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{{Short description|Carbon capture process in oceans}}
{{Use British English|date=August 2021}}
{{Use dmy dates|date=August 2021}}
[[File:Oceanic Food Web.jpg|thumb|upright=1.35|{{center|The [[pelagic food web]], showing the central involvement of [[marine microorganism]]s in how the ocean imports carbon and then exports it back to the atmosphere and ocean floor}}]]

The '''biological pump''' (or '''ocean carbon biological pump''' or '''marine biological carbon pump''') is the ocean's biologically driven [[Carbon sequestration|sequestration of carbon]] from the atmosphere and land runoff to the ocean interior and [[seafloor sediments]].<ref name=Sigman2006>Sigman DM & GH Haug. 2006. The biological pump in the past. In: Treatise on Geochemistry; vol. 6, (ed.). [[Pergamon Press]], pp. 491-528</ref> In other words, it is a biologically mediated process which results in the sequestering of carbon in the deep ocean away from the atmosphere and the land. The biological pump is the biological component of the "marine carbon pump" which contains both a physical and biological component. It is the part of the broader [[oceanic carbon cycle]] responsible for the cycling of [[organic matter]] formed mainly by [[phytoplankton]] during [[photosynthesis]] (soft-tissue pump), as well as the cycling of [[calcium carbonate]] (CaCO<sub>3</sub>) formed into shells by certain organisms such as [[plankton]] and [[mollusks]] (carbonate pump).<ref name=Hain2014>{{cite book |chapter=The Biological Pump in the Past |title=Treatise on Geochemistry|edition=2|year=2014 |last1=Hain |first1=M.P. |last2=Sigman |first2=D.M. |last3=Haug |first3=G.H. |volume=8 |pages=485–517 |doi=10.1016/B978-0-08-095975-7.00618-5  |url=https://earth-system-biogeochemistry.net/wp-content/uploads/2021/05/Hain_et_al_2014_ToG.pdf |access-date=2015-06-01 |isbn=9780080983004 }}</ref>

Budget calculations of the biological carbon pump are based on the ratio between [[Marine sediment|sedimentation]] (carbon export to the ocean floor) and [[remineralization]] (release of carbon to the atmosphere).

The biological pump is not so much the result of a single process, but rather the sum of a number of processes each of which can influence biological pumping.  Overall, the pump transfers about 10.2 [[gigatonne]]s of carbon every year into the ocean's interior and a total of 1300 gigatonnes carbon over an average 127 years.<ref>{{cite journal |last1=Nowicki |first1=Michael |last2=DeVries |first2=Tim |last3=Siegel |first3=David A. |title=Quantifying the Carbon Export and Sequestration Pathways of the Ocean's Biological Carbon Pump |journal=Global Biogeochemical Cycles |date=March 2022 |volume=36 |issue=3 |doi=10.1029/2021GB007083|bibcode=2022GBioC..3607083N |s2cid=246458736 |doi-access=free }}</ref> This takes carbon out of contact with the atmosphere for several thousand years or longer. An ocean without a biological pump would result in atmospheric carbon dioxide levels about 400 [[Parts per million|ppm]] higher than the present day.

==Overview==
{{marine life sidebar}}

The element [[carbon]] plays a central role in climate and life on Earth. It is capable of moving among and between the [[geosphere]], [[cryosphere]], [[atmosphere]], [[biosphere]] and [[hydrosphere]]. This flow of carbon is referred to as the Earth's [[carbon cycle]]. It is also intimately linked to the cycling of other elements and compounds. The ocean plays a fundamental role in Earth's carbon cycle, helping to regulate atmospheric CO<sub>2</sub> concentration. The biological pump is a set of processes that transfer [[organic carbon]] from the surface to the deep ocean, and is at the heart of the [[ocean carbon cycle]].<ref name=Brewin2021 />

The biological pump depends on the fraction of primary produced [[organic matter]] that survives degradation in the [[euphotic zone]] and that is exported from surface water to the ocean interior, where it is [[Biomineralization|mineralized]] to [[inorganic carbon]], with the result that carbon is transported against the gradient of [[dissolved inorganic carbon]] (DIC) from the surface to the deep ocean. This transfer occurs through physical mixing and transport of dissolved and [[particulate organic carbon]] (POC), [[Diel vertical migration|vertical migrations]] of organisms ([[zooplankton]], [[fish]]) and through gravitational settling of particulate organic carbon.<ref name=Volk1885>{{cite book |doi = 10.1029/GM032p0099|chapter = Ocean Carbon Pumps: Analysis of Relative Strengths and Efficiencies in Ocean-Driven Atmospheric CO2 Changes|title = The Carbon Cycle and Atmospheric CO2 : Natural Variations Archean to Present|series = Geophysical Monograph Series|year = 2013|last1 = Volk|first1 = Tyler|last2 = Hoffert|first2 = Martin I.|pages = 99–110|isbn = 9781118664322}}</ref><ref name=Sarmiento2013>{{Cite book|url=https://books.google.com/books?id=QWUeAAAAQBAJ&q=%22Ocean+Biogeochemical+Dynamics%22|title = Ocean Biogeochemical Dynamics|isbn = 9781400849079|last1 = Sarmiento|first1 = Jorge L.|date = 17 July 2013|page = 526| publisher=Princeton University Press }}</ref>{{rp|526}}<ref name=Middelburg2019>{{cite book |doi = 10.1007/978-3-030-10822-9_3|chapter = The Return from Organic to Inorganic Carbon|title = Marine Carbon Biogeochemistry|series = SpringerBriefs in Earth System Sciences|year = 2019|last1 = Middelburg|first1 = Jack J.|pages = 37–56|isbn = 978-3-030-10821-2|s2cid = 104330175}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

The biological pump can be divided into three distinct phases, the first of which is the production of fixed carbon by planktonic [[phototrophs]] in the [[euphotic]] (sunlit) surface region of the ocean. In these surface waters, [[phytoplankton]] use [[carbon dioxide]] (CO<sub>2</sub>), [[nitrogen]] (N), [[phosphorus]] (P), and other trace elements ([[barium]], [[iron]], [[zinc]], etc.) during photosynthesis to make [[carbohydrates]], [[lipids]], and [[proteins]]. Some plankton, (e.g. [[coccolithophores]] and [[foraminifera]]) combine calcium (Ca) and dissolved carbonates ([[carbonic acid]] and [[bicarbonate]]) to form a calcium carbonate (CaCO<sub>3</sub>) protective coating.<ref name=DeLaRocha2014>{{cite book |doi = 10.1016/B978-0-08-095975-7.00604-5|chapter = The Biological Pump|title = Treatise on Geochemistry|year = 2014|last1 = de la Rocha|first1 = C.L.|last2 = Passow|first2 = U.|pages = 93–122|isbn = 9780080983004}}</ref>

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[[File:Components of the biological pump 2018.jpg|thumb|upright=1.203| {{center|'''Pump processes vary with depth'''}}Photic zone: 0–100 m; Mesopelagic: 100–1000 m; Bathypelagic: 1000 to abyssal depths. Below 1000 m depth carbon is considered removed from the atmosphere for at least 100 years. Scavenging: DOC incorporation within sinking particles.<ref name=Boscolo-Galazzo2018>{{cite journal |doi = 10.1016/j.gloplacha.2018.08.017|title = Temperature dependency of metabolic rates in the upper ocean: A positive feedback to global climate change?|year = 2018|last1 = Boscolo-Galazzo|first1 = F.|last2 = Crichton|first2 = K.A.|last3 = Barker|first3 = S.|last4 = Pearson|first4 = P.N.|journal = Global and Planetary Change|volume = 170|pages = 201–212|bibcode = 2018GPC...170..201B|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]] [[File:Components of the biological pump.png|thumb|upright=2.2|left| {{center|'''Components of the biological pump'''}}]]

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{{carbon cycle|pump}}

Once this carbon is fixed into soft or hard tissue, the organisms either stay in the euphotic zone to be recycled as part of the regenerative [[nutrient cycle]] or once they die, continue to the second phase of the biological pump and begin to sink to the ocean floor. The sinking particles will often form aggregates as they sink, which greatly increases the sinking rate. It is this aggregation that gives particles a better chance of escaping predation and decomposition in the water column and eventually making it to the sea floor.<ref name=DeLaRocha2014 />

The fixed carbon that is decomposed by bacteria either on the way down or once on the sea floor then enters the final phase of the pump and is remineralized to be used again in [[primary production]]. The particles that escape these processes entirely are sequestered in the sediment and may remain there for millions of years. It is this [[Carbon sequestration|sequestered carbon]] that is responsible for ultimately lowering atmospheric CO<sub>2</sub>.<ref name=DeLaRocha2014 />

Biology, physics and gravity interact to pump organic carbon into the deep sea. The processes of fixation of inorganic carbon in organic matter during photosynthesis, its transformation by food web processes (trophodynamics), physical mixing, transport and gravitational settling are referred to collectively as the biological pump.<ref name="Ducklow2001" />

The biological pump is responsible for transforming [[dissolved inorganic carbon]] (DIC) into organic biomass and pumping it in [[particulate organic carbon|particulate]] or dissolved form into the deep ocean. Inorganic nutrients and carbon dioxide are fixed during photosynthesis by phytoplankton, which both release [[dissolved organic matter]] (DOM) and are consumed by herbivorous zooplankton. Larger zooplankton - such as [[copepod]]s - [[egest]] [[fecal pellet]]s which can be reingested and sink or collect with other organic detritus into  larger, more-rapidly-sinking aggregates. DOM is partially consumed by bacteria (black dots) and respired; the remaining [[refractory DOM]] is [[advected]] and mixed into the deep sea. DOM and aggregates exported into the deep water are consumed and respired, thus returning organic carbon into the enormous deep ocean reservoir of DIC. About 1% of the particles leaving the surface ocean reach the seabed  and are consumed, respired, or buried in the sediments. There, carbon is stored for millions of years. The net effect of these processes is to remove carbon in organic form from the surface and return it to DIC at greater depths, maintaining the surface-to-deep ocean gradient of DIC. [[Thermohaline circulation]] returns deep-ocean DIC to the atmosphere on millennial timescales.<ref name=Ducklow2001 />

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==Primary production==
[[File:Size and classification of marine particles.png|thumb|upright=2|right| {{center|'''Size and classification of marine particles<ref>Monroy, P., Hernández-García, E., Rossi, V. and López, C. (2017) "Modeling the dynamical sinking of biogenic particles in oceanic flow". ''Nonlinear Processes in Geophysics'', '''24'''(2): 293–305. {{doi|10.5194/npg-24-293-2017}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License].</ref>'''<br /><small>Adapted from Simon et al., 2002.<ref>Simon, M., Grossart, H., Schweitzer, B. and [[Helle Ploug|Ploug, H.]] (2002) "Microbial ecology of organic aggregates in aquatic ecosystems". ''Aquatic microbial ecology'', '''28''': 175–211. {{doi|10.3354/ame028175}}.</ref></small>}}]]

The first step in the biological pump is the synthesis of both organic and inorganic carbon compounds by phytoplankton in the uppermost, sunlit layers of the ocean.<ref name="Sigman&Hain2012">{{cite journal |title=The Biological Productivity of the Ocean |journal=Nature Education Knowledge |year=2012 |last1=Sigman |first1=D.M. |last2=Hain |first2=M.P. |volume=3 |issue=6 |pages=1–16 |url=https://earth-system-biogeochemistry.net/wp-content/uploads/2021/05/Sigman_and_Hain_2012_NatureEdu.pdf |access-date=2015-06-01 |quote=The value of NEP [Net Ecosystem Production] depends on the boundaries defined for the ecosystem. If one considers the sunlit surface ocean down to the 1% light level (the "euphotic zone") over the course of an entire year, then NEP is equivalent to the [[particulate organic carbon]] sinking into the dark ocean interior plus the [[dissolved organic carbon]] being circulated out of the euphotic zone. In this case, NEP is also often referred to as "export production" (or "new production" (Dugdale & Goering 1967), as discussed below). }}</ref> Organic compounds in the form of sugars, carbohydrates, lipids, and proteins are synthesized during the process of [[photosynthesis]]:

CO<sub>2</sub> + H<sub>2</sub>O + light → CH<sub>2</sub>O + O<sub>2</sub>

In addition to carbon, organic matter found in phytoplankton is composed of nitrogen, phosphorus and various [[trace metals]]. The ratio of carbon to nitrogen and phosphorus varies from place to place,<ref>{{cite journal |last1=Martiny |first1=Adam C. |last2=Pham |first2=Chau T. A. |last3=Primeau |first3=Francois W. |last4=Vrugt |first4=Jasper A. |last5=Moore |first5=J. Keith |last6=Levin |first6=Simon A. |last7=Lomas |first7=Michael W. |title=Strong latitudinal patterns in the elemental ratios of marine plankton and organic matter |journal=Nature Geoscience |date=April 2013 |volume=6 |issue=4 |pages=279–283 |doi=10.1038/NGEO1757|bibcode=2013NatGe...6..279M |s2cid=5677709 |url=http://www.escholarship.org/uc/item/68n582hp }}</ref> but has an average ratio near 106C:16N:1P, known as the [[Redfield ratio]]. Trace metals such as magnesium, cadmium, iron, calcium, barium and copper are orders of magnitude less prevalent in phytoplankton organic material, but necessary for certain metabolic processes and therefore can be limiting nutrients in photosynthesis due to their lower abundance in the water column.<ref name=DeLaRocha2014 />

Oceanic primary production accounts for about half of the carbon fixation carried out on Earth. Approximately 50–60 [[Petagram|Pg]] of carbon are fixed by marine phytoplankton each year despite the fact that they account for less than 1% of the total photosynthetic biomass on Earth. The majority of this carbon fixation (~80%) is carried out in the open ocean while the remaining amount occurs in the very productive [[upwelling]] regions of the ocean. Despite these productive regions producing 2 to 3 times as much fixed carbon per area, the open ocean accounts for greater than 90% of the ocean area and therefore is the larger contributor.<ref name=DeLaRocha2014 />

==Forms of carbon==
[[File:Marine connections between the living and the nonliving.png|thumb|upright=2|right| {{center|DOM and POM }} Connections between the different compartments of the living (bacteria/viruses and phyto−/zooplankton) and the nonliving (DOM/POM and inorganic matter) environment{{hsp}}<ref name=Heinrichs2020>{{cite book |doi = 10.1007/978-3-030-20389-4_15|chapter = Complex Interactions Between Aquatic Organisms and Their Chemical Environment Elucidated from Different Perspectives|title = YOUMARES 9 - the Oceans: Our Research, Our Future|year = 2020|last1 = Heinrichs|first1 = Mara E.|last2 = Mori|first2 = Corinna|last3 = Dlugosch|first3 = Leon|pages = 279–297|isbn = 978-3-030-20388-7|s2cid = 210308256}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

===Dissolved and particulate carbon===
Phytoplankton supports all life in the ocean as it converts inorganic compounds into organic constituents. This autotrophically produced biomass presents the foundation of the marine food web.<ref name=Heinrichs2020 /> In the diagram immediately below, the arrows indicate the various production (arrowhead pointing toward DOM pool) and removal processes of DOM (arrowhead pointing away), while the dashed arrows represent dominant biological processes involved in the transfer of DOM. Due to these processes, the fraction of [[labile DOM]] decreases rapidly with depth, whereas the refractory character of the DOM pool considerably increases during its export to the deep ocean. DOM, dissolved organic matter.<ref name=Heinrichs2020 /><ref name=Carlson2002>Carlson CA (2002) [books.google.com/books?id=D6TMKZOgldAC&q=%22Production+and+removal+processes%22&pg=PA91 "Production and removal processes"]. In: Hansell DA, Carlson CA (eds) ''Biogeochemistry of marine dissolved organic matter''. Academic Press, San Diego, pages 91–151. {{ISBN|9780123238412}}.</ref>

[[File:Fate of DOM in the ocean.png|thumb|upright=2|right| {{center|'''The fate of DOM in the ocean'''}}]]

[[File:Particulate inorganic carbon budget for Hudson Bay.jpg|thumb|upright=2|right| {{center|Particulate inorganic carbon budget for Hudson Bay}} Black arrows represent DIC produced by PIC dissolution. Grey lines represent terrestrial PIC.<ref>{{cite journal |doi = 10.1016/j.pocean.2020.102319|title = Effect of terrestrial organic matter on ocean acidification and CO2 flux in an Arctic shelf sea|year = 2020|last1 = Capelle|first1 = David W.|last2 = Kuzyk|first2 = Zou Zou A.|last3 = Papakyriakou|first3 = Tim|last4 = Guéguen|first4 = Céline|last5 = Miller|first5 = Lisa A.|last6 = MacDonald|first6 = Robie W.|journal = Progress in Oceanography|volume = 185|page = 102319|bibcode = 2020PrOce.18502319C|doi-access = free|hdl = 1993/34767|hdl-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> {{space|20}} <small>Units are Tg C y<sup>−1</sup></small>]]

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===Ocean carbon pools===
The marine biological pump depends on a number of key pools, components and processes that influence its functioning. There are four main pools of carbon in the ocean.<ref name=Brewin2021>{{cite journal | last1=Brewin | first1=Robert J.W. | last2=Sathyendranath | first2=Shubha |author-link2=Shubha Sathyendranath| last3=Platt | first3=Trevor | last4=Bouman | first4=Heather | last5=Ciavatta | first5=Stefano | last6=Dall'Olmo | first6=Giorgio | last7=Dingle | first7=James | last8=Groom | first8=Steve | last9=Jönsson | first9=Bror | last10=Kostadinov | first10=Tihomir S. | last11=Kulk | first11=Gemma | last12=Laine | first12=Marko | last13=Martínez-Vicente | first13=Victor | last14=Psarra | first14=Stella | last15=Raitsos | first15=Dionysios E. | last16=Richardson | first16=Katherine | last17=Rio | first17=Marie-Hélène | last18=Rousseaux | first18=Cécile S. | last19=Salisbury | first19=Joe | last20=Shutler | first20=Jamie D. | last21=Walker | first21=Peter | title=Sensing the ocean biological carbon pump from space: A review of capabilities, concepts, research gaps and future developments | journal=Earth-Science Reviews | publisher=Elsevier BV | volume=217 | year=2021 | issn=0012-8252 | doi=10.1016/j.earscirev.2021.103604 | page=103604| bibcode=2021ESRv..21703604B | s2cid=233682755 |display-authors = 4| hdl=10871/125469 | hdl-access=free }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

