Editing Coccolithophore (section)

==Importance in global climate change==
{{Plankton sidebar|taxonomy}}

===Impact on the carbon cycle===
Coccolithophores have both long and short term effects on the [[carbon cycle]]. The production of coccoliths requires the uptake of [[dissolved inorganic carbon]] and calcium. [[Calcium carbonate]] and [[carbon dioxide]] are produced from calcium and [[bicarbonate]] by the following chemical reaction:<ref name=Mejia2011>{{citation |journal=PLOS Biology  |volume=9 |issue=6 |year=2011 |pages=e1001087 |title=Will Ion Channels Help Coccolithophores Adapt to Ocean Acidification? |first=R. |last=Mejia |doi=10.1371/journal.pbio.1001087|pmid=21713029 |pmc=3119655 |doi-access=free }}</ref>
: {{chem2|Ca(2+) + 2HCO3− <-> CaCO3 + CO2 + H2O}}

Because coccolithophores are photosynthetic organisms, they are able to use some of the {{CO2}} released in the calcification reaction for [[photosynthesis]].<ref name=Mackinder2010>{{citation |journal=Geomicrobiology Journal |volume=27 |issue=6–7 |year=2010 |pages=585–595 |title=Molecular Mechanisms Underlying Calcification in Coccolithophores |last1=Mackinder |doi=10.1080/01490451003703014|last2=Wheeler |first2=Glen |last3=Schroeder |first3=Declan |last4=Riebesell |first4=Ulf |last5=Brownlee |first5=Colin |bibcode=2010GmbJ...27..585M |s2cid=85403507 |display-authors=etal}}</ref>

However, the production of calcium carbonate drives surface alkalinity down, and in conditions of low alkalinity the {{CO2}} is instead released back into the atmosphere.<ref name=Bates1996>{{citation |journal=Marine Chemistry |volume=51 |issue=4 |year=1996 |pages=347–358 |title=Alkalinity changes in the Sargasso Sea; geochemical evidence of calfication? |last1=Bates |doi=10.1016/0304-4203(95)00068-2|last2=Michaels |first2=Anthony F. |last3=Knap |first3=Anthony H. |bibcode=1996MarCh..51..347B |display-authors=etal}}</ref>
As a result of this, researchers have postulated that large blooms of coccolithophores may contribute to global warming in the short term.<ref name=Marsh2003>{{citation |journal=Comparative Biochemistry and Physiology B |volume=136 |issue=4 |year=2003 |pages=743–754 |title=Regulation of CaCO3 formation in coccolithophores |first=M.E. |last=Marsh |doi=10.1016/s1096-4959(03)00180-5|pmid=14662299 }}</ref> A more widely accepted idea, however, is that over the long term coccolithophores contribute to an overall decrease in atmospheric {{CO2}} concentrations.  During calcification two carbon atoms are taken up and one of them becomes trapped as calcium carbonate.  This calcium carbonate sinks to the bottom of the ocean in the form of coccoliths and becomes part of sediment; thus, coccolithophores provide a sink for emitted carbon, mediating the effects of greenhouse gas emissions.<ref name=Marsh2003 />

===Evolutionary responses to ocean acidification===
Research also suggests that [[ocean acidification]] due to increasing concentrations of {{CO2}} in the atmosphere may affect the calcification machinery of coccolithophores.  This may not only affect immediate events such as increases in population or coccolith production, but also may induce [[evolutionary adaptation]] of coccolithophore species over longer periods of time.  For example, coccolithophores use H<sup>+</sup> [[ion channels]] in to constantly pump H<sup>+</sup> ions out of the cell during coccolith production.  This allows them to avoid [[acidosis]], as coccolith production would otherwise produce a toxic excess of H<sup>+</sup> ions.  When the function of these ion channels is disrupted, the coccolithophores stop the calcification process to avoid acidosis, thus forming a [[feedback loop]].<ref name=Beaufort2011>{{citation |journal=Nature |volume=476 |issue=7358 |year=2011 |pages=80–3 |title=Sensitivity of coccolithophores to carbonate chemistry and ocean acidification |first=L. |last=Beaufort |doi=10.1038/nature10295|pmid=21814280  |s2cid=4417285 |display-authors=etal  }}</ref> Low ocean [[alkalinity]], impairs ion channel function and therefore places evolutionary selective pressure on coccolithophores and makes them (and other ocean calcifiers) vulnerable to ocean acidification.<ref name=Tyrell1999>{{citation |journal=Journal of Geophysical Research |volume=104 |issue=C2 |year=1999 |pages=3223–3241 |title=Optical impacts of oceanic coccolithophore blooms |first1=T. |last1=Tyrell |doi=10.1029/1998jc900052 |display-authors=1 |last2=Mobley |first2=C. D. |bibcode=1999JGR...104.3223T|doi-access= }}</ref> In 2008, field evidence indicating an increase in calcification of newly formed ocean sediments containing coccolithophores bolstered the first ever experimental data showing that an increase in ocean {{CO2}} concentration results in an increase in calcification of these organisms.
Decreasing coccolith mass is related to both the increasing concentrations of {{CO2}} and decreasing concentrations of {{chem2|CO3(2−)}} in the world's oceans.  This lower calcification is assumed to put coccolithophores at ecological disadvantage.  Some species like ''Calcidiscus'' ''leptoporus'', however, are not affected in this way, while the most abundant coccolithophore species, ''E. huxleyi'' might be (study results are mixed).<ref name="Beaufort2011"/><ref name=Rodriguez2008>{{cite web |url=https://www.independent.co.uk/news/science/can-seashells-save-the-world-813915.html |title=Can seashells save the world?|website=[[Independent.co.uk]] |date=22 April 2008 }}</ref> Also, highly calcified coccolithophorids have been found in conditions of low CaCO<sub>3</sub> saturation contrary to predictions.<ref name="Smith2012"/> Understanding the effects of increasing ocean acidification on coccolithophore species is absolutely essential to predicting the future chemical composition of the ocean, particularly its carbonate chemistry.  Viable conservation and management measures will come from future research in this area.  Groups like the European-based [[CALMARO]]<ref name=Calmaro>{{cite web |url=http://www.calmaro.eu |title=cal.mar.o |access-date=2021-04-24 |archive-date=2020-12-30 |archive-url=https://web.archive.org/web/20201230012133/https://www.calmaro.eu/ |url-status=dead }}</ref> are monitoring the responses of coccolithophore populations to varying pH's and working to determine environmentally sound measures of control.

