegen, S. C. Doney, J. G. John, and J. K. B. Bishop |title= Iron supply and demand in the upper ocean |journal= Global Biogeochem. Cycles |volume= 14 |issue= 2|pages= 697–700|year= 2000 |doi=10.1029/2000gb900001 |bibcode=2000GBioC..14..697F|doi-access= free }}{{cite journal |author= Hand, J. L., N. Mahowald, Y. Chen, R. Siefert, C. Luo, A. Subramaniam, and I. Fung |title= Estimates of soluble iron from observations and a global mineral aerosol model: Biogeochemical implications |journal= J. Geophys. Res. |volume=109 |issue= D17|pages=D17205|year= 2004 |doi=10.1029/2004jd004574 |bibcode=2004JGRD..10917205H|doi-access=free }} Several photo-chemical interactions with dissolved organic acids increase iron solubility in aerosols.{{cite journal |author= Siefert, Ronald L.|title= Iron photochemistry of aqueous suspensions of ambient aerosol with added organic acids.|journal= Geochimica et Cosmochimica Acta |volume= 58 |issue= 15|pages=3271–3279|year= 1994 |doi=10.1016/0016-7037(94)90055-8|display-authors=etal|bibcode=1994GeCoA..58.3271S}}{{cite journal |author1=Yuegang Zuo |author2=Juerg Hoigne |title= Formation of hydrogen peroxide and depletion of oxalic acid in atmospheric water by photolysis of iron (iii)-oxalato complexes |journal= Environmental Science & Technology |volume=26 |issue= 5|pages= 1014–1022|year= 1992 |doi=10.1021/es00029a022|bibcode=1992EnST...26.1014Z}} Among these, photochemical reduction of oxalate-bound Fe(III) from iron-containing minerals is important. The organic ligand forms a surface complex with the Fe (III) metal center of an iron-containing mineral (such as hematite or goethite). On exposure to solar radiation the complex is converted to an excited energy state in which the ligand, acting as bridge and an electron donor, supplies an electron to Fe(III) producing soluble Fe(II).{{cite journal |author1=Siffert, Christophe |author2=Barbara Sulzberger |title= Light-induced dissolution of hematite in the presence of oxalate. A case study|journal= Langmuir |volume= 7|issue= 8|pages= 1627–1634|year= 1991 |doi=10.1021/la00056a014}}{{cite journal |author= Banwart, Steven, Simon Davies, and Werner Stumm |title= The role of oxalate in accelerating the reductive dissolution of hematite (α-Fe ₂ O ₃) by ascorbate. |journal= Colloids and Surfaces |volume=39 |issue= 2|pages=303–309|year= 1989 |doi=10.1016/0166-6622(89)80281-1|doi-access=free }}{{cite journal |author1=Sulzberger, Barbara |author2=Hansulrich Laubscher |title= Reactivity of various types of iron (III)(hydr) oxides towards light-induced dissolution |journal= Marine Chemistry |volume=50.1 |issue= 1–4|pages= 103–115|year=1995 |doi=10.1016/0304-4203(95)00030-u|bibcode=1995MarCh..50..103S }} Consistent with this, studies documented a distinct diel variation in the concentrations of Fe (II) and Fe(III) in which daytime Fe(II) concentrations exceed those of Fe(III).{{cite journal |author= Kieber, R., Skrabal, S., Smith, B., and Willey |title= Organic complexation of Fe (II) and its impact on the redox cycling of iron in rain |journal= Environmental Science & Technology |volume=39 |issue= 6|pages=1576–1583|year=2005 |doi=10.1021/es040439h|pmid= 15819212 |bibcode=2005EnST...39.1576K}}{{cite journal |author= Kieber, R. J., Peake, B., Willey, J. D., and Jacobs, B |title= Iron speciation and hydrogen peroxide concentrations in New Zealand rainwater |journal= Atmospheric Environment |volume=35 |issue= 34|pages=6041–6048|year=2001b |doi=10.1016/s1352-2310(01)00199-6|bibcode=2001AtmEn..35.6041K}}{{cite journal |author= Kieber, R. J., Willey, J. D., and Avery, G. B. |title= Temporal variability of rainwater iron speciation at the Bermuda Atlantic Time Series Station |journal= Journal of Geophysical Research: Oceans |volume=108 |issue= C8|pages= 1978–2012|year=2003 |doi=10.1029/2001jc001031 |bibcode=2003JGRC..108.3277K|doi-access=free }}{{cite journal |author= Willey, J. D., Kieber, R. J., Seaton, P. J., and Miller, C. |title= Rainwater as a source of Fe (II)-stabilizing ligands to seawater |journal= Limnology and Oceanography |volume=53 |issue=4 |pages= 1678–1684|year=2008| doi = 10.4319/lo.2008.53.4.1678 |bibcode=2008LimOc..53.1678W|doi-access= free }}