* [[Dissolved inorganic carbon]] (DIC) is the largest pool. It constitutes around 38,000 [[Petagram|Pg]] C{{hsp}}<ref>{{cite journal | last=Hedges | first=John I. | title=Global biogeochemical cycles: progress and problems | journal=Marine Chemistry | publisher=Elsevier BV | volume=39 | issue=1–3 | year=1992 | issn=0304-4203 | doi=10.1016/0304-4203(92)90096-s | pages=67–93| bibcode=1992MarCh..39...67H }}</ref> and includes dissolved carbon dioxide (CO<sub>2</sub>), [[bicarbonate]] ({{chem|HCO|3|-}}), [[carbonate]] ({{chem|CO|3|2-}}), and [[carbonic acid]] ({{chem2|H2CO3|auto=on}}). The equilibrium between carbonic acid and carbonate determines the [[pH]] of the seawater. Carbon dioxide dissolves easily in water and its solubility is inversely related to temperature. Dissolved CO<sub>2</sub> is taken up in the process of photosynthesis, and can reduce the partial pressure of CO<sub>2</sub> in the seawater, favouring drawdown from the atmosphere. The reverse process respiration, releases CO<sub>2</sub> back into the water, can increase partial pressure of CO<sub>2</sub> in the seawater, favouring release back to the atmosphere. The formation of [[calcium carbonate]] by organisms such as [[coccolithophore]]s has the effect of releasing CO<sub>2</sub> into the water.<ref>{{cite book | last1=Zeebe | first1=Richard E. | last2=Wolf-Gladrow | first2=Dieter A. | title=CO2 in seawater : equilibrium, kinetics, isotopes | page=65 | publication-place=Amsterdam | date=2001 | isbn=978-0-08-052922-6 | oclc=246683387}}</ref><ref>{{cite book | last1=Rost | first1=Björn | last2=Riebesell | first2=Ulf | chapter=Coccolithophores and the biological pump: Responses to environmental changes | pages=99–125 | title=Coccolithophores | publisher=Springer Berlin Heidelberg | publication-place=Berlin, Heidelberg | year=2004 | isbn=978-3-642-06016-8 | doi=10.1007/978-3-662-06278-4_5}}</ref><ref>{{cite journal | last=Zeebe | first=Richard E. | title=History of Seawater Carbonate Chemistry, Atmospheric CO2, and Ocean Acidification | journal=Annual Review of Earth and Planetary Sciences | publisher=Annual Reviews | volume=40 | issue=1 | date=2012-05-30 | issn=0084-6597 | doi=10.1146/annurev-earth-042711-105521 | pages=141–165| bibcode=2012AREPS..40..141Z }}</ref><ref name=Brewin2021 />

* [[Dissolved organic carbon]] (DOC) is the next largest pool at around 662 Pg C.<ref name=Hansell2013a>{{cite journal | last1=Hansell | first1=Dennis A. | last2=Carlson | first2=Craig A. | title=Localized refractory dissolved organic carbon sinks in the deep ocean | journal=Global Biogeochemical Cycles | publisher=American Geophysical Union (AGU) | volume=27 | issue=3 | date=2013-08-12 | issn=0886-6236 | doi=10.1002/gbc.20067 | pages=705–710| s2cid=17175370 }}</ref> DOC can be classified according to its reactivity as refractory, semi-labile or labile. The labile pool constitutes around 0.2 Pg C, is bioavailable, and has a high production rate (~ 15−25 Pg C y<sup>−1</sup>).<ref name=Hansell2013b>{{cite journal | last=Hansell | first=Dennis A. | title=Recalcitrant Dissolved Organic Carbon Fractions | journal=Annual Review of Marine Science | publisher=Annual Reviews | volume=5 | issue=1 | date=2013-01-03 | issn=1941-1405 | doi=10.1146/annurev-marine-120710-100757 | pages=421–445| pmid=22881353 }}</ref> The refractory component is the biggest pool (~642 Pg C ± 32;<ref name=Hansell2013a /> but has a very low turnover rate (0.043 Pg C y<sup>−1</sup>).<ref name=Hansell2013b /> The turnover time for [[refractory DOC]] is thought to be greater than 1000 years.<ref>{{cite journal | last1=Williams | first1=Peter M. | last2=Druffel | first2=Ellen R. M. | title=Radiocarbon in dissolved organic matter in the central North Pacific Ocean | journal=Nature | publisher=Springer Science and Business Media LLC | volume=330 | issue=6145 | year=1987 | issn=0028-0836 | doi=10.1038/330246a0 | pages=246–248| bibcode=1987Natur.330..246W | s2cid=4329024 | url=https://escholarship.org/uc/item/8d1379dw }}</ref><ref>{{cite journal | last1=Druffel | first1=E. R. M. | last2=Griffin | first2=S. | last3=Coppola | first3=A. I. | last4=Walker | first4=B. D. | title=Radiocarbon in dissolved organic carbon of the Atlantic Ocean | journal=Geophysical Research Letters | publisher=American Geophysical Union (AGU) | volume=43 | issue=10 | date=2016-05-28 | issn=0094-8276 | doi=10.1002/2016gl068746 | pages=5279–5286| bibcode=2016GeoRL..43.5279D | s2cid=56069589 | doi-access=free }}</ref><ref name=Brewin2021 />

* [[Particulate organic carbon]] (POC) constitutes around 2.3 Pg C,<ref>{{cite journal | last1=Stramska | first1=Malgorzata | last2=Cieszyńska | first2=Agata | title=Ocean colour estimates of particulate organic carbon reservoirs in the global ocean – revisited | journal=International Journal of Remote Sensing | publisher=Informa UK Limited | volume=36 | issue=14 | date=2015-07-18 | issn=0143-1161 | doi=10.1080/01431161.2015.1049380 | pages=3675–3700| bibcode=2015IJRS...36.3675S | s2cid=128524215 }}</ref><ref>Wickland, D.E., Plummer, S. and Nakajima, M. (October 2013). "CEOS strategy for carbon observations from space". In: ''International Conference Towards a Global Carbon Observing System: Progresses and Challenges'', '''1''':. 2.</ref> and is relatively small compared with DIC and DOC. Though small in size, this pool is highly dynamic, having the highest turnover rate of any organic carbon pool on the planet.<ref>{{cite book | last=Sarmiento | first=Jorge L. | title=Ocean Biogeochemical Dynamics | publisher=Princeton University Press | date=2006-01-01 | isbn=978-1-4008-4907-9 | doi=10.1515/9781400849079}}</ref> Driven by [[Ocean primary production|primary production]], it produces around 50 Pg C y<sup>−1</sup> globally.<ref>{{cite journal | last1=Longhurst | first1=Alan | last2=Sathyendranath | first2=Shubha | last3=Platt | first3=Trevor | last4=Caverhill | first4=Carla | title=An estimate of global primary production in the ocean from satellite radiometer data | journal=Journal of Plankton Research | publisher=Oxford University Press (OUP) | volume=17 | issue=6 | year=1995 | issn=0142-7873 | doi=10.1093/plankt/17.6.1245 | pages=1245–1271}}</ref><ref>{{cite book | last1=Sathyendranath | first1=S. | last2=Platt | first2=T. | last3=Brewin | first3=Robert J.W. | last4=Jackson | first4=Thomas | title=Encyclopedia of Ocean Sciences | chapter=Primary Production Distribution | publisher=Elsevier | year=2019 | pages=635–640 | doi=10.1016/b978-0-12-409548-9.04304-9| isbn=9780128130827 }}</ref><ref>{{cite journal | last1=Kulk | first1=Gemma | last2=Platt | first2=Trevor | last3=Dingle | first3=James | last4=Jackson | first4=Thomas | last5=Jönsson | first5=Bror | last6=Bouman | first6=Heather | last7=Babin | first7=Marcel | last8=Brewin | first8=Robert | last9=Doblin | first9=Martina | last10=Estrada | first10=Marta | last11=Figueiras | first11=Francisco | last12=Furuya | first12=Ken | last13=González-Benítez | first13=Natalia | last14=Gudfinnsson | first14=Hafsteinn | last15=Gudmundsson | first15=Kristinn | last16=Huang | first16=Bangqin | last17=Isada | first17=Tomonori | last18=Kovač | first18=Žarko | last19=Lutz | first19=Vivian | last20=Marañón | first20=Emilio | last21=Raman | first21=Mini | last22=Richardson | first22=Katherine | last23=Rozema | first23=Patrick | last24=Poll | first24=Willem | last25=Segura | first25=Valeria | last26=Tilstone | first26=Gavin | last27=Uitz | first27=Julia | last28=Dongen-Vogels | first28=Virginie | last29=Yoshikawa | first29=Takashi | last30=Sathyendranath | first30=Shubha | title=Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades | journal=Remote Sensing | publisher=MDPI AG | volume=12 | issue=5 | date=2020-03-03 | issn=2072-4292 | doi=10.3390/rs12050826 | page=826| bibcode=2020RemS...12..826K |display-authors = 4| doi-access=free | hdl=11336/128979 | hdl-access=free }}</ref> It can be separated into living (e.g. [[phytoplankton]], [[zooplankton]], [[bacteria]]) and non-living (e.g. [[detritus]]) material. Of these, the phytoplankton carbon is particularly important, because of its role in [[marine primary production]], and also because it serves as the food resource for all the larger organisms in the [[Pelagic zone|pelagic ecosystem]].<ref name=Brewin2021 />

* [[Particulate inorganic carbon]] (PIC) is the smallest of the pools at around 0.03 Pg C.<ref>{{cite journal | last1=Hopkins | first1=Jason | last2=Henson | first2=Stephanie A. | last3=Poulton | first3=Alex J. | last4=Balch | first4=William M. | title=Regional Characteristics of the Temporal Variability in the Global Particulate Inorganic Carbon Inventory | journal=Global Biogeochemical Cycles | publisher=American Geophysical Union (AGU) | volume=33 | issue=11 | year=2019 | issn=0886-6236 | doi=10.1029/2019gb006300 | pages=1328–1338| bibcode=2019GBioC..33.1328H | s2cid=210342576 | doi-access=free }}</ref> It is present in the form of calcium carbonate (CaCO<sub>3</sub>) in particulate form, and impacts the carbonate system and pH of the seawater. Estimates for PIC production are in the region of 0.8–1.4 Pg C y<sup>−1</sup>, with at least 65% of it being dissolved in the upper [[water column]], the rest contributing to deep sediments.<ref name=Feely2004>{{cite journal | last1=Feely | first1=Richard A. | last2=Sabine | first2=Christopher L. | last3=Lee | first3=Kitack | last4=Berelson | first4=Will | last5=Kleypas | first5=Joanie | last6=Fabry | first6=Victoria J. | last7=Millero | first7=Frank J. | title=Impact of Anthropogenic CO 2 on the CaCO 3 System in the Oceans | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=305 | issue=5682 | date=2004-07-16 | issn=0036-8075 | doi=10.1126/science.1097329 | pages=362–366| pmid=15256664 | bibcode=2004Sci...305..362F | s2cid=31054160 }}</ref> Coccolithophores and [[foraminifera]] are estimated to be the dominant sources of PIC in the [[open ocean]].<ref>{{cite journal | last=Schiebel | first=Ralf | title=Planktic foraminiferal sedimentation and the marine calcite budget | journal=Global Biogeochemical Cycles | publisher=American Geophysical Union (AGU) | volume=16 | issue=4 | date=2002-10-24 | issn=0886-6236 | doi=10.1029/2001gb001459 | pages=3–1–3–21| bibcode=2002GBioC..16.1065S | s2cid=128737252 }}</ref><ref name=Feely2004 /> The PIC pool is of particular importance due to its role in the ocean carbonate system, and in facilitating the export of carbon to the deep ocean through the [[carbonate pump]], whereby PIC is exported out of the [[photic zone]] and deposited in the [[Marine sediment|bottom sediments]].<ref>{{cite journal | last1=Riebesell | first1=Ulf | last2=Zondervan | first2=Ingrid | last3=Rost | first3=Björn | last4=Tortell | first4=Philippe D. | last5=Zeebe | first5=Richard E. | last6=Morel | first6=François M. M. | title=Reduced calcification of marine plankton in response to increased atmospheric CO2 | journal=Nature | publisher=Springer Science and Business Media LLC | volume=407 | issue=6802 | year=2000 | issn=0028-0836 | doi=10.1038/35030078 | pages=364–367| pmid=11014189 | bibcode=2000Natur.407..364R | s2cid=4426501 | url=https://epic.awi.de/id/eprint/3784/1/Rie2000a.pdf }}</ref><ref name=Brewin2021 />

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===Calcium carbonate===
[[File:White cliffs of dover 09 2004.jpg|thumb|upright=2| {{center|The [[White Cliffs of Dover]] are made almost entirely<br />of the plates of buried coccolithophores [[#Key role of phytoplankton|( see below ↓ )]]}}]]

[[Particulate inorganic carbon]] (PIC) usually takes the form of [[calcium carbonate]] (CaCO<sub>3</sub>), and plays a key part in the ocean carbon cycle.<ref>{{cite journal |doi = 10.1002/2017JC013146|title = Estimating Particulate Inorganic Carbon Concentrations of the Global Ocean from Ocean Color Measurements Using a Reflectance Difference Approach|year = 2017|last1 = Mitchell|first1 = C.|last2 = Hu|first2 = C.|last3 = Bowler|first3 = B.|last4 = Drapeau|first4 = D.|last5 = Balch|first5 = W. M.|journal = Journal of Geophysical Research: Oceans|volume = 122|issue = 11|pages = 8707–8720|bibcode = 2017JGRC..122.8707M|doi-access = free}}</ref> This biologically fixed carbon is used as a protective coating for many planktonic species (coccolithophores, foraminifera) as well as larger marine organisms (mollusk shells). Calcium carbonate is also excreted at high rates during [[osmoregulation]] by fish, and can form in [[whiting event]]s.<ref>{{cite journal |last1=Wilson |first1=R. W. |last2=Millero |first2=F. J. |last3=Taylor |first3=J. R. |last4=Walsh |first4=P. J. |last5=Christensen |first5=V. |last6=Jennings |first6=S. |last7=Grosell |first7=M. |title=Contribution of Fish to the Marine Inorganic Carbon Cycle |journal=Science |date=16 January 2009 |volume=323 |issue=5912 |pages=359–362 |doi=10.1126/science.1157972|pmid=19150840 |bibcode=2009Sci...323..359W |s2cid=36321414 }}</ref> While this form of carbon is not directly taken from the atmospheric budget, it is formed from dissolved forms of carbonate which are in equilibrium with CO<sub>2</sub> and then responsible for removing this carbon via sequestration.<ref>Pilson MEQ. 2012. An Introduction to the Chemistry of the Sea. Cambridge University Press, pp.</ref>

CO<sub>2</sub> + H<sub>2</sub>O → H<sub>2</sub>CO<sub>3</sub> → H<sup>+</sup> + HCO<sub>3</sub><sup>−</sup>

Ca<sup>2+</sup> + 2HCO<sub>3</sub><sup>−</sup> → CaCO<sub>3</sub> + CO<sub>2</sub> + H<sub>2</sub>O

While this process does manage to fix a large amount of carbon, two units of [[alkalinity]] are sequestered for every unit of sequestered carbon.<ref name=Hain2014/><ref name="Hain et al 2010">{{cite journal|last1=Hain|first1=M.P.|last2=Sigman|first2=D.M.|last3=Haug|first3=G.H.|year=2010|title=Carbon dioxide effects of Antarctic stratification, North Atlantic Intermediate Water formation, and subantarctic nutrient drawdown during the last ice age: Diagnosis and synthesis in a geochemical box model|journal=Global Biogeochemical Cycles|volume=24|issue=4|pages=1–19|doi=10.1029/2010GB003790|bibcode=2010GBioC..24.4023H|doi-access=}}<!--|access-date=2015-06-01 --></ref>  The formation and sinking of CaCO<sub>3</sub> therefore drives a surface to deep [[alkalinity]] gradient which serves to raise the pH of surface waters, shifting the speciation of dissolved carbon to raise the [[partial pressure]] of dissolved CO<sub>2</sub> in surface waters, which actually raises atmospheric levels. In addition, the burial of CaCO<sub>3</sub> in sediments serves to lower overall oceanic [[alkalinity]], tending to raise pH and thereby atmospheric CO<sub>2</sub> levels if not counterbalanced by the new input of alkalinity from weathering.<ref name=Sigman2006 />  The portion of carbon that is permanently buried at the sea floor becomes part of the geologic record. Calcium carbonate often forms remarkable deposits that can then be raised onto land through tectonic motion as in the case with the [[White Cliffs of Dover]] in Southern England. These cliffs are made almost entirely of the plates of buried [[coccolithophore]]s.<ref name=Webb2019>Webb, Paul (2019) ''Introduction to Oceanography'', [https://rwu.pressbooks.pub/webboceanography/chapter/chapter-12-ocean-sediments/ Chapter 12: Ocean Sediments], page 273–297, Rebus Community. Updated 2020.</ref>

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==Oceanic carbon cycle==
{{main|Oceanic carbon cycle}}
[[File:OceanCarbonCycle.jpg|thumb|upright=1.5| {{center|Oceanic Carbon Cycle — IPCC}}]]

Three main processes (or pumps) that make up the marine carbon cycle bring atmospheric [[carbon dioxide]] (CO<sub>2</sub>) into the ocean interior and distribute it through the oceans.  These three pumps are: (1) the solubility pump, (2) the carbonate pump, and (3) the biological pump.  The total active pool of carbon at the Earth's surface for durations of less than 10,000 years is roughly 40,000 gigatons C (Gt C, a [[gigaton]] is one billion tons, or the weight of approximately 6 million [[blue whale]]s), and about 95% (~38,000 Gt C) is stored in the ocean, mostly as [[dissolved inorganic carbon]].<ref name=":0">{{Cite book|title=Biogeochemistry : an analysis of global change|last=H.|first=Schlesinger, William|date=2013|publisher=Academic Press|others=Bernhardt, Emily S.|isbn=9780123858740|edition=3rd|location=Waltham, Mass.|oclc=827935936}}</ref><ref>{{Cite journal|last1=Falkowski|first1=P.|last2=Scholes|first2=R. J.|last3=Boyle|first3=E.|last4=Canadell|first4=J.|last5=Canfield|first5=D.|last6=Elser|first6=J.|last7=Gruber|first7=N.|last8=Hibbard|first8=K.|last9=Högberg|first9=P.|date=2000-10-13|title=The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System|journal=Science|language=en|volume=290|issue=5490|pages=291–296|doi=10.1126/science.290.5490.291|issn=0036-8075|pmid=11030643|bibcode=2000Sci...290..291F}}</ref>  The speciation of dissolved inorganic carbon in the marine carbon cycle is a primary controller of [[Acid-base reaction|acid-base chemistry]] in the oceans.