<gallery mode="packed" style="float:left" heights="200px">
File:Gephyrocapsa oceanica.jpg| ''[[Gephyrocapsa oceanica]]'' (scale bar is 1&nbsp;μm)
File:Diversity of coccolithophores (cropped) (Rhabdosphaera clavigera).jpg| ''[[Rhabdosphaera clavigera]]''
File:Diversity of coccolithophores (cropped).(Discosphaera tubifera).jpg| ''[[Discosphaera tubifera]]''
</gallery>

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===Impact on microfossil record===
{{See also|Protists in the fossil record}}

Coccolith fossils are prominent and valuable [[Microfossil#Calcareous|calcareous]] [[microfossil]]s. They are the largest global source of biogenic calcium carbonate, and significantly contribute to the global [[carbon cycle]].<ref>{{cite journal | last1 = Taylor | first1 = A.R. | last2 = Chrachri | first2 = A. | last3 = Wheeler | first3 = G. | last4 = Goddard | first4 = H. | last5 = Brownlee | first5 = C. | year = 2011 | title = A voltage-gated H<sup>+</sup> channel underlying pH homeostasis in calcifying coccolithophores | journal = PLOS Biology | volume = 9 | issue = 6| page = e1001085 | doi = 10.1371/journal.pbio.1001085 | pmid = 21713028 | pmc = 3119654 | doi-access = free }}</ref> They are the main constituent of chalk deposits such as the [[white cliffs of Dover]].

Of particular interest are fossils dating back to the [[Palaeocene-Eocene Thermal Maximum]] 55 million years ago.  This period is thought to correspond most directly to the current levels of {{CO2}} in the ocean.<ref name=Self-Trail2012>{{citation |journal=Marine Micropaleontology |volume=92–93 |year=2012 |pages=61–80 |title=Calcareous Nannofossil Assemblage Changes Across the Paleocene-Eocene Thermal Maximum: Evidence from a Shelf Setting |first1=J.M. |last1=Self-Trail |doi=10.1016/j.marmicro.2012.05.003 |display-authors=1 |last2=Watkins |first2=David K. |last3=Wandless |first3=Gregory A. |bibcode=2012MarMP..92...61S |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1466&context=geosciencefacpub }}</ref>  Finally, field evidence of coccolithophore fossils in rock were used to show that the deep-sea fossil record bears a [[megabias|rock record bias]] similar to the one that is widely accepted to affect the land-based [[fossil record]].<ref name=Lloyd2011>{{citation |journal=Geological Society, London, Special Publications |volume=358 |issue=1 |year=2011 |pages=167–177 |title=Quantifying the deep-sea rock and fossil record bias using coccolithophores |first=G.T. |last=Lloyd |doi=10.1144/sp358.11 |display-authors=etal  |bibcode = 2011GSLSP.358..167L |s2cid=129049029 }}</ref>

===Impact on the oceans===
{{See also|CLAW hypothesis}}

The coccolithophorids help in regulating the temperature of the oceans.  They thrive in warm seas and release [[dimethyl sulphide|dimethyl sulfide]] (DMS) into the air whose [[nucleation|nuclei]] help to produce thicker clouds to block the sun.<ref>{{cite journal |doi = 10.1038/326655a0|title = Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate|year = 1987|last1 = Charlson|first1 = Robert J.|last2 = Lovelock|first2 = James E.|last3 = Andreae|first3 = Meinrat O.|last4 = Warren|first4 = Stephen G.|journal = Nature|volume = 326|issue = 6114|pages = 655–661|bibcode = 1987Natur.326..655C|s2cid = 4321239}}</ref> When the oceans cool, the number of coccolithophorids decrease and the amount of clouds also decrease. When there are fewer clouds blocking the sun, the temperature also rises. This, therefore, maintains the balance and equilibrium of nature.<ref>{{cite book | author=Lovelock, James | title=The Revenge of Gaia | publisher=Penguin | year=2007 | isbn=978-0-14-102597-1| title-link=The Revenge of Gaia }}</ref><ref>{{cite journal |doi = 10.1029/2004GB002333|title = Solar variability, dimethyl sulphide, clouds, and climate|year = 2005|last1 = Larsen|first1 = S. H.|journal = Global Biogeochemical Cycles|volume = 19|issue = 1|pages = GB1014|bibcode = 2005GBioC..19.1014L| s2cid=128504924 |doi-access = }}</ref>