Volcanic ash has a significant role in supplying the world's oceans with iron.{{cite journal | author = Duggen S. | display-authors = etal | year = 2007 | title = Subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth: Evidence from biogeochemical experiments and satellite data | url = http://oceanrep.geomar.de/4138/1/Duggen2007.pdf | journal = Geophysical Research Letters | volume = 34 | issue = 1 | pages = L01612 | doi = 10.1029/2006gl027522 | bibcode = 2007GeoRL..34.1612D | s2cid = 44686878 | access-date = 2020-02-06 | archive-date = 2021-08-10 | archive-url = https://web.archive.org/web/20210810122412/https://oceanrep.geomar.de/4138/1/Duggen2007.pdf | url-status = live }} Volcanic ash is composed of glass shards, pyrogenic minerals, lithic particles and other forms of ash that release nutrients at different rates depending on structure and the type of reaction caused by contact with water.{{cite journal | author = Olgun N. | display-authors = etal | year = 2011 | title = Surface Ocean Iron Fertilization: The role of airborne volcanic ash from subduction zone and hot spot volcanoes and related iron fluxes into the Pacific Ocean | doi = 10.1029/2009gb003761 | journal = Global Biogeochemical Cycles | volume = 25 | issue = 4 | pages = n/a | bibcode = 2011GBioC..25.4001O | url = http://oceanrep.geomar.de/10133/1/2009GB003761.pdf | doi-access = free | access-date = 2020-02-06 | archive-date = 2021-08-10 | archive-url = https://web.archive.org/web/20210810122119/https://oceanrep.geomar.de/10133/1/2009GB003761.pdf | url-status = live }}

Increases of biogenic opal in the sediment record are associated with increased iron accumulation over the last million years.{{cite journal | author = Murray Richard W., Leinen Margaret, Knowlton Christopher W. | year = 2012 | title = Links between iron input and opal deposition in the Pleistocene equatorial Pacific Ocean | journal = Nature Geoscience | volume = 5 | issue = 4| pages = 270–274 | doi=10.1038/ngeo1422| bibcode = 2012NatGe...5..270M }} In August 2008, an eruption in the Aleutian Islands deposited ash in the nutrient-limited Northeast Pacific. This ash and iron deposition resulted in one of the largest phytoplankton blooms observed in the subarctic.{{cite journal | author = Hemme R.|display-authors=etal | year = 2010 | title = Volcanic ash fuels anomalous plankton bloom in subarctic northeast Pacific | doi = 10.1029/2010gl044629 | journal = Geophysical Research Letters | volume = 37 | issue = 19|pages=n/a | bibcode=2010GeoRL..3719604H| doi-access = free }}