===Solubility pump===
{{main|Solubility pump}}
[[File:CO2 pump hg.svg|thumb|upright=1.5|right| {{center|Solubility pump: Air-sea exchange of CO<sub>2</sub>}}]]

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The biological pump is accompanied by a physico-chemical counterpart known as the [[solubility pump]]. This pump transports significant amounts of carbon in the form of [[dissolved inorganic carbon]] (DIC) from the ocean's surface to its interior. It involves physical and chemical processes only, and does not involve biological processes.<ref name=raven99>{{cite journal|last=Raven|first=J. A.|author2=P. G. Falkowski|year=1999|title=Oceanic sinks for atmospheric CO<sub>2</sub>|journal=Plant, Cell and Environment|volume=22|issue=6|pages=741–755|doi=10.1046/j.1365-3040.1999.00419.x|doi-access=free}}</ref>

The solubility pump is driven by the coincidence of two processes in the ocean:
* The [[solubility]] of [[carbon dioxide]] is a strong inverse function of [[sea surface temperature|seawater temperature]] (i.e. solubility is greater in cooler water)
* The [[thermohaline circulation]] is driven by the formation of deep water at high latitudes where seawater is usually cooler and denser

Since deep water (that is, seawater in the ocean's interior) is formed under the same surface conditions that promote carbon dioxide solubility, it contains a higher concentration of dissolved inorganic carbon than might be expected from average surface concentrations.  Consequently, these two processes act together to pump carbon from the atmosphere into the ocean's interior. One consequence of this is that when deep water upwells in warmer, equatorial latitudes, it strongly outgasses carbon dioxide to the atmosphere because of the reduced solubility of the gas.<ref>{{cite journal |doi = 10.1046/j.1365-3040.1999.00419.x|title = Oceanic sinks for atmospheric CO2|year = 1999|last1 = Raven|first1 = J. A.|last2 = Falkowski|first2 = P. G.|journal = Plant, Cell and Environment|volume = 22|issue = 6|pages = 741–755|doi-access = free}}</ref>

===Carbonate pump===
The carbonate pump is sometimes referred to as the "hard tissue" component of the biological pump.<ref>{{cite journal |last1=Hain |first1=M.P. |last2=Sigman |first2=D.M. |last3=Haug |first3=G.H |title=The Biological Pump in the Past |journal=Treatise on Geochemistry |date=2014 |volume=8 |pages=485–517|doi=10.1016/B978-0-08-095975-7.00618-5 |isbn=9780080983004 }}</ref> Some surface marine organisms, like [[coccolithophore]]s, produce hard structures out of calcium carbonate, a form of particulate inorganic carbon, by fixing bicarbonate.<ref name=Rost2014>{{cite book |last1=Rost |first1=Bjorn |last2=Reibessel |first2=Ulf |title=Coccolithophores and the biological pump: responses to environmental changes |date=2004 |publisher=Springer |location=Berlin, Heidelberg |isbn=978-3-642-06016-8}}</ref> This fixation of DIC is an important part of the oceanic carbon cycle.

Ca<sup>2+</sup> + 2 HCO<sub>3</sub><sup>−</sup> → CaCO<sub>3</sub> + CO<sub>2</sub> + H<sub>2</sub>O

While the biological carbon pump fixes inorganic carbon (CO<sub>2</sub>) into [[particulate organic carbon]] in the form of sugar (C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>), the carbonate pump fixes inorganic bicarbonate and causes a net release of CO<sub>2</sub>.<ref name=Rost2014 /> In this way, the carbonate pump could be termed the carbonate counter pump. It works counter to the biological pump by counteracting the CO<sub>2</sub> flux into the biological pump.<ref>Zeebe, R.E., 2016. [https://ui.adsabs.harvard.edu/abs/2016AGUOS.B23A..08Z/abstract "The calcium carbonate counter pump: Fundamentals, evolution through time, and future feedbacks"]. ''American Geophysical Union'', pp.B23A-08.</ref>

===Continental shelf pump===
{{main|Continental shelf pump}}

The [[continental shelf pump]] is proposed as operating in the shallow waters of the [[continental shelf|continental shelves]] as a mechanism transporting carbon (dissolved or particulate) from the continental waters to the interior of the adjacent deep ocean.<ref name=tsun99>{{Cite journal | doi = 10.1034/j.1600-0889.1999.t01-2-00010.x | last1 = Tsunogai | first1 = S. | last2 = Watanabe | first2 = S. | last3 = Sato | first3 = T. | year = 1999 | title = Is there a "continental shelf pump" for the absorption of atmospheric CO<sub>2</sub> | journal = Tellus B | volume = 51 | issue = 3| pages = 701–712 |bibcode = 1999TellB..51..701T }}</ref> As originally formulated, the pump is thought to occur where the [[solubility pump]] interacts with cooler, and therefore denser water from the shelf floor which feeds down the [[continental slope]] into the neighbouring deep ocean.<ref name=tsun99/> The shallowness of the continental shelf restricts the [[convection]] of cooling water, so the cooling can be greater for continental shelf waters than for neighbouring open ocean waters. These cooler waters promote the [[solubility pump]] and lead to an increased storage of [[dissolved inorganic carbon]]. This extra carbon storage is further augmented by the increased biological production characteristic of shelves.<ref name=woll98>Wollast, R. (1998). Evaluation and comparison of the global carbon cycle in the coastal zone and in the open ocean, p. 213-252. In K. H. Brink and A. R. Robinson (eds.), ''The Global Coastal Ocean''. John Wiley & Sons.</ref> The dense, carbon-rich shelf waters then sink to the shelf floor and enter the sub-surface layer of the open ocean via [[isopycnal]] mixing.<ref name=tsun99 />  As the sea level rises in response to global warming, the surface area of the shelf seas will grow and in consequence the strength of the shelf sea pump should increase.<ref>{{Cite journal | last1=Rippeth | first1=T. P. | first2=J. D. | last2=Scourse | first3=K. | last3=Uehara | first4=S. | last4=McKeown | s2cid=1049049 | year=2008 | title=Impact of sea-level rise over the last deglacial transition on the strength of the continental shelf CO2 pump | journal=Geophys. Res. Lett. | volume=35 | issue=24 | pages=L24604 | doi=10.1029/2008GL035880 |bibcode = 2008GeoRL..3524604R | doi-access=free }}</ref>

==Processes in the biological pump==
[[File:Processes in the biological pump.webp|thumb|upright=2.2|right| {{center|'''Processes in the biological pump''' <ref name=Cavan2019 />}}{{space|8}}<small>Carbon fluxes in white boxes are in Gt C yr<sup>−1</sup> and carbon masses in dark boxes are in Gt C</small>]]

In the diagram on the right, phytoplankton convert CO<sub>2</sub>, which has dissolved from the atmosphere into the surface oceans (90 Gt yr<sup>−1</sup>), into [[particulate organic carbon]] (POC) during [[Marine primary production|primary production]] (~ 50 Gt C yr<sup>−1</sup>). Phytoplankton are then consumed by [[copepod]]s, [[krill]] and other small zooplankton grazers, which in turn are preyed upon by higher [[trophic level]]s. Any unconsumed phytoplankton form aggregates, and along with zooplankton faecal pellets, sink rapidly and are exported out of the [[mixed layer]] (< 12 Gt C yr<sup>−1</sup> 14). Krill, copepods, zooplankton and microbes intercept phytoplankton in the surface ocean and sinking detrital particles at depth, consuming and respiring this POC to CO<sub>2</sub> ([[dissolved inorganic carbon]], DIC), such that only a small proportion of surface-produced carbon sinks to the deep ocean (i.e., depths > 1000 m). As krill and smaller zooplankton feed, they also physically fragment particles into small, slower- or non-sinking pieces (via sloppy feeding, [[coprorhexy]] if fragmenting faeces),<ref>{{cite journal |doi = 10.1007/BF01313152|title = What happens to zooplankton faecal pellets? Implications for material flux|year = 1990|last1 = Lampitt|first1 = R. S.|last2 = Noji|first2 = T.|last3 = von Bodungen|first3 = B.|journal = Marine Biology|volume = 104| issue=1 |pages = 15–23| bibcode=1990MarBi.104...15L |s2cid = 86523326}}</ref> retarding POC export. This releases [[dissolved organic carbon]] (DOC) either directly from cells or indirectly via bacterial solubilisation (yellow circle around DOC). Bacteria can then [[remineralise]] the DOC to DIC (CO<sub>2</sub>, microbial gardening).<ref name=Cavan2019>Cavan, E.L., Belcher, A., Atkinson, A., Hill, S.L., Kawaguchi, S., McCormack, S., Meyer, B., Nicol, S., Ratnarajah, L., Schmidt, K. and Steinberg, D.K. (2019) "The importance of Antarctic krill in biogeochemical cycles". ''Nature communications'', '''10'''(1): 1–13. {{doi|10.1038/s41467-019-12668-7}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

The biological carbon pump is one of the chief determinants of the vertical distribution of carbon in the oceans and therefore of the surface partial pressure of CO<sub>2</sub> governing air-sea CO<sub>2</sub> exchange.<ref>{{cite journal |doi = 10.5670/oceanog.2009.48|title = Autonomous Observations of the Ocean Biological Carbon Pump|year = 2009|last1 = Bishop|first1 = James|journal = Oceanography|volume = 22|issue = 2|pages = 182–193|doi-access = free}}</ref> It comprises phytoplankton cells, their consumers and the bacteria that assimilate their waste and plays a central role in the global carbon cycle by delivering carbon from the atmosphere to the deep sea, where it is concentrated and sequestered for centuries.<ref name=Chisholm1995 /> Photosynthesis by phytoplankton lowers the partial pressure of CO<sub>2</sub> in the upper ocean, thereby facilitating the absorption of CO<sub>2</sub> from the atmosphere by generating a steeper CO<sub>2</sub> gradient.<ref>{{cite journal |doi = 10.1126/science.290.5490.291|title = The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System|year = 2000|last1 = Falkowski|first1 = P.|last2 = Scholes|first2 = R. J.|last3 = Boyle|first3 = E.|last4 = Canadell|first4 = J.|last5 = Canfield|first5 = D.|last6 = Elser|first6 = J.|last7 = Gruber|first7 = N.|last8 = Hibbard|first8 = K.|last9 = Högberg|first9 = P.|last10 = Linder|first10 = S.|last11 = MacKenzie|first11 = F. T.|last12 = Moore b|first12 = 3rd|last13 = Pedersen|first13 = T.|last14 = Rosenthal|first14 = Y.|last15 = Seitzinger|first15 = S.|last16 = Smetacek|first16 = V.|last17 = Steffen|first17 = W.|journal = Science|volume = 290|issue = 5490|pages = 291–296|pmid = 11030643|bibcode = 2000Sci...290..291F}}</ref> It also results in the formation of [[particulate organic carbon]] (POC) in the euphotic layer of the [[epipelagic zone]] (0–200 m depth). The POC is processed by microbes, zooplankton and their consumers into fecal pellets, organic aggregates ("marine snow") and other forms, which are thereafter exported to the [[mesopelagic]] (200–1000 m depth) and [[bathypelagic zone]]s by sinking and vertical migration by zooplankton and fish.<ref name=Turner2015 /> Although primary production includes both [[Dissolved organic carbon|dissolved]] and [[particulate organic carbon]] (DOC and POC respectively), only POC leads to efficient carbon export to the ocean interior, whereas the DOC fraction in surface waters is mostly recycled by bacteria.<ref name=Kim2011>{{cite journal |doi = 10.1029/2011GL047346|title = Shifts in biogenic carbon flow from particulate to dissolved forms under high carbon dioxide and warm ocean conditions|year = 2011|last1 = Kim|first1 = Ja-Myung|last2 = Lee|first2 = Kitack|last3 = Shin|first3 = Kyungsoon|last4 = Yang|first4 = Eun Jin|last5 = Engel|first5 = Anja|last6 = Karl|first6 = David M.|last7 = Kim|first7 = Hyun-Cheol|journal = Geophysical Research Letters|volume = 38|issue = 8|pages = n/a|bibcode = 2011GeoRL..38.8612K|doi-access = free}}</ref> However, a more biologically resistant DOC fraction produced in the euphotic zone (accounting for 15–20% of net community productivity), is not immediately mineralized by microbes and accumulates in the ocean surface as biologically [[semi-labile DOC]].<ref>{{cite journal |doi = 10.5670/oceanog.2009.109|title = Dissolved Organic Matter in the Ocean: A Controversy Stimulates New Insights|year = 2009|last1 = Hansell|first1 = Dennis|last2 = Carlson|first2 = Craig|last3 = Repeta|first3 = Daniel|last4 = Schlitzer|first4 = Reiner|journal = Oceanography|volume = 22|issue = 4|pages = 202–211|doi-access = free|hdl = 1912/3183|hdl-access = free}}</ref> This semi-labile DOC undergoes net export to the deep ocean, thus constituting a dynamic part of the biological carbon pump.<ref>{{cite journal |doi = 10.1038/371405a0|title = Annual flux of dissolved organic carbon from the euphotic zone in the northwestern Sargasso Sea|year = 1994|last1 = Carlson|first1 = Craig A.|last2 = Ducklow|first2 = Hugh W.|last3 = Michaels|first3 = Anthony F.|journal = Nature|volume = 371|issue = 6496|pages = 405–408|bibcode = 1994Natur.371..405C|s2cid = 4279712}}</ref> The efficiency of DOC production and export varies across oceanographic regions, being more prominent in the [[oligotrophic]] subtropical oceans.<ref>{{cite journal |doi = 10.1038/s41467-017-02227-3|title = Efficient dissolved organic carbon production and export in the oligotrophic ocean|year = 2017|last1 = Roshan|first1 = Saeed|last2 = Devries|first2 = Timothy|journal = Nature Communications|volume = 8|issue = 1|page = 2036|pmid = 29230041|pmc = 5725454|bibcode = 2017NatCo...8.2036R}}</ref> The overall efficiency of the biological carbon pump is mostly controlled by the export of POC.<ref name=Kim2011 /><ref name=Basu2018 />

===Marine snow===
[[File:Phytoplankton and the biological carbon pump.webp|thumb|upright=2.2|right| {{center|'''Marine snow, phytoplankton and the biological pump{{hsp}}<ref name=Basu2018>{{cite journal |doi = 10.3390/su10030869|title = Phytoplankton as Key Mediators of the Biological Carbon Pump: Their Responses to a Changing Climate|journal = Sustainability|year = 2018|volume = 10|issue = 3|page = 869|doi-access = free|last1 = Basu|first1 = Samarpita|last2 = MacKey|first2 = Katherine}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>'''}} Budget calculations of the biological carbon pump are based on the ratio between [[Marine sediment|sedimentation]] (carbon export) and [[remineralization]] (release to the atmosphere).<ref name=Ionescu2015 />]]
{{main|Marine snow}}
{{see also|Martin curve}}

Most carbon incorporated in organic and inorganic biological matter is formed at the sea surface where it can then start sinking to the ocean floor. The deep ocean gets most of its nutrients from the higher water column when they  sink down in the form of marine snow. This is made up of dead or dying animals and microbes, fecal matter, sand and other inorganic material.<ref name=Steinberg2002>{{cite journal | last=Steinberg | first= Deborah |author2=Sarah Goldthwait |author3=Dennis Hansell  |year=2002 | title=Zooplankton vertical migration and the active transport of dissolved organic and inorganic nitrogen in the Sargasso Sea| journal=Deep-Sea Research Part I| volume=49 | pages=1445–1461 | issn=0967-0637 | doi=10.1016/S0967-0637(02)00037-7 | issue=8 | citeseerx= 10.1.1.391.7622 | bibcode= 2002DSRI...49.1445S }}</ref> A single phytoplankton cell has a sinking rate around one metre per day. Given that the average depth of the ocean is about four kilometres, it can take over ten years for these cells to reach the ocean floor. However, through processes such as coagulation and expulsion in predator fecal pellets, these cells form aggregates. These aggregates, known as [[marine snow]], have sinking rates orders of magnitude greater than individual cells and complete their journey to the deep in a matter of days.<ref name=DeLaRocha2014 />

In the diagram on the right, [[phytoplankton]] fix CO<sub>2</sub> in the [[euphotic]] zone using solar energy and produce [[particulate organic carbon]] (POC). POC formed in the euphotic zone is processed by microbes, zooplankton and their consumers into organic aggregates (marine snow), which is thereafter exported to the [[mesopelagic]] (200–1000 m depth) and [[bathypelagic zone]]s by sinking and [[Diel vertical migration|vertical migration]] by zooplankton and fish. Export flux is defined as the [[Marine sediment|sedimentation]] out of the surface layer (at approximately 100 m depth) and sequestration flux is the sedimentation out of the mesopelagic zone (at approximately 1000 m depth). A portion of the POC is respired back to CO<sub>2</sub> in the oceanic [[water column]] at depth, mostly by [[heterotrophic]] microbes and zooplankton, thus maintaining a vertical gradient in concentration of [[dissolved inorganic carbon]] (DIC). This deep-ocean DIC returns to the atmosphere on millennial timescales through [[thermohaline circulation]]. Between 1% and 40% of the primary production is exported out of the euphotic zone, which attenuates exponentially towards the base of the mesopelagic zone and only about 1% of the surface production reaches the sea floor.<ref name=Basu2018 /><ref name=Passow2012>{{cite journal |doi = 10.3354/meps09985|title = The biological pump in a high CO2 world|year = 2012|last1 = Passow|first1 = U.|last2 = Carlson|first2 = CA|journal = Marine Ecology Progress Series|volume = 470|pages = 249–271|bibcode = 2012MEPS..470..249P|doi-access = free}}</ref><ref name=Turner2015>{{cite journal |doi = 10.1016/j.pocean.2014.08.005|title = Zooplankton fecal pellets, marine snow, phytodetritus and the ocean's biological pump|year = 2015|last1 = Turner|first1 = Jefferson T.|journal = Progress in Oceanography|volume = 130|pages = 205–248|bibcode = 2015PrOce.130..205T}}</ref>

Of the 50–60 Pg of carbon fixed annually, roughly 10% leaves the surface mixed layer of the oceans, while less than 0.5% of eventually reaches the sea floor.<ref name=DeLaRocha2014 /> Most is retained in regenerated production in the euphotic zone and a significant portion is remineralized in midwater processes during particle sinking. The portion of carbon that leaves the surface mixed layer of the ocean is sometimes considered "sequestered", and essentially removed from contact with the atmosphere for many centuries.<ref name=Passow2012 /> However, work also finds that, in regions such as the [[Southern Ocean]], much of this carbon can quickly (within decades) come back into contact with the atmosphere.<ref>{{cite journal |last1=Robinson |first1=J. |last2=Popova |first2=E.E. |last3=Yool |first3=A. |last4=Srokosz |first4=M.A. |last5=Lampitt |first5=R.S. |last6=Blundell |first6=J.R. |date=2014 |title=How deep is deep enough? Ocean iron fertilization and carbon sequestration in the Southern Ocean |journal=Geophys. Res. Lett. |volume=41 |issue= 7|pages=2489–2495 |doi=10.1002/2013GL058799 |url=http://nora.nerc.ac.uk/id/eprint/507032/1/grl51570_Robinson.pdf |bibcode=2014GeoRL..41.2489R |doi-access=free }}</ref>

Budget calculations of the biological carbon pump are based on the ratio between [[Marine sediment|sedimentation]] (carbon export) and [[remineralization]] (release to the atmosphere).<ref name=Ionescu2015>{{cite journal |doi = 10.1038/srep14706|title = A new tool for long-term studies of POM-bacteria interactions: Overcoming the century-old Bottle Effect|year = 2015|last1 = Ionescu|first1 = Danny|last2 = Bizic-Ionescu|first2 = Mina|last3 = Khalili|first3 = Arzhang|last4 = Malekmohammadi|first4 = Reza|last5 = Morad|first5 = Mohammad Reza|last6 = De Beer|first6 = Dirk|last7 = Grossart|first7 = Hans-Peter|journal = Scientific Reports|volume = 5|page = 14706|pmid = 26435525|pmc = 4592964|bibcode = 2015NatSR...514706I}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> It has been estimated that sinking particles export up to 25% of the carbon captured by phytoplankton in the surface ocean to deeper water layers.<ref>{{cite journal |doi = 10.1126/science.281.5374.200|title = Biogeochemical Controls and Feedbacks on Ocean Primary Production|year = 1998|last1 = Falkowski|first1 = P. G.|last2 = Barber|first2 = R. T.|last3 = Smetacek v|first3 = V.|journal = Science|volume = 281|issue = 5374|pages = 200–206|pmid = 9660741}}</ref> About 20% of this export (5% of surface values) is buried in the ocean sediments{{hsp}}<ref>{{cite journal |doi = 10.1038/nature05885|title = The significance of nitrification for oceanic new production|year = 2007|last1 = Yool|first1 = Andrew|last2 = Martin|first2 = Adrian P.|last3 = Fernández|first3 = Camila|last4 = Clark|first4 = Darren R.|journal = Nature|volume = 447|issue = 7147|pages = 999–1002|pmid = 17581584|bibcode = 2007Natur.447..999Y|s2cid = 4416535}}</ref> mainly due to their mineral ballast.<ref name=Iversen2010 /> During the sinking process, these organic particles are hotspots of microbial activity and represent important loci for organic matter mineralization and nutrient redistribution in the water column.<ref name=Simon12002>{{cite journal |doi = 10.3354/ame028175|title = Microbial ecology of organic aggregates in aquatic ecosystems|year = 2002|last1 = Simon|first1 = M.|last2 = Grossart|first2 = HP|last3 = Schweitzer|first3 = B.|last4 = Ploug|first4 = H.|journal = Aquatic Microbial Ecology|volume = 28|pages = 175–211|doi-access = free}}</ref><ref>{{cite journal |doi = 10.3354/meps010257|title = The Ecological Role of Water-Column Microbes in the Sea|year = 1983|last1 = Azam|first1 = F.|last2 = Fenchel|first2 = T.|last3 = Field|first3 = JG|last4 = Gray|first4 = JS|last5 = Meyer-Reil|first5 = LA|last6 = Thingstad|first6 = F.|journal = Marine Ecology Progress Series|volume = 10|pages = 257–263|bibcode = 1983MEPS...10..257A|doi-access = free}}</ref><ref name=Ionescu2015 />

===Biomineralization===

====Ballast minerals====
{{biomineralization sidebar}}

Observations have shown that fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and organic carbon fluxes are closely correlated in the [[bathypelagic zone]]s of the ocean.<ref name=Iversen2010 /> A large fraction of particulate organic matter occurs in the form of marine snow aggregates (>0.5&nbsp;mm) composed of phytoplankton, detritus, inorganic mineral grains, and fecal pellets in the ocean.<ref>{{cite journal |doi = 10.1016/0079-6611(88)90053-5|title = Characteristics, dynamics and significance of marine snow|year = 1988|last1 = Alldredge|first1 = Alice L.|last2 = Silver|first2 = Mary W.|journal = Progress in Oceanography|volume = 20|issue = 1|pages = 41–82|bibcode = 1988PrOce..20...41A}}</ref> Formation and sinking of these aggregates drive the biological carbon pump via export and sedimentation of organic matter from the surface mixed layer to the deep ocean and sediments. The fraction of organic matter that leaves the upper mixed layer of the ocean is, among other factors, determined by the sinking velocity and microbial [[remineralisation]] rate of these aggregates. Recent observations have shown that the fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and the organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. This has led to the hypothesis that organic carbon export is determined by the presence of ballast minerals within settling aggregates.<ref name=Armstrong2002>{{cite journal |doi = 10.1016/S0967-0645(01)00101-1|title = A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals|year = 2001|last1 = Armstrong|first1 = Robert A.|last2 = Lee|first2 = Cindy|last3 = Hedges|first3 = John I.|last4 = Honjo|first4 = Susumu|last5 = Wakeham|first5 = Stuart G.|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 49|issue = 1–3|pages = 219–236|bibcode = 2001DSRII..49..219A}}</ref><ref name=Francois2002>{{cite journal |doi = 10.1029/2001GB001722|title = Factors controlling the flux of organic carbon to the bathypelagic zone of the ocean|year = 2002|last1 = Francois|first1 = Roger|last2 = Honjo|first2 = Susumu|last3 = Krishfield|first3 = Richard|last4 = Manganini|first4 = Steve|journal = Global Biogeochemical Cycles|volume = 16|issue = 4|pages = 34-1-34-20|bibcode = 2002GBioC..16.1087F| s2cid=128876389 |doi-access = free}}</ref><ref name=Klaas2002>{{cite journal |doi = 10.1029/2001GB001765|title = Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio|year = 2002|last1 = Klaas|first1 = Christine|last2 = Archer|first2 = David E.|journal = Global Biogeochemical Cycles|volume = 16|issue = 4|pages = 63-1-63-14|bibcode = 2002GBioC..16.1116K|doi-access = free}}</ref><ref name=Iversen2010>{{cite journal |doi = 10.5194/bgd-7-3335-2010|title = Ballast minerals and the sinking carbon flux in the ocean: Carbon-specific respiration rates and sinking velocities of macroscopic organic aggregates (Marine snow)|last1 = Iversen|first1 = M. H.|last2 = Ploug|first2 = H.|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License].</ref>

Mineral ballasting is associated with about 60% of the flux of particulate organic carbon (POC) in the high-latitude North Atlantic, and with about 40% of the flux in the Southern Ocean.<ref>{{cite journal |doi = 10.1002/2014GL061678|title = Where is mineral ballast important for surface export of particulate organic carbon in the ocean?|year = 2014|last1 = Le Moigne|first1 = Frédéric A. C.|last2 = Pabortsava|first2 = Katsiaryna|last3 = Marcinko|first3 = Charlotte L. J.|last4 = Martin|first4 = Patrick|last5 = Sanders|first5 = Richard J.|journal = Geophysical Research Letters|volume = 41|issue = 23|pages = 8460–8468|pmid = 26074644|pmc = 4459180|bibcode = 2014GeoRL..41.8460L}}</ref> Strong correlations exist also in the deep ocean between the presence of ballast minerals and the flux of POC. This suggests ballast minerals enhance POC flux by increasing the sink rate of ballasted aggregates. Ballast minerals could additionally provide aggregated organic matter some protection from degradation.<ref>{{cite journal |doi = 10.1016/j.marchem.2015.04.009|title = Ballasting effects of smectite on aggregate formation and export from a natural plankton community|year = 2015|last1 = Iversen|first1 = Morten H.|last2 = Robert|first2 = Maya L.|journal = Marine Chemistry|volume = 175|pages = 18–27| bibcode=2015MarCh.175...18I }}</ref>

It has been proposed that organic carbon is better preserved in sinking particles due to increased aggregate density and sinking velocity when ballast minerals are present and/or via protection of the organic matter due to quantitative association to ballast minerals.<ref name=Armstrong2002 /><ref name=Francois2002 /><ref name=Klaas2002 /> In 2002, Klaas and Archer observed that about 83% of the global particulate organic carbon (POC) fluxes were associated with [[carbonate]], and suggested carbonate was a more efficient ballast mineral as compared to opal and terrigenous material. They hypothesized that the higher density of calcium carbonate compared to that of opal and the higher abundance of calcium carbonate relative to terrigenous material might be the reason for the efficient ballasting by calcium carbonate. However, the direct effects of ballast minerals on sinking velocity and degradation rates in sinking aggregates are still unclear.<ref name=Klaas2002 /><ref name=Iversen2010 />

A 2008 study demonstrated copepod fecal pellets produced on a diet of diatoms or coccolithophorids show higher sinking velocities as compared to pellets produced on a nanoflagellate diet.<ref name=Ploug2008>{{cite journal |doi = 10.4319/lo.2008.53.2.0469|title = Production, oxygen respiration rates, and sinking velocity of copepod fecal pellets: Direct measurements of ballasting by opal and calcite|year = 2008|last1 = Ploug|first1 = Helle|last2 = Iversen|first2 = Morten Hvitfeldt|last3 = Koski|first3 = Marja|last4 = Buitenhuis|first4 = Erik Theodoor|journal = Limnology and Oceanography|volume = 53|issue = 2|pages = 469–476|bibcode = 2008LimOc..53..469P|doi-access = free}}</ref> Carbon-specific respiration rates in pellets, however, were similar and independent of mineral content. These results suggest differences in mineral composition do not lead to differential protection of POC against microbial degradation, but the enhanced sinking velocities may result in up to 10-fold higher carbon preservation in pellets containing [[biogenic mineral]]s as compared to that of pellets without biogenic minerals<ref name=Ploug2008 /><ref name=Iversen2010 />

Minerals seem to enhance the [[flocculation]] of phytoplankton aggregates{{hsp}}<ref name=Engel2009a>{{cite journal |doi = 10.1016/j.dsr2.2008.11.028|title = Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi, II: Decomposition of particulate organic matter|year = 2009|last1 = Engel|first1 = Anja|last2 = Abramson|first2 = Lynn|last3 = Szlosek|first3 = Jennifer|last4 = Liu|first4 = Zhanfei|last5 = Stewart|first5 = Gillian|last6 = Hirschberg|first6 = David|last7 = Lee|first7 = Cindy|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 56|issue = 18|pages = 1408–1419|bibcode = 2009DSRII..56.1408E}}</ref><ref name=Engel2009b>{{cite journal |doi = 10.1016/j.dsr2.2008.11.027|title = Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi: I. Formation, settling velocities and physical properties of aggregates|year = 2009|last1 = Engel|first1 = Anja|last2 = Szlosek|first2 = Jennifer|last3 = Abramson|first3 = Lynn|last4 = Liu|first4 = Zhanfei|last5 = Lee|first5 = Cindy|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 56|issue = 18|pages = 1396–1407|bibcode = 2009DSRII..56.1396E}}</ref> and may even act as a catalyst in aggregate formation.<ref>{{cite journal |doi = 10.1016/j.dsr2.2008.11.029|title = Particulate organic matter and ballast fluxes measured using time-series and settling velocity sediment traps in the northwestern Mediterranean Sea|year = 2009|last1 = Lee|first1 = Cindy|last2 = Peterson|first2 = Michael L.|last3 = Wakeham|first3 = Stuart G.|last4 = Armstrong|first4 = Robert A.|last5 = Cochran|first5 = J. Kirk|last6 = Miquel|first6 = Juan Carlos|last7 = Fowler|first7 = Scott W.|last8 = Hirschberg|first8 = David|last9 = Beck|first9 = Aaron|last10 = Xue|first10 = Jianhong|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 56|issue = 18|pages = 1420–1436|bibcode = 2009DSRII..56.1420L}}</ref> However, it has also been shown that incorporation of minerals can cause aggregates to fragment into smaller and denser aggregates.<ref name=Passow2006>{{cite journal |doi = 10.1029/2005GB002579|title = Accumulation of mineral ballast on organic aggregates|year = 2006|last1 = Passow|first1 = Uta|last2 = de la Rocha|first2 = Christina L.|journal = Global Biogeochemical Cycles|volume = 20|issue = 1|pages = n/a|bibcode = 2006GBioC..20.1013P|doi-access = free}}</ref> This can potentially lower the sinking velocity of the aggregated organic material due to the reduced aggregate sizes, and, thus, lower the total export of organic matter. Conversely, if the incorporation of minerals increases the aggregate density, its size-specific sinking velocity may also increase, which could potentially increase the carbon export. Therefore, there is still a need for better quantitative investigations of how the interactions between minerals and organic aggregates affect the degradation and sinking velocity of the aggregates and, hence, carbon sequestration in the ocean.<ref name=Passow2006 /><ref name=Iversen2010 />

====Remineralisation====
[[Remineralisation]]  refers to the breakdown or transformation of [[organic matter]] (those molecules derived from a biological source) into its simplest [[Inorganic compound|inorganic]] forms. These transformations form a crucial link within [[ecosystem]]s as they are responsible for liberating the energy stored in [[Organic compound|organic molecules]] and recycling matter within the system to be reused as [[nutrient]]s by other [[organism]]s.<ref name=Sarmiento2013 /> What fraction does escape remineralisation varies depending on the location. For example, in the North Sea, values of carbon deposition are ~1% of primary production<ref>{{cite journal |last1=Thomas |first1=Helmuth |last2=Bozec |first2=Yann |last3=Elkalay |first3=Khalid |last4=Baar |first4=Hein J. W. de |date=14 May 2004 |title=Enhanced Open Ocean Storage of CO2 from Shelf Sea Pumping |journal=Science |language=en |volume=304 |issue=5673 |pages=1005–1008 |doi=10.1126/science.1095491 |issn=0036-8075 |pmid=15143279 |bibcode=2004Sci...304.1005T|hdl=11370/e821600e-4560-49e8-aeec-18eeb17549e3 |s2cid=129790522 |url=https://pure.rug.nl/ws/files/9825939/2004ScienceThomas.pdf |hdl-access=free }}</ref> while that value is <0.5% in the open oceans on average.<ref>{{cite book |last=De La Rocha |first=C. L. |title=Treatise on Geochemistry |date=2006 |chapter=The Biological Pump |volume=6 |page=625 |editor1-last=Holland |editor1-first=Heinrich D. |editor2-last=Turekian |editor2-first=Karl K. |publisher=Pergamon Press |doi=10.1016/B0-08-043751-6/06107-7 |isbn=978-0-08-043751-4 |bibcode=2003TrGeo...6...83D}}</ref>  Therefore, most of nutrients remain in the water column, recycled by the [[Biota (ecology)|biota]]. [[Heterotroph]]ic organisms will utilize the materials produced by the [[autotroph]]ic (and [[chemotroph]]ic) organisms and via respiration will remineralise the compounds from the organic form back to inorganic, making them available for primary producers again.