{{Main|Carbon sequestration}}

Previous instances of biological carbon sequestration triggered major climatic changes, lowering the temperature of the planet, such as the Azolla event. Plankton that generate calcium or silicon carbonate skeletons, such as diatoms, coccolithophores and foraminifera, account for most direct sequestration.{{Citation needed|reason=Limestone deposition by calcites add CO2 to the admostphere |date=February 2019}} 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 steadily falls thousands of meters below active plankton blooms.{{cite web|url=http://www.coml.org/medres/img/mir2dive1clip108.mpg|title=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|url-status=dead|archive-url=https://web.archive.org/web/20060908015726/http://www.coml.org/medres/img/mir2dive1clip108.mpg|archive-date=2006-09-08}}

Of the carbon-rich biomass generated by plankton blooms, half (or more) is generally consumed by grazing organisms (zooplankton, krill, small fish, etc.) but 20 to 30% sinks below {{convert|200|m|ft|sp=us}} into the colder water strata below the thermocline.{{Cite web|url=https://www.nature.com/scitable/knowledge/library/the-biological-productivity-of-the-ocean-70631104/|title=The Biological Productivity of the Ocean | Learn Science at Scitable|access-date=2021-04-22|archive-date=2021-05-03|archive-url=https://web.archive.org/web/20210503090626/https://www.nature.com/scitable/knowledge/library/the-biological-productivity-of-the-ocean-70631104/|url-status=live}} Much of this fixed carbon continues into the abyss, 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.

Evaluation of the biological effects and verification of the amount of carbon actually sequestered by any particular bloom involves a variety of measurements, combining ship-borne and remote sampling, submarine filtration traps, tracking buoy spectroscopy and satellite telemetry. Unpredictable ocean currents can remove experimental iron patches from the pelagic zone, invalidating the experiment.

The potential of fertilization to tackle global warming is illustrated by the following figures. If phytoplankton converted all the nitrate and phosphate present in the surface mixed layer across the entire Antarctic circumpolar current into organic carbon, the resulting carbon dioxide deficit could be compensated by uptake from the atmosphere amounting to about 0.8 to 1.4 gigatonnes of carbon per year.{{cite journal |author=Schiermeier Q |title=Climate change: The oresmen |journal=Nature |volume=421 |issue=6919 |pages=109–10 |date=January 2003 |pmid=12520274 |doi=10.1038/421109a |bibcode=2003Natur.421..109S |s2cid=4384209 |doi-access=free }} This quantity is comparable in magnitude to annual anthropogenic fossil fuels combustion of approximately 6 gigatonnes. The Antarctic circumpolar current region is one of several in which iron fertilization could be conducted—the Galapagos islands area another potentially suitable location.

File:CLAW hypothesis graphic 1 AYool.png

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 potentially increase cloud cover. This may increase the albedo of the planet and so cause cooling—this proposed mechanism is central to the CLAW hypothesis.{{cite journal |doi=10.1038/326655a0 |author=Charlson, R. J. |author2=Lovelock, J. E. |author3=Andreae, M. O. |author4=Warren, S. G. |title=Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate |journal=Nature |volume=326 |issue=6114 |pages=655–661 |year=1987 |bibcode=1987Natur.326..655C |s2cid=4321239 |author-link=Robert Jay Charlson |author2-link=James Lovelock }} This is one of the examples used by James Lovelock to illustrate his Gaia hypothesis.{{cite book | last = Lovelock | first = J.E. | title = Gaia: A New Look at Life on Earth | orig-year =1979 | edition = 3rd | year = 2000 | publisher = Oxford University Press | isbn = 978-0-19-286218-1 }}

During SOFeX, DMS concentrations increased by a factor of four inside the fertilized patch. Widescale iron fertilization of the Southern Ocean could lead to significant sulfur-triggered cooling in addition to that due to the {{chem|CO|2}} uptake and that due to the ocean's albedo increase, however the amount of cooling by this particular effect is very uncertain.{{cite journal| last=Wingenter| first=Oliver W. |author2=Karl B. Haase |author3=Peter Strutton |author4=Gernot Friederich |author5=Simone Meinardi |author6=Donald R. Blake | author7-link=F. Sherwood Rowland |author7=F. Sherwood Rowland|title=Changing concentrations of CO, CH4, C5H8, CH3Br, CH3I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments |journal = Proceedings of the National Academy of Sciences | volume =101 | issue = 23 | pages = 8537–8541 | date =2004-06-08 |doi=10.1073/pnas.0402744101| pmid=15173582| pmc=423229|bibcode = 2004PNAS..101.8537W | doi-access=free }}