For most areas of the ocean, the highest rates of carbon remineralisation occur at depths between {{convert|100|-|1200|m|ft|abbr=on}} in the water column, decreasing down to about {{convert|1,200|m|ft|abbr=on}} where remineralisation rates remain pretty constant at 0.1 μmol kg<sup>−1</sup> yr<sup>−1</sup>.<ref>{{cite journal |last1=Feely |first1=Richard A. |last2=Sabine |first2=Christopher L. |last3=Schlitzer |first3=Reiner |last4=Bullister |first4=John L. |last5=Mecking |first5=Sabine |last6=Greeley |first6=Dana |date=1 February 2004 |title=Oxygen Utilization and Organic Carbon Remineralisation in the Upper Water Column of the Pacific Ocean |journal=Journal of Oceanography |language=en |volume=60 |issue=1 |pages=45–52 |doi=10.1023/B:JOCE.0000038317.01279.aa |bibcode=2004JOce...60...45F |s2cid=67846685 |issn=0916-8370}}</ref> This provides the most nutrients available for primary producers within the photic zone, though it leaves the upper surface waters starved of inorganic nutrients.<ref>{{cite web| url = http://oceanservice.noaa.gov/facts/light_travel.html| title = How far does light travel in the ocean?| last = Administration| first = US Department of Commerce, National Oceanic and Atmospheric| website = oceanservice.noaa.gov| language = EN-US| access-date = 2016-02-29}}</ref> Most remineralisation is done with [[dissolved organic carbon]] (DOC). Studies have shown that it is larger sinking particles that transport matter down to the sea floor<ref>{{cite journal |last1=Karl |first1=David M. |last2=Knauer |first2=George A. |last3=Martin |first3=John H. |date=1 March 1988 |title=Downward flux of particulate organic matter in the ocean: a particle decomposition paradox |bibcode=1988Natur.332..438K |journal=Nature |volume=332 |issue=6163 |pages=438–441 |doi=10.1038/332438a0 |s2cid=4356597 |issn=0028-0836}}</ref> while suspended particles and dissolved organics are mostly consumed by remineralisation.<ref>{{cite journal |last1=Lefévre |first1=D. |last2=Denis |first2=M. |last3=Lambert |first3=C. E. |last4=Miquel |first4=J. -C. |date=1 February 1996 |title=Is DOC the main source of organic matter remineralization in the ocean water column? |journal=Journal of Marine Systems |series=The Coastal Ocean in a Global Change Perspective |volume=7 |issue=2–4 |pages=281–291 |doi=10.1016/0924-7963(95)00003-8 |bibcode=1996JMS.....7..281L}}</ref> This happens in part due to the fact that organisms must typically ingest nutrients smaller than they are, often by orders of magnitude.<ref>{{cite book |url=https://books.google.com/books?id=T5trCQAAQBAJ |title=Biodiversity and Ecosystem Function |last1=Schulze |first1=Ernst-Detlef |last2=Mooney |first2=Harold A. |date=6 December 2012 |publisher=Springer Science & Business Media |isbn=978-3-642-58001-7 |language=en}}</ref> With the microbial community making up 90% of marine biomass,<ref>{{cite web |url=http://www.coml.org/projects/international-census-marine-microbes-icomm |title=International Census of Marine Microbes (ICoMM) |series=Census of Marine Life |website=www.coml.org |access-date=29 February 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160317223727/http://www.coml.org/projects/international-census-marine-microbes-icomm |archive-date=17 March 2016 }}</ref> it is particles smaller than the microbes (on the order of {{10^|-6}}) that will be taken up for remineralisation.<ref>{{cite web |url=https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/microscopy-3/looking-at-microbes-28/microbe-size-238-4283/ |title=Microbe Size - Boundless Open Textbook |website=Boundless |access-date=29 February 2016}}</ref>

===Key role of phytoplankton===
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 | caption1  = {{center| Glass shell ([[frustule]]) of a [[diatom]]}}
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 | caption2  = {{center| [[Coccolithophores]] help power the carbonate pump by producing hard structures out of calcium carbonate which eventually sink to the ocean floor}}
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{{biogeochemical cycle sidebar|marine}}

Marine phytoplankton perform half of all photosynthesis on Earth{{hsp}}<ref name="The role of temperature, cellular q">{{cite journal |doi = 10.1016/j.limno.2008.06.002|title = The role of temperature, cellular quota and nutrient concentrations for photosynthesis, growth and light–dark acclimation in phytoplankton|year = 2008|last1 = Baumert|first1 = Helmut Z.|last2 = Petzoldt|first2 = Thomas|journal = Limnologica|volume = 38|issue = 3–4|pages = 313–326|doi-access = | bibcode=2008Limng..38..313B }}</ref> and directly influence global biogeochemical cycles and the climate, yet how they will respond to future global change is unknown. Carbon dioxide is one of the principal drivers of global change and has been identified as one of the major challenges in the 21st century.<ref>{{cite journal |doi = 10.1016/j.ijggc.2012.07.010|title = Current status and challenges on microalgae-based carbon capture|year = 2012|last1 = Lam|first1 = Man Kee|last2 = Lee|first2 = Keat Teong|last3 = Mohamed|first3 = Abdul Rahman|journal = International Journal of Greenhouse Gas Control|volume = 10|pages = 456–469| bibcode=2012IJGGC..10..456L }}</ref> Carbon dioxide (CO<sub>2</sub>) generated during anthropogenic activities such as deforestation and burning of fossil fuels for energy generation rapidly dissolves in the surface ocean and lowers seawater pH, while CO<sub>2</sub> remaining in the atmosphere increases global temperatures and leads to increased [[Ocean stratification|ocean thermal stratification]]. While CO<sub>2</sub> concentration in the atmosphere is estimated to be about 270 [[Parts per million|ppm]] before the industrial revolution, it has currently increased to about 400 ppm{{hsp}}<ref name="Häder2014">{{cite journal |doi = 10.1039/C3PP50418B|title = Productivity of aquatic primary producers under global climate change|year = 2014|last1 = Häder|first1 = Donat-P.|last2 = Villafañe|first2 = Virginia E.|last3 = Helbling|first3 = E. Walter|journal = Photochem. Photobiol. Sci.|volume = 13|issue = 10|pages = 1370–1392|pmid = 25191675| s2cid=25740029 |doi-access = free|hdl = 11336/24725|hdl-access = free}}</ref> and is expected to reach 800–1000 ppm by the end of this century according to the "business as usual" CO<sub>2</sub> emission scenario.<ref name=Li2012>{{cite journal |doi = 10.1371/journal.pone.0051590|title = Interactive Effects of Ocean Acidification and Nitrogen-Limitation on the Diatom Phaeodactylum tricornutum|year = 2012|last1 = Li|first1 = Wei|last2 = Gao|first2 = Kunshan|last3 = Beardall|first3 = John|journal = PLOS ONE|volume = 7|issue = 12|pages = e51590|pmid = 23236517|pmc = 3517544|bibcode = 2012PLoSO...751590L|doi-access = free}}</ref><ref name=Basu2018 />

Marine ecosystems are a major sink for atmospheric CO<sub>2</sub> and take up similar amount of CO<sub>2</sub> as terrestrial ecosystems, currently accounting for the removal of nearly one third of anthropogenic CO<sub>2</sub> emissions from the atmosphere.<ref name="Häder2014" /><ref name=Li2012 /> The net transfer of CO<sub>2</sub> from the atmosphere to the oceans and then [[Marine sediment|sediments]], is mainly a direct consequence of the combined effect of the solubility and the biological pump.<ref name="Hülse2017">{{cite journal |doi = 10.1016/j.earscirev.2017.06.004|title = Understanding the causes and consequences of past marine carbon cycling variability through models|year = 2017|last1 = Hülse|first1 = Dominik|last2 = Arndt|first2 = Sandra|last3 = Wilson|first3 = Jamie D.|last4 = Munhoven|first4 = Guy|last5 = Ridgwell|first5 = Andy|journal = Earth-Science Reviews|volume = 171|pages = 349–382|bibcode = 2017ESRv..171..349H| hdl=1983/7035f071-71c5-48a5-91f6-a8286e386d21 |url = https://research-information.bris.ac.uk/ws/files/134880543/BioPumpInEMICS.pdf}}</ref> While the [[solubility pump]] serves to concentrate [[dissolved inorganic carbon]] (CO<sub>2</sub> plus bicarbonate and carbonate ions) in the deep oceans, the biological carbon pump (a key natural process and a major component of the global carbon cycle that regulates atmospheric CO<sub>2</sub> levels) transfers both organic and inorganic carbon fixed by [[Marine primary production|primary producers]] (phytoplankton) in the [[euphotic zone]] to the ocean interior and subsequently to the underlying sediments.<ref name="Hülse2017" /><ref name=Chisholm1995>{{cite journal |doi = 10.1029/95RG00743|title = The iron hypothesis: Basic research meets environmental policy|year = 1995|last1 = Chisholm|first1 = Sallie W.|journal = Reviews of Geophysics|volume = 33|issue = S2|pages = 1277–1286|bibcode = 1995RvGeo..33S1277C}}</ref> Thus, the biological pump takes carbon out of contact with the atmosphere for several thousand years or longer and maintains atmospheric CO<sub>2</sub> at significantly lower levels than would be the case if it did not exist.<ref>{{cite journal |doi = 10.1038/nmicrobiol.2017.58|title = Microorganisms and ocean global change|year = 2017|last1 = Hutchins|first1 = David A.|last2 = Fu|first2 = Feixue|journal = Nature Microbiology|volume = 2|issue = 6|page = 17058|pmid = 28540925|s2cid = 23357501}}</ref> An ocean without a biological pump, which transfers roughly 11 [[Gigatonne|Gt]] C yr<sup>−1</sup> into the ocean's interior, would result in atmospheric CO<sub>2</sub> levels ~400 ppm higher than present day.<ref>{{cite journal |doi = 10.1016/j.pocean.2014.05.005|title = The Biological Carbon Pump in the North Atlantic|year = 2014|last1 = Sanders|first1 = Richard|last2 = Henson|first2 = Stephanie A.|last3 = Koski|first3 = Marja|last4 = de la Rocha|first4 = Christina L.|last5 = Painter|first5 = Stuart C.|last6 = Poulton|first6 = Alex J.|last7 = Riley|first7 = Jennifer|last8 = Salihoglu|first8 = Baris|last9 = Visser|first9 = Andre|last10 = Yool|first10 = Andrew|last11 = Bellerby|first11 = Richard|last12 = Martin|first12 = Adrian P.|journal = Progress in Oceanography|volume = 129|pages = 200–218|bibcode = 2014PrOce.129..200S}}</ref><ref>{{cite journal |doi = 10.3389/fmars.2015.00077|title = Toward quantifying the response of the oceans' biological pump to climate change|year = 2015|last1 = Boyd|first1 = Philip W.|journal = Frontiers in Marine Science|volume = 2|s2cid = 16787695|doi-access = free}}</ref><ref name=Basu2018 />

Passow and Carlson defined sedimentation out of the surface layer (at approximately 100 m depth) as the "export flux" and that out of the [[mesopelagic zone]] (at approximately 1000 m depth) as the "sequestration flux".<ref name=Passow2012 /> Once carbon is transported below the mesopelagic zone, it remains in the deep sea for 100 years or longer, hence the term "sequestration" flux. According to the modelling results of Buesseler and Boyd between 1% and 40% of the primary production is exported out of the euphotic zone,<ref name=Buesseler2009>{{cite journal |doi = 10.4319/lo.2009.54.4.1210|title = Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean|year = 2009|last1 = Buesseler|first1 = Ken O.|last2 = Boyd|first2 = Philip W.|journal = Limnology and Oceanography|volume = 54|issue = 4|pages = 1210–1232|bibcode = 2009LimOc..54.1210B|doi-access = free}}</ref> which attenuates exponentially towards the base of the mesopelagic zone and only about 1% of the surface production reaches the sea floor.<ref name=Herndl2013 /> The export efficiency of [[particulate organic carbon]] (POC) shows regional variability. For instance, in the North Atlantic, over 40% of net primary production is exported out of the euphotic zone as compared to only 10% in the South Pacific,<ref name=Buesseler2009 /> and this is driven in part by the composition of the phytoplankton community including cell size and composition (see below). Exported organic carbon is remineralized, that is, respired back to CO<sub>2</sub> in the oceanic water column at depth, mainly by heterotrophic microbes and zooplankton. Thus, the biological carbon pump maintains a vertical gradient in the concentration of [[dissolved inorganic carbon]] (DIC), with higher values at increased ocean depth.<ref>{{cite journal |doi = 10.1073/pnas.0813384106|title = Oceanic acidification affects marine carbon pump and triggers extended marine oxygen holes|year = 2009|last1 = Hofmann|first1 = M.|last2 = Schellnhuber|first2 = H.-J.|journal = Proceedings of the National Academy of Sciences|volume = 106|issue = 9|pages = 3017–3022|pmid = 19218455|pmc = 2642667|bibcode = 2009PNAS..106.3017H|doi-access = free}}</ref> This deep-ocean DIC returns to the atmosphere on millennial timescales through [[thermohaline circulation]].<ref name=Ducklow2001>{{cite journal |doi = 10.5670/oceanog.2001.06|title = Upper Ocean Carbon Export and the Biological Pump|year = 2001|last1 = Ducklow|first1 = Hugh|last2 = Steinberg|first2 = Deborah|last3 = Buesseler|first3 = Ken|journal = Oceanography|volume = 14|issue = 4|pages = 50–58|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><ref name=Basu2018 />

In 2001, Hugh et al. expressed the efficiency of the biological pump as the amount of carbon exported from the surface layer (export production) divided by the total amount produced by photosynthesis (overall production).<ref name=Ducklow2001 /> Modelling studies by Buesseler and Boyd revealed that the overall transfer efficiency of the biological pump is determined by a combination of factors: seasonality;<ref name=Buesseler2009 /> the composition of phytoplankton species; the fragmentation of particles by zooplankton; and the solubilization of particles by microbes. In addition, the efficiency of the biological pump is also dependent on the aggregation and disaggregation of organic-rich aggregates and interaction between POC aggregates and suspended "ballast" minerals.<ref>{{cite journal |doi = 10.1016/j.dsr2.2007.01.004|title = Factors influencing the sinking of POC and the efficiency of the biological carbon pump|year = 2007|last1 = de la Rocha|first1 = Christina L.|last2 = Passow|first2 = Uta|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 54|issue = 5–7|pages = 639–658|bibcode = 2007DSRII..54..639D|url = https://epic.awi.de/id/eprint/14896/1/DeL2006a.pdf}}</ref> Ballast minerals (silicate and carbonate biominerals and dust) are the major constituents of particles that leave the ocean surface via sinking. They are typically denser than seawater and most organic matter, thus, providing a large part of the density differential needed for sinking of the particles.<ref name="Armstrong2002"/> Aggregation of particles increases vertical flux by transforming small suspended particles into larger, rapidly-sinking ones. It plays an important role in the sedimentation of phytodetritus from surface layer phytoplankton blooms.<ref name=Turner2015 /> As illustrated by Turner in 2015, the vertical flux of sinking particles is mainly due to a combination of fecal pellets, marine snow and direct sedimentation of phytoplankton blooms, which are typically composed of diatoms, coccolithophorids, dinoflagellates and other plankton.<ref name=Turner2015 /> Marine snow comprises macroscopic organic aggregates >500&nbsp;μm in size and originates from clumps of aggregated phytoplankton (phytodetritus), discarded appendicularian houses, fecal matter and other miscellaneous detrital particles,<ref name=Turner2015 /> Appendicularians secrete mucous feeding structures or "houses" to collect food particles and discard and renew them up to 40 times a day .<ref>{{cite journal |doi = 10.3354/meps259163|title = Species-specific house productivity of appendicularians|year = 2003|last1 = Sato|first1 = R.|last2 = Tanaka|first2 = Y.|last3 = Ishimaru|first3 = T.|journal = Marine Ecology Progress Series|volume = 259|pages = 163–172|bibcode = 2003MEPS..259..163S|doi-access = free}}</ref> Discarded appendicularian houses are highly abundant (thousands per m3 in surface waters) and are microbial hotspots with high concentrations of bacteria, ciliates, flagellates and phytoplankton. These discarded houses are therefore among the most important sources of aggregates directly produced by zooplankton in terms of carbon cycling potential.<ref>{{cite journal |doi = 10.1002/lno.10061|title = Degradation of discarded appendicularian houses by oncaeid copepods|year = 2015|last1 = Nishibe|first1 = Yuichiro|last2 = Takahashi|first2 = Kazutaka|last3 = Ichikawa|first3 = Tadafumi|last4 = Hidaka|first4 = Kiyotaka|last5 = Kurogi|first5 = Hiroaki|last6 = Segawa|first6 = Kyohei|last7 = Saito|first7 = Hiroaki|journal = Limnology and Oceanography|volume = 60|issue = 3|pages = 967–976|bibcode = 2015LimOc..60..967N|doi-access = }}</ref><ref name=Basu2018 />

[[File:Cyanothece sp. ATCC 51142 cell.jpg|thumb| The nitrogen fixing cyanobacteria ''[[Cyanothece]]'' sp. ATCC 51142]]

The composition of the phytoplankton community in the euphotic zone largely determines the quantity and quality of organic matter that sinks to depth.<ref name=Herndl2013>{{cite journal |doi = 10.1038/ngeo1921|title = Microbial control of the dark end of the biological pump|year = 2013|last1 = Herndl|first1 = Gerhard J.|last2 = Reinthaler|first2 = Thomas|journal = Nature Geoscience|volume = 6|issue = 9|pages = 718–724|pmid = 24707320|pmc = 3972885|bibcode = 2013NatGe...6..718H}}</ref> The main functional groups of marine phytoplankton that contribute to export production include [[nitrogen fixation|nitrogen fixers]] ([[diazotrophic]] [[cyanobacteria]]), [[silicifier]]s (diatoms) and [[calcifier]]s (coccolithophores). Each of these phytoplankton groups differ in the size and composition of their cell walls and coverings, which influence their sinking velocities.<ref name=Collins2013>{{cite journal |doi = 10.1111/eva.12120|title = Evolutionary potential of marine phytoplankton under ocean acidification|year = 2014|last1 = Collins|first1 = Sinéad|last2 = Rost|first2 = Björn|last3 = Rynearson|first3 = Tatiana A.|author-link3=Tatiana Rynearson|journal = Evolutionary Applications|volume = 7|issue = 1|pages = 140–155|pmid = 24454553|pmc = 3894903| bibcode=2014EvApp...7..140C }}</ref> For example, autotrophic picoplankton (0.2–2&nbsp;μm in diameter)—which include taxa such as cyanobacteria (e.g., ''[[Prochlorococcus]]'' spp. and ''[[Synechococcus]]'' spp.) and [[prasinophyte]]s (various genera of eukaryotes <2&nbsp;μm)—are believed to contribute much less to carbon export from surface layers due to their small size, slow sinking velocities (<0.5 m/day) and rapid turnover in the microbial loop.<ref name=Collins2013 /><ref name=Richardson2007>{{cite journal |doi = 10.1126/science.1133471|title = Small Phytoplankton and Carbon Export from the Surface Ocean|year = 2007|last1 = Richardson|first1 = T. L.|last2 = Jackson|first2 = G. A.|journal = Science|volume = 315|issue = 5813|pages = 838–840|pmid = 17289995|bibcode = 2007Sci...315..838R|s2cid = 45563491}}</ref> In contrast, larger phytoplankton cells such as diatoms (2–500&nbsp;μm in diameter) are very efficient in transporting carbon to depth by forming rapidly sinking aggregates.<ref name=Passow2012 /> They are unique among phytoplankton, because they require Si in the form of silicic acid (Si(OH)4) for growth and production of their frustules, which are made of biogenic silica (bSiO2) and act as ballast.<ref name=Collins2013 /><ref name=Ragueneau2006>{{cite journal |doi = 10.1029/2006GB002688|title = Si and C interactions in the world ocean: Importance of ecological processes and implications for the role of diatoms in the biological pump|year = 2006|last1 = Ragueneau|first1 = Olivier|last2 = Schultes|first2 = Sabine|last3 = Bidle|first3 = Kay|last4 = Claquin|first4 = Pascal|last5 = Moriceau|first5 = Brivaëla|journal = Global Biogeochemical Cycles|volume = 20|issue = 4|pages = n/a|bibcode = 2006GBioC..20.4S02R|doi-access = free}}</ref> According to the reports of Miklasz and Denny,<ref name=Miklasz2010>{{cite journal |doi = 10.4319/lo.2010.55.6.2513|title = Diatom sinkings speeds: Improved predictions and insight from a modified Stokes' law|year = 2010|last1 = Miklasz|first1 = Kevin A.|last2 = Denny|first2 = Mark W.|journal = Limnology and Oceanography|volume = 55|issue = 6|pages = 2513–2525|bibcode = 2010LimOc..55.2513M|doi-access = free}}</ref> the sinking velocities of diatoms can range from 0.4 to 35 m/day.<ref name=Collins2013 /><ref name=Ragueneau2006 /><ref name=Miklasz2010 /> Analogously, coccolithophores are covered with calcium carbonate plates called 'coccoliths', which are central to aggregation and ballasting, producing sinking velocities of nearly 5 m/day.<ref name=Passow2012 /><ref name=Collins2013 /> Although it has been assumed that [[picophytoplankton]], characterizing vast [[oligotrophic]] areas of the ocean,<ref name=Herndl2013 /> do not contribute substantially to the particulate organic carbon (POC) flux, in 2007 Richardson and Jackson suggested that all phytoplankton, including picoplankton cells, contribute equally to POC export.<ref name=Richardson2007 /> They proposed alternative pathways for picoplankton carbon cycling, which rely on aggregation as a mechanism for both direct sinking (the export of picoplankton as POC) and mesozooplankton- or large filter feeder-mediated sinking of picoplankton-based production.<ref name=Basu2018 />

{{clear}}

===Zooplankton grazing===
{{see also|Zooplankton#Role in biogeochemistry}}

====Sloppy feeding====
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 | caption1  = {{center|'''Sloppy feeding by zooplankton'''<br  />DOC {{=}} [[dissolved organic carbon]]<br  />POC {{=}} [[particulate organic carbon]].<br  /><small>Adapted from Møller et al. (2005),<ref name="Møller2003">{{cite journal |doi = 10.3354/meps262185|title = Production of DOC by ''Calanus finmarchicus'', ''C. Glacialis'' and ''C. Hyperboreus'' through sloppy feeding and leakage from fecal pellets|year = 2003|last1 = Møller|first1 = EF|last2 = Thor|first2 = P.|last3 = Nielsen|first3 = TG|journal = Marine Ecology Progress Series|volume = 262|pages = 185–191|bibcode = 2003MEPS..262..185M|doi-access = free}}</ref> Saba et al. (2009)<ref name=Saba2009>{{cite journal |doi = 10.3354/meps08070|title = Effects of diet on release of dissolved organic and inorganic nutrients by the copepod ''Acartia tonsa''|year = 2009|last1 = Saba|first1 = GK|last2 = Steinberg|first2 = DK|last3 = Bronk|first3 = DA|journal = Marine Ecology Progress Series|volume = 386|pages = 147–161|bibcode = 2009MEPS..386..147S|doi-access = free}}</ref> and Steinberg et al. (2017).<ref name=Steinberg12017>{{cite journal |doi = 10.1146/annurev-marine-010814-015924|title = Zooplankton and the Ocean Carbon Cycle|year = 2017|last1 = Steinberg|first1 = Deborah K.|last2 = Landry|first2 = Michael R.|journal = Annual Review of Marine Science|volume = 9|pages = 413–444|pmid = 27814033|bibcode = 2017ARMS....9..413S}}</ref></small>}}
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 | caption2  = {{center|'''Mesopelagic fecal pellet production'''}} On the left above, intact fecal pellets reach the deep ocean via vertical migration of zooplankton, whereas on the right fecal pellets at depth result from in situ repackaging of sinking detritus by deep-dwelling zooplankton. Actual mechanisms are likely to include both scenarios.<ref name=Belcher2017>{{cite journal |doi = 10.5194/bg-14-1511-2017|title = Copepod faecal pellet transfer through the meso- and bathypelagic layers in the Southern Ocean in spring|year = 2017|last1 = Belcher|first1 = Anna|last2 = Manno|first2 = Clara|last3 = Ward|first3 = Peter|last4 = Henson|first4 = Stephanie A.|last5 = Sanders|first5 = Richard|last6 = Tarling|first6 = Geraint A.|journal = Biogeosciences|volume = 14|issue = 6|pages = 1511–1525|bibcode = 2017BGeo...14.1511B | doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License].</ref>
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[[File:Morphology of copepod faecal pellets.png|thumb|upright=2.1| {{center|'''Morphology of zooplankton fecal pellets{{hsp}}<ref name=Belcher2017 />'''<br />Collected from [[marine snow]] catchers (a–c) and [[sediment trap]]s (d–f).<br />Morphological classes: (a, d) round, (b, e) cylindrical, and (c, f) ovoid.<br /><small>Scale bar {{=}} 0.5 mm</small>}}]]

In addition to linking primary producers to higher trophic levels in marine food webs, zooplankton also play an important role as "recyclers" of carbon and other nutrients that significantly impact marine biogeochemical cycles, including the biological pump. This is particularly the case with [[copepod]]s and [[krill]], and is especially important in oligotrophic waters of the open ocean. Through sloppy feeding, excretion, egestion, and leaching of fecal pellets, zooplankton release dissolved organic matter (DOM) which controls DOM cycling and supports the microbial loop. Absorption efficiency, respiration, and prey size all further complicate how zooplankton are able to transform and deliver carbon to the deep ocean.<ref name=Steinberg12017 />

Excretion and sloppy feeding (the physical breakdown of food source) make up 80% and 20% of crustacean zooplankton-mediated DOM release respectively.<ref name=Saba2011>{{cite journal |doi = 10.1016/j.jembe.2011.04.013|title = The relative importance of sloppy feeding, excretion, and fecal pellet leaching in the release of dissolved carbon and nitrogen by Acartia tonsa copepods|year = 2011|last1 = Saba|first1 = Grace K.|last2 = Steinberg|first2 = Deborah K.|last3 = Bronk|first3 = Deborah A.|journal = Journal of Experimental Marine Biology and Ecology|volume = 404|issue = 1–2|pages = 47–56| bibcode=2011JEMBE.404...47S }}</ref> In the same study, fecal pellet leaching was found to be an insignificant contributor. For protozoan grazers, DOM is released primarily through excretion and egestion and gelatinous zooplankton can also release DOM through the production of mucus. Leaching of fecal pellets can extend from hours to days after initial egestion and its effects can vary depending on food concentration and quality.<ref name=Thor2003>{{cite journal |doi = 10.3354/ame033279|title = Fate of organic carbon released from decomposing copepod fecal pellets in relation to bacterial production and ectoenzymatic activity|year = 2003|last1 = Thor|first1 = P.|last2 = Dam|first2 = HG|last3 = Rogers|first3 = DR|journal = Aquatic Microbial Ecology|volume = 33|pages = 279–288|doi-access = free}}</ref><ref name=Carlso2014>{{Cite book|url=https://books.google.com/books?id=7iKOAwAAQBAJ&q=%22Biogeochemistry+of+marine+dissolved+organic+matter%22|title=Biogeochemistry of Marine Dissolved Organic Matter|isbn=9780124071537|last1=Hansell|first1=Dennis A.|last2=Carlson|first2=Craig A.|date=2 October 2014|publisher=Academic Press }}</ref>  Various factors can affect how much DOM is released from zooplankton individuals or populations.

====Fecal pellets====
The fecal pellets of zooplankton can be important vehicles for the transfer of particulate organic carbon (POC) to the deep ocean, often making large contributions to the carbon sequestration. The size distribution of the copepod community indicates high numbers of small fecal pellets are produced in the [[epipelagic]]. However, small fecal pellets are rare in the deeper layers, suggesting they are not transferred efficiently to depth. This means small fecal pellets make only minor contributions to fecal pellet fluxes in the meso- and bathypelagic, particularly in terms of carbon. In a study is focussed on the [[Scotia Sea]], which contains some of the most productive regions in the Southern Ocean, the dominant fecal pellets in the upper [[mesopelagic]] were cylindrical and elliptical, while [[ovoid]] fecal pellets were dominant in the [[bathypelagic]]. The change in fecal pellet morphology, as well as size distribution, points to the repacking of surface fecal pellets in the mesopelagic and in situ production in the lower meso- and bathypelagic, which may be augmented by inputs of fecal pellets via zooplankton [[Diel vertical migration|vertical migrations]]. This suggests the flux of carbon to the deeper layers within the Southern Ocean is strongly modulated by meso- and bathypelagic zooplankton, meaning that the community structure in these zones has a major impact on the efficiency of the fecal pellet transfer to ocean depths.<ref name=Belcher2017 />

[[Absorption efficiency]] (AE) is the proportion of food absorbed by plankton that determines how available the consumed organic materials are in meeting the required physiological demands.<ref name=Steinberg12017 /> Depending on the feeding rate and prey composition, variations in AE may lead to variations in fecal pellet production, and thus regulates how much organic material is recycled back to the marine environment. Low feeding rates typically lead to high AE and small, dense pellets, while high feeding rates typically lead to low AE and larger pellets with more organic content. Another contributing factor to DOM release is respiration rate. Physical factors such as oxygen availability, pH, and light conditions may affect overall oxygen consumption and how much carbon is loss from zooplankton in the form of respired CO<sub>2</sub>. The relative sizes of zooplankton and prey also mediate how much carbon is released via sloppy feeding. Smaller prey are ingested whole, whereas larger prey may be fed on more "sloppily", that is more biomatter is released through inefficient consumption.<ref name="Møller2005">{{cite journal |doi = 10.1093/plankt/fbh147|title = Sloppy feeding in marine copepods: Prey-size-dependent production of dissolved organic carbon|year = 2004|last1 = Moller|first1 = E. F.|journal = Journal of Plankton Research|volume = 27|pages = 27–35|doi-access = free}}</ref><ref name="Møller2007">{{cite journal |doi = 10.4319/lo.2007.52.1.0079|title = Production of dissolved organic carbon by sloppy feeding in the copepods Acartia tonsa, Centropages typicus, and Temora longicornis|year = 2007|last1 = Møller|first1 = Eva Friis|journal = Limnology and Oceanography|volume = 52|issue = 1|pages = 79–84|bibcode = 2007LimOc..52...79M|doi-access = free}}</ref> There is also evidence that diet composition can impact nutrient release, with carnivorous diets releasing more [[dissolved organic carbon]] (DOC) and ammonium than omnivorous diets.<ref name=Thor2003 />

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===Microbial loop===
[[File:Microbial Loop.jpg|thumb|upright=1.2|The microbial loop is a marine trophic pathway which incorporates [[dissolved organic carbon]] (DOC) into the food chain]]
{{main|Microbial loop}}

====Bacterial lysis====
The [[microbial loop]] describes a trophic pathway in the marine [[microbial food web]] where [[dissolved organic carbon]] (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by [[phytoplankton]]-[[zooplankton]]-[[nekton]]. The term microbial loop was coined by [[Farooq Azam]], [[Tom Fenchel]] et al.<ref name=AzamFenchel1983>{{cite journal |last1=Azam |first1=Farooq |author-link1=Farooq Azam |last2=Fenchel |first2=Tom |author-link2=Tom Fenchel |last3=Field |first3=J.G. |last4=Gray |first4=J.S. |last5=Meyer-Reil |first5=L.A. |last6=Thingstad |first6=F. |title=The Ecological Role of Water-Column Microbes in the Sea |journal=Marine Ecology Progress Series |volume=10 |year=1983 |pages=257–263 |doi=10.3354/meps010257 |bibcode=1983MEPS...10..257A |doi-access=free}}</ref> in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment. In general, dissolved organic carbon is introduced into the ocean environment from [[bacterial lysis]], the leakage or exudation of fixed carbon from phytoplankton (e.g., mucilaginous exopolymer from [[diatom]]s), sudden cell senescence, sloppy feeding by zooplankton, the excretion of waste products by aquatic animals, or the breakdown or dissolution of organic particles from terrestrial plants and soils.<ref name="Van den Meersche Middelburg Soetaert van Rijswijk 2004">{{cite journal | last1=Van den Meersche | first1=Karel | last2=Middelburg | first2=Jack J. | last3=Soetaert | first3=Karline | last4=van Rijswijk | first4=Pieter | last5=Boschker | first5=Henricus T. S. | last6=Heip | first6=Carlo H. R. | title=Carbon-nitrogen coupling and algal-bacterial interactions during an experimental bloom: Modeling a13C tracer experiment | journal=Limnology and Oceanography | volume=49 | issue=3 | year=2004 | issn=0024-3590 | doi=10.4319/lo.2004.49.3.0862 | pages=862–878| bibcode=2004LimOc..49..862V | url=https://biblio.ugent.be/publication/434810 | hdl=1854/LU-434810 | s2cid=53518458 | hdl-access=free }}</ref> Bacteria in the microbial loop decompose this particulate detritus to utilize this energy-rich matter for growth. Since more than 95% of organic matter in marine ecosystems consists of polymeric, high [[molecular weight]] (HMW) compounds (e.g., protein, polysaccharides, lipids), only a small portion of total [[dissolved organic matter]] (DOM) is readily utilizable to most marine organisms at higher trophic levels. This means that dissolved organic carbon is not available directly to most marine organisms; [[marine bacteria]] introduce this organic carbon into the food web, resulting in additional energy becoming available to higher trophic levels.<ref name=Mentges2019>{{cite journal |doi = 10.1038/s41598-019-54290-z|title = Long-term stability of marine dissolved organic carbon emerges from a neutral network of compounds and microbes|year = 2019|last1 = Mentges|first1 = A.|last2 = Feenders|first2 = C.|last3 = Deutsch|first3 = C.|last4 = Blasius|first4 = B.|last5 = Dittmar|first5 = T.|journal = Scientific Reports|volume = 9|issue = 1|page = 17780|pmid = 31780725|pmc = 6883037|bibcode = 2019NatSR...917780M}}</ref>

{{clear}}

====Viral shunt====
{{multiple image
 | align = right
 | direction = horizontal
 | header    = Viral shunt
 | header_align      = 
 | width1    = 235
 | image1    = Viral shunt.jpg
 | caption1  = {{center| The viral shunt recycles DOM throughout the [[marine food web]]}}
 | width2    = 200
 | image2    = Structure of a Myoviridae bacteriophage 2.jpg
 | alt2      = 
 | caption2  =  {{center|Typical [[marine virus]]}}
}}
{{main|Viral shunt}}