Beginning with the Kyoto Protocol, several countries and the European Union established carbon offset markets which trade certified emission reduction credits (CERs) and other types of carbon credit instruments. In 2007 CERs sold for approximately €15–20/ton {{chem|CO|2|e}}.{{Cite web |title=February 2007 Carbon Update |url=http://www.co2australia.com.au/site/files/ul/data_text30/287647.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070830170854/http://www.co2australia.com.au/site/files/ul/data_text30/287647.pdf |archive-date=30 August 2007 |website=CO2 Australia Limited}} Iron fertilization is relatively inexpensive compared to scrubbing, direct injection and other industrial approaches, and can theoretically sequester for less than €5/ton {{chem|CO|2}}, creating a substantial return.{{cite web|url=http://scienceline.org/2007/06/08/environment-sergo-carbonsequestration/Greening-up|title=Greening Up|website=Scienceline}}{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }} In August, 2010, Russia established a minimum price of €10/ton for offsets to reduce uncertainty for offset providers.{{cite web|url=http://www.envirotech-online.com/news/environmental-analysis/7/breaking_news/russia_sets_minimum_carbon_offset_price/11355/|title=Russia sets minimum carbon offset price Envirotech Online|website=www.envirotech-online.com|access-date=2010-11-19|archive-date=2011-07-10|archive-url=https://web.archive.org/web/20110710194254/http://www.envirotech-online.com/news/environmental-analysis/7/breaking_news/russia_sets_minimum_carbon_offset_price/11355/|url-status=live}} Scientists have reported a 6–12% decline in global plankton production since 1980.[http://news.bbc.co.uk/1/hi/sci/tech/5298004.stm Plankton Found to Absorb Less Carbon Dioxide] {{Webarchive|url=https://web.archive.org/web/20060906105657/http://news.bbc.co.uk/1/hi/sci/tech/5298004.stm |date=2006-09-06 }} BBC, 8/30/06 A full-scale plankton restoration program could regenerate approximately 3–5 billion tons of sequestration capacity worth €50-100 billion in carbon offset value. However, a 2013 study indicates the cost versus benefits of iron fertilization puts it behind carbon capture and storage and carbon taxes.[http://sydney.edu.au/news/84.html?newsstoryid=10740 Iron fertilisation sunk as an ocean carbon storage solution] {{Webarchive|url=https://web.archive.org/web/20130413021908/http://sydney.edu.au/news/84.html?newsstoryid=10740 |date=2013-04-13 }} University of Sydney press release 12 December 2012 and Harrison, D P IJGW (2013)

{{More citations needed|section|date=January 2009}}

While ocean iron fertilization could represent a potent means to slow global warming, there is a current debate surrounding the efficacy of this strategy and the potential adverse effects of this.

{{main|Precautionary principle}}

The precautionary principle is a proposed guideline regarding environmental conservation. According to an article published in 2021, the precautionary principle (PP) is a concept that states, "The PP means that when it is scientifically plausible that human activities may lead to morally unacceptable harm, actions shall be taken to avoid or diminish that harm: uncertainty should not be an excuse to delay action."{{Cite journal |last1=Drivdal |first1=Laura |last2=van der Sluijs |first2=Jeroen P |date=August 2021 |title=Pollinator conservation requires a stronger and broader application of the precautionary principle |journal=Current Opinion in Insect Science |volume=46 |pages=95–105 |doi=10.1016/j.cois.2021.04.005 |pmid=33930597 |s2cid=233470544 |issn=2214-5745|doi-access=free |bibcode=2021COIS...46...95D }} Based on this principle, and because there is little data quantifying the effects of iron fertilization, it is the responsibility of leaders in this field to avoid the harmful effects of this procedure. This school of thought is one argument against using iron fertilization on a wide scale, at least until more data is available to analyze the repercussions of this.