As much as 25% of the primary production from phytoplankton in the global oceans may be recycled within the microbial loop through [[viral shunt]]ing.<ref>{{cite journal | last1 = Wilhelm | first1 = Steven W. | last2 = Suttle | first2 = Curtis A. | year = 1999 | title = Viruses and nutrient cycles in the sea: viruses play critical roles in the structure and function of aquatic food webs | journal = BioScience | volume = 49 | issue = 10| pages = 781–788 | doi = 10.2307/1313569 | jstor = 1313569 | doi-access = free}}</ref> The viral shunt  is a mechanism whereby [[marine viruses]] prevent  microbial [[particulate organic matter]] (POM) from migrating up [[trophic level]]s by recycling them into [[dissolved organic matter]] (DOM), which can be readily taken up by microorganisms. The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM.<ref>Robinson, Carol, and Nagappa Ramaiah. "Microbial heterotrophic metabolic rates constrain the microbial carbon pump." The American Association for the Advancement of Science, 2011.</ref> Viruses can easily infect microorganisms in the microbial loop due to their relative abundance compared to microbes.<ref name=":9">{{Cite journal|last=Fuhrman|first=Jed A.|date=1999|title=Marine viruses and their biogeochemical and ecological effects|journal=Nature|volume=399|issue=6736|pages=541–548|doi=10.1038/21119|pmid=10376593|issn=0028-0836|bibcode=1999Natur.399..541F|s2cid=1260399}}</ref><ref>{{Cite journal|last1=Wigington|first1=Charles H.|last2=Sonderegger|first2=Derek|last3=Brussaard|first3=Corina P. D.|last4=Buchan|first4=Alison|last5=Finke|first5=Jan F.|last6=Fuhrman|first6=Jed A.|last7=Lennon|first7=Jay T.|last8=Middelboe|first8=Mathias|last9=Suttle|first9=Curtis A.|last10=Stock|first10=Charles|last11=Wilson|first11=William H.|date=March 2016|title=Re-examination of the relationship between marine virus and microbial cell abundances|url=http://www.nature.com/articles/nmicrobiol201524|journal=Nature Microbiology|language=en|volume=1|issue=3|pages=15024|doi=10.1038/nmicrobiol.2015.24|pmid=27572161|s2cid=52829633|issn=2058-5276}}</ref> Prokaryotic and eukaryotic mortality contribute to carbon nutrient recycling through [[cell lysis]]. There is evidence as well of nitrogen (specifically ammonium) regeneration. This nutrient recycling helps stimulates microbial growth.<ref>Tsai, An-Yi, Gwo-Ching Gong, and Yu-Wen Huang. "Importance of the Viral Shunt in Nitrogen Cycling in Synechococcus Spp. Growth in Subtropical Western Pacific Coastal Waters." ''Terrestrial, Atmospheric & Oceanic Sciences''25.6 (2014).</ref>

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===Macroorganisms===

====Jelly fall====
[[File:Gelatinous zooplankton biological pump.png|thumb|upright=2| {{center|'''Gelatinous zooplankton biological pump'''}} How [[jelly carbon]] fits in the biological pump. A schematic representation of the biological pump and the biogeochemical processes that remove elements from the surface ocean by sinking biogenic particles including jelly carbon.<ref name=Lebrato2019>{{cite journal |title = Sinking of Gelatinous Zooplankton Biomass Increases Deep Carbon Transfer Efficiency Globally|year = 2019|doi = 10.1029/2019GB006265|last1 = Lebrato|first1 = Mario|last2 = Pahlow|first2 = Markus|last3 = Frost|first3 = Jessica R.|last4 = Küter|first4 = Marie|last5 = Jesus Mendes|first5 = Pedro|last6 = Molinero|first6 = Juan-Carlos|last7 = Oschlies|first7 = Andreas|journal = Global Biogeochemical Cycles|volume = 33|issue = 12|pages = 1764–1783|bibcode = 2019GBioC..33.1764L|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]
{{see also|Jelly falls}}

[[Jelly-falls]] are marine [[Carbon cycle|carbon cycling]] events whereby [[gelatinous zooplankton]], primarily [[cnidaria]]ns, sink to the seafloor and enhance carbon and nitrogen fluxes via rapidly sinking [[particulate organic matter]].<ref name="Lebrato et al. 2012">{{Cite journal |last1=Lebrato |first1=Mario |last2=Pitt |first2=Kylie A. |last3=Sweetman |first3=Andrew K. |last4=Jones |first4=Daniel O. B. |last5=Cartes |first5=Joan E. |last6=Oschlies |first6=Andreas |last7=Condon |first7=Robert H. |last8=Molinero |first8=Juan Carlos |last9=Adler |first9=Laetitia |name-list-style=amp |date=2012 |title=Jelly-falls historic and recent observations: a review to drive future research directions |journal=Hydrobiologia |volume=690 |issue=1 |pages=227–245 |doi=10.1007/s10750-012-1046-8|s2cid=15428213 |url=https://zenodo.org/record/3442888 }}</ref> These events provide nutrition to [[Benthic zone|benthic]] [[megafauna]] and [[bacteria]].<ref>{{Cite journal |last1=Lebrato |first1=M. |last2=Jones |first2=D. O. B. |name-list-style=amp |date=2009 |title=Mass deposition event of ''Pyrosoma atlanticum'' carcasses off Ivory Coast (West Africa) |journal=Limnology and Oceanography |volume=54 |issue=4 |pages=1197–1209 |doi=10.4319/lo.2009.54.4.1197|bibcode=2009LimOc..54.1197L |url=http://oceanrep.geomar.de/3017/1/1197.pdf |doi-access=free }}</ref><ref name="Sweetman and Chapman 2011">{{Cite journal |last1=Sweetman |first1=Andrew K. |last2=Chapman |first2=Annelise |name-list-style=amp |date=2011 |title=First observations of jelly-falls at the seafloor in a deep-sea fjord |journal=Deep Sea Research Part I: Oceanographic Research Papers |volume=58 |issue=12 |pages=1206–1211 |doi=10.1016/j.dsr.2011.08.006|bibcode=2011DSRI...58.1206S }}</ref> Jelly-falls have been implicated as a major "gelatinous pathway" for the [[Carbon sequestration|sequestration]] of [[Lability|labile]] biogenic carbon through the biological pump.<ref>{{cite web|last1=Burd|first1=Adrian|title=Towards a transformative understanding of the ocean's biological pump: Priorities for future research-Report on the NSF Biology of the Biological Pump Workshop.|url=http://www.us-ocb.org/publications/BioPump-Final.pdf|website=OCB: Ocean Carbon & Biogeochemistry|access-date=30 October 2016}}</ref> These events are common in protected areas with high levels of primary production and water quality suitable to support cnidarian species. These areas include [[Estuary|estuaries]] and several studies have been conducted in [[List of Norwegian fjords|fjords of Norway]].<ref name="Sweetman and Chapman 2011"/>

[[File:Jellyfish swarm.jpg|thumb|upright=1.3|left| Jellyfish are easy to capture and digest and may be more important as carbon sinks than was previously thought.<ref name=Hays2018>{{cite journal |doi = 10.1016/j.tree.2018.09.001|title = A Paradigm Shift in the Trophic Importance of Jellyfish?|year = 2018|last1 = Hays|first1 = Graeme C.|last2 = Doyle|first2 = Thomas K.|last3 = Houghton|first3 = Jonathan D.R.|journal = Trends in Ecology & Evolution|volume = 33|issue = 11|pages = 874–884|pmid = 30245075| bibcode=2018TEcoE..33..874H |s2cid = 52336522|url = https://pure.qub.ac.uk/en/publications/a-paradigm-shift-in-the-trophic-importance-of-jellyfish(6158fa15-32f8-4167-9574-dbc08266b588).html|author1-link = Graeme Hays}}</ref>]]

{{clear}}
 
====Whale pump====
{{see also|whale feces|whale fall}}

[[File:WhalePump.jpg|thumb|upright=2|right| The [[whale pump]] is the role played by whales and other marine mammals recycling nutrients in the ocean]]
[[Whale]]s and other [[marine mammal]]s also enhance primary productivity in their feeding areas by concentrating nitrogen near the surface through the release of [[flocculent]] [[fecal]] plumes.<ref name=Roman2013>{{cite journal |doi = 10.1371/journal.pone.0013255|title = The Whale Pump: Marine Mammals Enhance Primary Productivity in a Coastal Basin|year = 2010|last1 = Roman|first1 = Joe|last2 = McCarthy|first2 = James J.|journal = PLOS ONE|volume = 5|issue = 10|pages = e13255|pmid = 20949007|pmc = 2952594|bibcode = 2010PLoSO...513255R|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><ref name="ScienceDaily">{{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}}</ref> For example, whales and seals may be responsible for replenishing more nitrogen in the [[Gulf of Maine]]'s euphotic zone than the input of all rivers combined. This upward whale pump played a much larger role before industrial fishing devastated marine mammal stocks, when recycling of nitrogen was likely more than three times the atmospheric nitrogen input.<ref name=Roman2013 />

The biological pump mediates the removal of carbon and nitrogen from the euphotic zone through the downward flux of aggregates, feces, and vertical migration of invertebrates and fish.<ref>{{cite journal |doi = 10.1016/0079-6611(89)90010-4|title = The biological pump: Profiles of plankton production and consumption in the upper ocean|year = 1989|last1 = Longhurst|first1 = Alan R.|last2 = Glen Harrison|first2 = W.|journal = Progress in Oceanography|volume = 22|issue = 1|pages = 47–123|bibcode = 1989PrOce..22...47L}}</ref> Copepods and other zooplankton produce sinking fecal pellets and contribute to downward transport of dissolved and particulate organic matter by respiring and excreting at depth during migration cycles, thus playing an important role in the export of nutrients (N, P, and Fe) from surface waters.<ref>{{cite journal |doi = 10.4319/lo.1995.40.5.0989|title = Copepod grazing and the biogeochemical fate of diatom iron|year = 1995|last1 = Hutchins|first1 = David A.|last2 = Wang|first2 = Wen-Xiong|last3 = Fisher|first3 = Nicholas S.|journal = Limnology and Oceanography|volume = 40|issue = 5|pages = 989–994|bibcode = 1995LimOc..40..989H|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1016/S0967-0637(02)00037-7|title = Zooplankton vertical migration and the active transport of dissolved organic and inorganic nitrogen in the Sargasso Sea|year = 2002|last1 = Steinberg|first1 = Deborah K.|last2 = Goldthwait|first2 = Sarah A.|last3 = Hansell|first3 = Dennis A.|journal = Deep Sea Research Part I: Oceanographic Research Papers|volume = 49|issue = 8|pages = 1445–1461|bibcode = 2002DSRI...49.1445S}}</ref><ref name=Roman2013 />

Zooplankton feed in the euphotic zone and export nutrients via sinking fecal pellets, and vertical migration. Fish typically release nutrients at the same depth at which they feed. Excretion for marine mammals, tethered to the surface for respiration, is expected to be shallower in the water column than where they feed.<ref name=Roman2013 />

Marine mammals provide important ecosystem services. On a global scale, they can influence climate, through fertilization events and the export of carbon from surface waters to the deep sea through sinking whale carcasses.<ref>{{cite journal |doi = 10.1371/journal.pone.0012444|title = The Impact of Whaling on the Ocean Carbon Cycle: Why Bigger Was Better|year = 2010|last1 = Pershing|first1 = Andrew J.|last2 = Christensen|first2 = Line B.|last3 = Record|first3 = Nicholas R.|last4 = Sherwood|first4 = Graham D.|last5 = Stetson|first5 = Peter B.|journal = PLOS ONE|volume = 5|issue = 8|pages = e12444|pmid = 20865156|pmc = 2928761|bibcode = 2010PLoSO...512444P|doi-access = free}}</ref> In coastal areas, whales retain nutrients locally, increasing ecosystem productivity and perhaps raising the carrying capacity for other marine consumers, including commercial fish species.<ref name=Roman2013 /> It has been estimated that, in terms of carbon sequestration, one whale is equivalent to thousands of trees.<ref>{{cite web|url=https://www.imf.org/external/pubs/ft/fandd/2019/12/natures-solution-to-climate-change-chami.htm|title=Nature's Solution to Climate Change – IMF F&D|publisher=International Monetary Fund|access-date=2 November 2019}}</ref>

===Vertical migrations===
[[Diel vertical migration|Diel vertically migrating]] krill, salps, smaller zooplankton and fish can actively transport carbon to depth by consuming POC in the surface layer at night, and metabolising it at their daytime, mesopelagic residence depths. Depending on species life history, active transport may occur on a seasonal basis as well.<ref name=Cavan2019 />

Without vertical migration the biological pump  wouldn't be nearly as efficient. Organisms migrate up to feed at night so when they migrate back to depth during the day they defecate large sinking fecal pellets. Whilst some larger fecal pellets can sink quite fast, the speed that organisms move back to depth is still faster. At night organisms are in the top 100 metres of the water column, but during the day they move down to between 800 and 1000 metres. If organisms were to defecate at the surface it would take the fecal pellets days to reach the depth that they reach in a matter of hours. Therefore, by releasing fecal pellets at depth they have almost 1000 metres less to travel to get to the deep ocean. This is something known as [[active transport]]. The organisms are playing a more active role in moving organic matter down to depths. Because a large majority of the deep sea, especially marine microbes, depends on nutrients falling down, the quicker they can reach the ocean floor the better.<ref name=Steinberg2002 />

[[Zooplankton]] and [[salps]] play a large role in the active transport of fecal pellets. 15–50% of zooplankton biomass is estimated to migrate, accounting for the transport of 5–45% of particulate organic nitrogen to depth.<ref name=Steinberg2002 /> Salps are large gelatinous plankton that can vertically migrate 800 metres and eat large amounts of food at the surface. They have a very long gut retention time, so fecal pellets usually are released at maximum depth. Salps are also known for having some of the largest fecal pellets. Because of this they have a very fast sinking rate, small [[detritus]] particles are known to aggregate on them. This makes them sink that much faster. So while currently there is still much research being done on why organisms vertically migrate, it is clear that vertical migration plays a large role in the active transport of dissolved organic matter to depth.<ref name="Wiebe, P.H">{{cite journal | last=Wiebe | first=P.H |author2=L.P. Madin |author3=L.R. Haury |author4=G.R. Harbison |author5=L.M. Philbin |year=1979 | title=Diel Vertical Migration by Salpa aspera and its potential for large-scale particulate organic matter transport to the deep-sea | journal=Marine Biology | volume=53 | pages=249–255 | doi=10.1007/BF00952433 | issue=3| bibcode=1979MarBi..53..249W | s2cid=85127670 }}</ref>

====Lipid pump====
{{main|Lipid pump}}

The lipid pump sequesters [[carbon]] from the ocean's surface to deeper waters via [[lipid]]s associated with [[overwintering]] vertically migratory [[zooplankton]]. Lipids are a class of [[hydrocarbon]] rich, [[nitrogen]] and [[phosphorus]] deficient compounds essential for cellular structures. The lipid associated carbon enters the [[Deep sea|deep ocean]] as carbon dioxide produced by [[Respiration (physiology)|respiration]] of lipid reserves and as organic matter from the mortality of zooplankton. Compared to the more general biological pump, the lipid pump also results in a lipid shunt, where other [[nutrient]]s like nitrogen and phosphorus that are consumed in excess must be [[Excretion|excreted]] back to the surface environment, and thus are not removed from the surface mixed layer of the ocean.<ref name=":1">{{Cite journal|last1=Jónasdóttir|first1=Sigrún Huld|last2=Visser|first2=André W.|last3=Richardson|first3=Katherine|last4=Heath|first4=Michael R.|date=2015-09-29|title=Seasonal copepod lipid pump promotes carbon sequestration in the deep North Atlantic|journal=Proceedings of the National Academy of Sciences|language=en|volume=112|issue=39|pages=12122–12126|doi=10.1073/pnas.1512110112|issn=0027-8424|pmc=4593097|pmid=26338976|doi-access=free}}</ref> This means that the carbon transported by the lipid pump does not limit the availability of essential nutrients in the ocean surface. [[Carbon sequestration]] via the lipid pump is therefore decoupled from nutrient removal, allowing carbon uptake by oceanic primary production to continue. In the Biological Pump, nutrient removal is always coupled to carbon sequestration; primary production is limited as carbon and nutrients are transported to depth together in the form of organic matter.<ref name=":1" /> The contribution of the lipid pump to the sequestering of carbon in the deeper waters of the ocean can be substantial: the carbon transported below 1,000 metres (3,300&nbsp;ft) by [[copepod]]s of the genus ''[[Calanus]]'' in the [[Arctic Ocean]] almost equals that transported below the same depth annually by [[Particulate organic matter|particulate organic carbon]] (POC) in this region.<ref name=":2">{{Cite journal|last=Visser|first=Andre|date=2 March 2017|title=Calanus hyperboreus and the lipid pump|url=https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.10492|journal=Limnology and Oceanography|volume=62|issue=3|pages=1155–1165|doi=10.1002/lno.10492|bibcode=2017LimOc..62.1155V|s2cid=51989153 }}</ref> A significant fraction of this transported carbon would not return to the surface due to respiration and mortality. Research is ongoing to more precisely estimate the amount that remains at depth.<ref name=":1" /><ref name=":2" /><ref name=":3">{{Cite journal|last1=Steinberg|first1=Deborah K.|last2=Landry|first2=Michael R.|date=2017-01-03|title=Zooplankton and the Ocean Carbon Cycle|url=https://www.annualreviews.org/doi/10.1146/annurev-marine-010814-015924|journal=Annual Review of Marine Science|volume=9|issue=1|pages=413–444|doi=10.1146/annurev-marine-010814-015924|pmid=27814033|bibcode=2017ARMS....9..413S|issn=1941-1405}}</ref> The export rate of the lipid pump may vary from 1–9.3 g C m<sup>−2</sup> y<sup>−1</sup> across temperate and subpolar regions containing seasonally-migrating zooplankton.<ref name=":3" /> The role of zooplankton, and particularly copepods, in the [[food web]] is crucial to the survival of higher [[trophic level]] organisms whose primary source of [[nutrition]] is copepods. With warming oceans and increasing melting of [[ice cap]]s due to [[climate change]], the organisms associated with the lipid pump may be affected, thus influencing the survival of many commercially important [[fish]] and [[Endangered species|endangered]] [[marine mammal]]s.<ref>{{Cite journal|last1=Parent|first1=Genevieve J.|last2=Plourde|first2=Stephane|last3=Turgeon|first3=Julie|date=2011-11-01|title=Overlapping size ranges of Calanus spp. off the Canadian Arctic and Atlantic Coasts: impact on species' abundances|journal=Journal of Plankton Research|volume=33|issue=11|pages=1654–1665|doi=10.1093/plankt/fbr072|issn=0142-7873|doi-access=free}}</ref><ref>{{Cite journal|last1=Kristiansen|first1=Inga|last2=Gaard|first2=Eilif|last3=Hátún|first3=Hjálmar|last4=Jónasdóttir|first4=Sigrún|last5=Ferreira|first5=A. Sofia A.|date=2016-05-01|title=Persistent shift of Calanus spp. in the southwestern Norwegian Sea since 2003, linked to ocean climate|journal=ICES Journal of Marine Science|volume=73|issue=5|pages=1319–1329|doi=10.1093/icesjms/fsv222|issn=1054-3139|doi-access=free}}</ref><ref>{{Cite journal|last1=Jensen|first1=Maj Holst|last2=Nielsen|first2=Torkel Gissel|last3=Dahllöf|first3=Ingela|date=2008-04-28|title=Effects of pyrene on grazing and reproduction of Calanus finmarchicus and Calanus glacialis from Disko Bay, West Greenland|url=https://www.sciencedirect.com/science/article/pii/S0166445X08000179|journal=Aquatic Toxicology|language=en|volume=87|issue=2|pages=99–107|doi=10.1016/j.aquatox.2008.01.005|pmid=18291539|bibcode=2008AqTox..87...99J |issn=0166-445X}}</ref> As a new and previously unquantified component of oceanic carbon sequestration, further research on the lipid pump can improve the accuracy and overall understanding of carbon fluxes in [[Ocean|global oceanic systems]].<ref name=":1" /><ref name=":2" /><ref name=":3" />