{{main|Harmful algal bloom}}

Image:La-Jolla-Red-Tide.780.jpg.]]

Critics are concerned that fertilization will create harmful algal blooms (HAB) as many toxic algae are often favored when iron is deposited into the marine ecosystem. A 2010 study of iron fertilization in an oceanic high-nitrate, low-chlorophyll environment, however, found that fertilized Pseudo-nitzschia diatom spp., which are generally nontoxic in the open ocean, began producing toxic levels of domoic acid. Even short-lived blooms containing such toxins could have detrimental effects on marine food webs.{{cite journal |author=Tricka, Charles G., Brian D. Bill, William P. Cochlan, Mark L. Wells, Vera L. Trainer, and Lisa D. Pickell |year=2010 |title=Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas |journal=PNAS |volume=107 |issue=13 |pages=5887–5892 |bibcode=2010PNAS..107.5887T |doi=10.1073/pnas.0910579107 |pmc=2851856 |pmid=20231473 |doi-access=free}} Most species of phytoplankton are harmless or beneficial, given that they constitute the base of the marine food chain. Fertilization increases phytoplankton only in the open oceans (far from shore) where iron deficiency is substantial. Most coastal waters are replete with iron and adding more has no useful effect.{{Cite journal|last1=JK|first1=Moore|last2=SC|first2=Doney|last3=DM|first3=Glover|last4=IY|first4=Fung|date=2002-01-19|title=Iron cycling and nutrient-limitation patterns in surface waters of the world ocean|url=http://escholarship.org/uc/item/17x1c4nh|journal=Deep-Sea Research Part II: Topical Studies in Oceanography|language=en|volume=49|issue=1–3|doi=10.1016/S0967-0645(01)00109-6|issn=0967-0645|pages=463–507|bibcode=2001DSRII..49..463M|access-date=2017-09-30|archive-date=2017-10-01|archive-url=https://web.archive.org/web/20171001031316/http://escholarship.org/uc/item/17x1c4nh|url-status=live}} Further, it has been shown that there are often higher mineralization rates with iron fertilization, leading to a turn over in the plankton masses that are produced. This results in no beneficial effects and actually causes an increase in CO₂.{{Cite journal |last1=Boyd |first1=P.W. |last2=Jickells |first2=T |last3=Law |first3=CS |last4=Blain |first4=S |last5=Boyle |first5=EA |last6=Buesseler |first6=KO |last7=Coale |first7=KH |last8=Cullen |first8=JJ |last9=De Baar |first9=HJ |last10=Follows |first10=M |last11=Harvey |first11=M. |last12=Lancelot |first12=C. |last13=Levasseur |first13=M. |last14=Owens |first14=N. P. J. |last15=Pollard |first15=R. |display-authors=etal |year=2007 |title=Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions |url=http://marine.rutgers.edu/ebme/HistoryEarthSystems/HistEarthSystems_Fall2008/Week8b/Boyd_et_al_Science_2007.pdf |url-status=live |journal=Science |volume=315 |issue=5812 |pages=612–7 |bibcode=2007Sci...315..612B |doi=10.1126/science.1131669 |pmid=17272712 |archive-url=https://web.archive.org/web/20120305060552/http://marine.rutgers.edu/ebme/HistoryEarthSystems/HistEarthSystems_Fall2008/Week8b/Boyd_et_al_Science_2007.pdf |archive-date=2012-03-05 |access-date=2009-03-27 |last16=Rivkin |first16=R. B. |last17=Sarmiento |first17=J. |last18=Schoemann |first18=V. |last19=Smetacek |first19=V. |last20=Takeda |first20=S. |last21=Tsuda |first21=A. |last22=Turner |first22=S. |last23=Watson |first23=A. J. |s2cid=2476669}}

Finally, a 2010 study showed that iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas{{Cite journal| last1 =Trick| first1 =Charles G. |author2=Brian D. Bill |author3=William P. Cochlan |author4=Mark L. Wells |author5=Vera L. Trainer |author6=Lisa D. Pickell | title = Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas| journal =Proceedings of the National Academy of Sciences of the United States of America| volume = 107 | pages = 5887–5892 |year = 2010 | issue=13 | doi=10.1073/pnas.0910579107 | pmid=20231473 | pmc=2851856|bibcode=2010PNAS..107.5887T | doi-access =free }} which, the authors argue, raises "serious concerns over the net benefit and sustainability of large-scale iron fertilizations". Nitrogen released by cetaceans and iron chelate are a significant benefit to the marine food chain in addition to sequestering carbon for long periods of time.{{cite web|url=https://www.sciencedaily.com/releases/2010/10/101012101255.htm|title=Whale poop pumps up ocean health|author=Brown, Joshua E.|date=12 Oct 2010|website=Science Daily|access-date=18 August 2014|archive-date=2 September 2019|archive-url=https://web.archive.org/web/20190902084205/https://www.sciencedaily.com/releases/2010/10/101012101255.htm|url-status=live}}

A 2009 study tested the potential of iron fertilization to reduce both atmospheric CO₂ and ocean acidity using a global ocean carbon model. The study found that, "Our simulations show that ocean iron fertilization, even in the extreme scenario by depleting global surface macronutrient concentration to zero at all time, has a minor effect on mitigating CO2-induced acidification at the surface ocean."{{Cite journal|last1=Cao|first1=Long|last2=Caldeira|first2=Ken|title=Can ocean iron fertilization mitigate ocean acidification?|journal=Climatic Change|language=en|volume=99|issue=1–2|pages=303–311|doi=10.1007/s10584-010-9799-4|year=2010|bibcode=2010ClCh...99..303C|s2cid=153613458}} Unfortunately, the impact on ocean acidification would likely not change due to the low effects that iron fertilization has on CO₂ levels.

Consideration of iron's importance to phytoplankton growth and photosynthesis dates to the 1930s when Dr Thomas John Hart, a British marine biologist based on the {{RRS|Discovery II}} in the Southern Ocean speculated - in "On the phytoplankton of the South-West Atlantic and Bellingshausen Sea, 1929-31" - that great "desolate zones" (areas apparently rich in nutrients, but lacking in phytoplankton activity or other sea life) might be iron-deficient. Hart returned to this issue in a 1942 paper entitled "Phytoplankton periodicity in Antarctic surface waters", but little other scientific discussion was recorded until the 1980s, when oceanographer John Martin of the Moss Landing Marine Laboratories renewed controversy on the topic with his marine water nutrient analyses. His studies supported Hart's hypothesis. These "desolate" regions came to be called "high-nutrient, low-chlorophyll regions" (HNLC).

John Gribbin was the first scientist to publicly suggest that climate change could be reduced by adding large amounts of soluble iron to the oceans.{{Cite journal |last=Gribbin |first=John |year=1988 |title=Any old iron? |journal=Nature |volume=331 |issue=6157 |pages=570 |bibcode=1988Natur.331..570G |doi=10.1038/331570c0 |pmid=3340209 |s2cid=4281828|doi-access=free }} Martin's 1988 quip four months later at Woods Hole Oceanographic Institution, "Give me a half a tanker of iron and I will give you an ice age,"{{Cite web |title=Fertilizing the Ocean with Iron |url=https://www.whoi.edu/oceanus/feature/fertilizing-the-ocean-with-iron/ |url-status=live |archive-url=https://web.archive.org/web/20210118021505/https://www.whoi.edu/oceanus/feature/fertilizing-the-ocean-with-iron/ |archive-date=2021-01-18 |access-date=2021-02-25 |website=Woods Hole Oceanographic Institution |language=en-US}}{{cite web |title=Ocean Iron Fertilization – Why Dump Iron into the Ocean |url=http://www.whoi.edu/science/MCG/cafethorium/website/projects/iron.html |url-status=dead |archive-url=https://web.archive.org/web/20070210104008/http://www.whoi.edu/science/MCG/cafethorium/website/projects/iron.html |archive-date=2007-02-10 |access-date=2007-03-31 |work=Café Thorium |publisher=Woods Hole Oceanographic Institution}} drove a decade of research.

The findings suggested that iron deficiency was limiting ocean productivity and offered an approach to mitigating climate change as well. Perhaps the most dramatic support for Martin's hypothesis came with 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 oceans worldwide. This single fertilization event preceded an easily observed global decline in atmospheric {{chem|CO|2}} and a parallel pulsed increase in oxygen levels.{{cite journal |last=Watson |first=A.J. |date=1997-02-13 |title=Volcanic iron, CO₂, ocean productivity and climate |journal=Nature |volume=385 |issue=6617 |pages=587–588 |bibcode=1997Natur.385R.587W |doi=10.1038/385587b0 |s2cid=4316845}}

The parties to the London Dumping Convention adopted a non-binding resolution in 2008 on fertilization (labeled LC-LP.1(2008)). The 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".{{cite book |url=http://www.imo.org/blast/blastDataHelper.asp?data_id=24337&filename=LC-LP1%2830%29.pdf |title=Resolution LC-LP.1 (2008) On the Regulation of Ocean Fertilization |date=31 October 2008 |publisher=London Dumping Convention |access-date=9 August 2012 |archive-url=https://web.archive.org/web/20130828015637/http://www.imo.org/blast/blastDataHelper.asp?data_id=24337&filename=LC-LP1(30).pdf |archive-date=28 August 2013 |url-status=live}} An Assessment Framework for Scientific Research Involving Ocean Fertilization, regulating the dumping of wastes at sea (labeled LC-LP.2(2010)) was adopted by the Contracting Parties to the Convention in October 2010 (LC 32/LP 5).{{cite web |date=October 20, 2010 |title=Assessment Framework for scientific research involving ocean fertilization agreed |url=http://www.imo.org/MediaCentre/PressBriefings/Pages/Assessment-Framework-for-scientific-research-involving-ocean-fertilization-agreed.aspx |url-status=live |archive-url=https://web.archive.org/web/20121108070720/http://www.imo.org/mediacentre/pressbriefings/pages/assessment-framework-for-scientific-research-involving-ocean-fertilization-agreed.aspx |archive-date=8 November 2012 |access-date=9 August 2012 |publisher=International Maritime Organization}}

Multiple ocean labs, scientists and businesses have explored fertilization. Beginning in 1993, thirteen research teams completed ocean trials demonstrating that phytoplankton blooms can be stimulated by iron augmentation. Controversy remains over the effectiveness of atmospheric {{chem|CO|2}} sequestration and ecological effects. Ocean trials of ocean iron fertilization took place in 2009 in the South Atlantic by project LOHAFEX, and in July 2012 in the North Pacific off the coast of British Columbia, Canada, by the Haida Salmon Restoration Corporation (HSRC).{{cite journal |last=Tollefson |first=Jeff |date=2012-10-25 |title=Ocean-fertilization project off Canada sparks furore |journal=Nature |volume=490 |issue=7421 |pages=458–459 |bibcode=2012Natur.490..458T |doi=10.1038/490458a |pmid=23099379 |doi-access=free}}

• Carbon dioxide sink
• Iron chelate
• Ocean pipes
• Liebig's law of the minimum
• Iron cycle

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{{aquatic ecosystem topics|expanded=marine}}

{{DEFAULTSORT:Iron Fertilization}}

Category:Aquatic ecology

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