===Bioluminescent shunt===
{{ see also|Bioluminescent bacteria|Particulate organic matter#Bioluminescent shunt hypothesis}}

[[File:Bioluminescence shunt in the marine carbon pump.png|thumb|upright=2| {{center|Bioluminescence shunt in the biological carbon pump in the ocean{{hsp}}<ref name=Tanet2020 />}}]]

[[Luminous bacteria]] in light organ symbioses are successively acquired by host (squid, fish) from the seawater while they are juveniles, then regularly released into the ocean.<ref name=Tanet2020>{{cite journal |doi = 10.5194/bg-17-3757-2020|title = Reviews and syntheses: Bacterial bioluminescence – ecology and impact in the biological carbon pump|year = 2020|last1 = Tanet|first1 = Lisa|last2 = Martini|first2 = Séverine|last3 = Casalot|first3 = Laurie|last4 = Tamburini|first4 = Christian|journal = Biogeosciences|volume = 17|issue = 14|pages = 3757–3778|bibcode = 2020BGeo...17.3757T|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

In the diagram on the right, depending on the light organ position, luminous bacteria are released from their guts into [[fecal pellet]]s or directly into the seawater (step 1). Motile luminous bacteria colonize organic matter sinking along the [[water column]]. Bioluminescent bacteria colonising fecal pellets and particles influence zooplankton consumption rates. Such visual markers increase detection ("bait hypothesis"), attraction and finally predation by upper [[trophic level]]s (step 2). In the [[mesopelagic]], zooplankton and their predators feed on sinking luminous particles and fecal pellets, which form either aggregates (repackaging) of faster sinking rates or fragment organic matter (due to sloppy feeding) with slower sinking rates (step 3).<ref name=Tanet2020 />

[[Filter feeder]]s also aggregate sinking organic matter without particular visual detection and selection of luminous matter. [[Diel vertical migration|Diel (and seasonal) vertical migrators]] feeding on luminous food metabolize and release glowing fecal pellets from the surface to the mesopelagic zone (step 4). This implies bioluminescent bacteria dispersion at large spatial scales, for zooplankton or even some fish actively swimming long distances. Luminous bacteria attached to particles sink down to the seafloor, and sediment can be resuspended by oceanographic physical conditions (step 5) and consumed by epi-benthic organisms. Instruments are (a) plankton net, (b) fish net, (c) [[Niskin bottle|Niskin water sampler]], (d) bathyphotometer, (e) [[sediment trap]]s, (f) [[autonomous underwater vehicle]]s, (g) [[photomultiplier]] module, (h) astrophysics optical modules [[ANTARES (telescope)|ANTARES]] and (i–j) [[remotely operated vehicle]]s.<ref name=Tanet2020 />

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==Quantification==
[[File:Global carbon stocks.png|thumb|upright=2|Diagram showing relative sizes (in gigatonnes) of the main storage pools of carbon on Earth. Cumulative changes (thru year 2014) from land use and emissions of fossil carbon are included for comparison.<ref name="janow">{{Cite book |url=https://www.fs.usda.gov/treesearch/pubs/54316 |title=Considering Forest and Grassland Carbon in Land Management |author=Kayler, Z., Janowiak, M., Swanston, C. |journal=General Technical Report WTO-GTR-95 |publisher=United States Department of Agriculture, Forest Service |chapter=The Global Carbon Cycle |pages=3–9 |year=2017|volume=95 |doi=10.2737/WO-GTR-95 }}</ref>]]
The geologic component of the carbon cycle operates slowly in comparison to the other parts of the global carbon cycle. It is one of the most important determinants of the amount of carbon in the atmosphere, and thus of global temperatures.<ref name=NASA>{{Cite web |title=The Slow Carbon Cycle |url=http://earthobservatory.nasa.gov/Features/CarbonCycle/page2.php |author=NASA |access-date=2012-06-24 |archive-url=https://web.archive.org/web/20120616151904/http://earthobservatory.nasa.gov/Features/CarbonCycle/page2.php |archive-date=16 June 2012 |url-status=live |df=dmy-all |date=2011-06-16 }}</ref>

As the biological pump plays an important role in the Earth's carbon cycle, significant effort is spent quantifying its strength.  However, because they occur as a result of poorly constrained ecological interactions usually at depth, the processes that form the biological pump are difficult to measure.  A common method is to estimate primary production fuelled by [[nitrate]] and [[ammonium]] as these nutrients have different sources that are related to the remineralisation of sinking material.  From these it is possible to derive the so-called [[f-ratio (oceanography)|f-ratio]], a proxy for the local strength of the biological pump.  Applying the results of local studies to the global scale is complicated by the role the ocean's circulation plays in different ocean regions.<ref name=marinov06>{{cite journal|last=Marinov|first=I. |author2=Gnanadesikan, A. |author3=Toggweiler, J. R. |author4=Sarmiento, J. L.|year=2006|title=The Southern Ocean biogeochemical divide|journal=Nature|volume=441|issue=7096|pages=964–967|doi=10.1038/nature04883|pmid=16791191|bibcode=2006Natur.441..964M |s2cid=4428683 }}</ref>

==Effects of climate change==
[[File:Temperature dependence of the biological pump.jpg|thumb|upright=2.0| {{center|'''Effect of temperature on the biological pump'''}} 
Effects of different water temperatures on organic carbon export and remineralization: more carbon is sequestered when temperature is colder compared to when is warmer.<ref name=Boscolo-Galazzo2018 />]]{{see also|Effects of climate change on oceans}}

Changes in land use, the [[combustion]] of [[fossil fuel]]s, and the production of [[cement]] have led to an increase in CO<sub>2</sub> concentration in the atmosphere.  At present, about one third (approximately 2 Pg C y<sup>−1</sup> = 2 × 10<sup>15</sup> grams of carbon per year)<ref name="tak02">{{cite journal|doi=10.1016/S0967-0645(02)00003-6    |title=Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects |year=2002 |last1=Takahashi |first1=Taro |last2=Sutherland |first2=Stewart C. |last3=Sweeney |first3=Colm |last4=Poisson |first4=Alain |last5=Metzl |first5=Nicolas |last6=Tilbrook |first6=Bronte |last7=Bates |first7=Nicolas |last8=Wanninkhof |first8=Rik |last9=Feely |first9=Richard A. |last10=Sabine |first10=Christopher |last11=Olafsson |first11=Jon |last12=Nojiri |first12=Yukihiro |journal=Deep Sea Research Part II: Topical Studies in Oceanography |volume=49 |issue=9–10 |pages=1601–1622 |bibcode=2002DSRII..49.1601T }}</ref><ref name="orr97">Orr, J. C., E. Maier-Reimer, U. Mikolajewicz, P. Monfray, J. L. Sarmiento, J. R. Toggweiler, N. K. Taylor, J. Palmer, N. Gruber, C. L. Sabine, C. Le Quéré, R. M. Key and J. Boutin (2001).  Estimates of anthropogenic carbon uptake from four three-dimensional global ocean models.  ''Global Biogeochem. Cycles'' '''15''', 43–60.</ref>{{Unreliable source?|date=May 2021|reason=rather old sources}} of anthropogenic emissions of CO<sub>2</sub> may be entering the ocean, but this is quite uncertain.<ref>{{Cite web|title=Study reveals uncertainty in how much carbon the ocean absorbs over time|url=https://news.mit.edu/2021/how-much-carbon-ocean-absorbs-0405|access-date=2021-05-07|website=MIT News {{!}} Massachusetts Institute of Technology|date=5 April 2021 |language=en}}</ref> Some research suggests that a link between elevated CO<sub>2</sub> and marine primary production exists.<ref>Riebesell, U., Schulz, K.G., Bellerby, R.G.J., Botros, M., Fritsche, P., Meyerhöfer, M., Neill, C., Nondal, G., Oschlies, A., Wohlers, J. and Zöllner, E. (2007).  [http://www.nature.com/nature/journal/v450/n7169/abs/nature06267.html Enhanced biological carbon consumption in a high CO<sub>2</sub> ocean.]  ''[[Nature (journal)|Nature]]'' '''450''', 545–548.</ref>

[[File:Arctic carbon fluxes influenced by sea ice decline and permafrost thaw.webp|thumb|upright=2.0| {{center|Arctic carbon fluxes influenced by sea ice decline<br />and permafrost thaw{{hsp}}<ref name=Parmentier2017>{{cite journal |doi = 10.1007/s13280-016-0872-8|title = A synthesis of the arctic terrestrial and marine carbon cycles under pressure from a dwindling cryosphere|year = 2017|last1 = Parmentier|first1 = Frans-Jan W.|last2 = Christensen|first2 = Torben R.|last3 = Rysgaard|first3 = Søren|last4 = Bendtsen|first4 = Jørgen|last5 = Glud|first5 = Ronnie N.|last6 = Else|first6 = Brent|last7 = Van Huissteden|first7 = Jacobus|last8 = Sachs|first8 = Torsten|last9 = Vonk|first9 = Jorien E.|last10 = Sejr|first10 = Mikael K.|journal = Ambio|volume = 46|issue = Suppl 1|pages = 53–69|pmid = 28116680|pmc = 5258664| bibcode=2017Ambio..46S..53P }} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><ref name=Parmentier2013>{{cite journal |doi = 10.1038/nclimate1784|title = The impact of lower sea-ice extent on Arctic greenhouse-gas exchange|year = 2013|last1 = Parmentier|first1 = Frans-Jan W.|last2 = Christensen|first2 = Torben R.|last3 = Sørensen|first3 = Lise Lotte|last4 = Rysgaard|first4 = Søren|last5 = McGuire|first5 = A. David|last6 = Miller|first6 = Paul A.|last7 = Walker|first7 = Donald A.|journal = Nature Climate Change|volume = 3|issue = 3|pages = 195–202|bibcode = 2013NatCC...3..195P}}</ref>}}]]

[[File:Vertically integrated anthropogenic dissolved inorganic carbon 1990s (GLODAP).png|thumb|upright=2.0| Global estimate of the vertically integrated anthropogenic [[dissolved inorganic carbon]] (DIC) in the ocean in recent times (1990s)]]

[[Climate change]] may affect the biological pump in the future by warming and [[Ocean stratification|stratifying]] the surface ocean.  It is believed that this could decrease the supply of nutrients to the euphotic zone, reducing primary production there.  Also, changes in the ecological success of [[Marine biogenic calcification|calcifying organisms]] caused by [[ocean acidification]] may affect the biological pump by altering the strength of the hard tissues pump.<ref name=orr05>{{Cite journal |last1=Orr |first1=James C. |last2=Fabry |first2=Victoria J. |last3=Aumont |first3=Olivier |last4=Bopp |first4=Laurent |last5=Doney |first5=Scott C. |last6=Feely |first6=Richard A. |last7=Gnanadesikan |first7=Anand |last8=Gruber |first8=Nicolas |last9=Ishida |first9=Akio |display-authors=etal |date=2005 |title=Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms |journal=Nature |volume=437 |issue=7059 |pages=681–686 |doi=10.1038/nature04095|pmid=16193043 |url=https://epic.awi.de/id/eprint/13479/1/Orr2005a.pdf |bibcode=2005Natur.437..681O |s2cid=4306199 }}</ref> This may then have a "knock-on" effect on the soft tissues pump because calcium carbonate acts to ballast sinking organic material.<ref>{{Cite journal |last1=Armstrong |first1=Robert A. |last2=Lee |first2=Cindy |last3=Hedges |first3=John I. |last4=Honjo |first4=Susumu |last5=Wakeham |first5=Stuart G. |name-list-style=amp|date=2001 |title=A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals |journal=Deep Sea Research Part II: Topical Studies in Oceanography |volume=49 |issue=1–3 |pages=219–236 |doi=10.1016/s0967-0645(01)00101-1|bibcode=2001DSRII..49..219A }}</ref>

The second diagram on the right shows some possible effects of sea ice decline and permafrost thaw on Arctic carbon fluxes. On land, plants take up carbon while microorganisms in the soil produce methane and respire CO<sub>2</sub>. Lakes are net emitters of methane, and organic and inorganic carbon (dissolved and particulate) flow into the ocean through freshwater systems. In the ocean, methane can be released from thawing subsea permafrost, and CO<sub>2</sub> is absorbed due to an undersaturation of CO<sub>2</sub> in the water compared with the atmosphere. In addition, multiple fluxes are closely associated to sea ice. Current best estimates of atmospheric fluxes are given in Tg C year<sup>−1</sup>, where available. Note that the emission estimate for lakes is for the area North of ~50º N rather than the narrower definition of arctic tundra for the other terrestrial fluxes. When available, uncertainty ranges are shown in brackets. The arrows do not represent the size of each flux.<ref name=Parmentier2013 /><ref name=Parmentier2017 />

The biological pump is thought to have played significant roles in atmospheric CO<sub>2</sub> fluctuations during past glacial-interglacial periods. However, it is not yet clear how the biological pump will respond to future climate change.<ref name=Turner2015 /> For such predictions to be reasonable, it is important to first decipher the response of phytoplankton, one of the key components of the biological pump to future changes in atmospheric CO<sub>2</sub>. Due to their phylogenetic diversity, different phytoplankton taxa will likely respond to climate change in different ways.<ref name=Collins2013 /> For instance, a decrease in the abundance of diatom is expected due to increased stratification in the future ocean.<ref>{{cite journal |doi = 10.1029/2005GL023653|title = Response of diatoms distribution to global warming and potential implications: A global model study|year = 2005|last1 = Bopp|first1 = L.|last2 = Aumont|first2 = O.|last3 = Cadule|first3 = P.|last4 = Alvain|first4 = S.|last5 = Gehlen|first5 = M.|journal = Geophysical Research Letters|volume = 32|issue = 19|pages = n/a|bibcode = 2005GeoRL..3219606B|doi-access = free}}</ref> Diatoms are highly efficient in transporting carbon to depths by forming large, rapidly sinking aggregates and their reduced numbers could in turn lead to decreased carbon export.<ref name=Passow2012 />

Further, decreased ocean pH due to ocean acidification may thwart the ability of coccolithophores to generate calcareous plates, potentially affecting the biological pump;<ref name=Collins2013 /> however, it appears that some species are more sensitive than others.<ref>{{cite journal |doi = 10.1126/science.1154122|title = Phytoplankton Calcification in a High-CO2 World|year = 2008|last1 = Iglesias-Rodriguez|first1 = M. D.|last2 = Halloran|first2 = P. R.|last3 = Rickaby|first3 = R. E. M.|last4 = Hall|first4 = I. R.|last5 = Colmenero-Hidalgo|first5 = E.|last6 = Gittins|first6 = J. R.|last7 = Green|first7 = D. R. H.|last8 = Tyrrell|first8 = T.|last9 = Gibbs|first9 = S. J.|last10 = von Dassow|first10 = P.|last11 = Rehm|first11 = E.|last12 = Armbrust|first12 = E. V.|last13 = Boessenkool|first13 = K. P.|journal = Science|volume = 320|issue = 5874|pages = 336–340|pmid = 18420926|bibcode = 2008Sci...320..336I|s2cid = 206511068}}</ref> Thus, future changes in the relative abundance of these or other phytoplankton taxa could have a marked impact on total ocean productivity, subsequently affecting ocean biogeochemistry and carbon storage. 

A 2015 study determined that [[coccolithophore]] concentrations in the North Atlantic have increased by an order of magnitude since the 1960s and an increase in absorbed CO<sub>2</sub>, as well as temperature, were modeled to be the most likely cause of this increase.<ref>{{Cite journal |last1=Rivero-Calle |first1=Sara |last2=Gnanadesikan |first2=Anand |last3=Castillo |first3=Carlos E. Del |last4=Balch |first4=William M. |last5=Guikema |first5=Seth D. |name-list-style=amp|date=2015 |title=Multidecadal increase in North Atlantic coccolithophores and the potential role of rising CO<sub>2</sub> |journal=Science |volume=350 |issue=6267 |pages=1533–1537 |doi=10.1126/science.aaa8026 |pmid=26612836|bibcode=2015Sci...350.1533R |doi-access=free }}</ref> 

In a 2017 study, scientists used [[species distribution modelling]] (SDM) to predict the future global distribution of two phytoplankton species important to the biological pump: the diatom ''[[Chaetoceros diadema]]'' and the coccolithophore ''[[Emiliania huxleyi]]''.<ref>{{cite journal |doi = 10.1111/maec.12427|title = Using species distribution modelling to predict future distributions of phytoplankton: Case study using species important for the biological pump|year = 2017|last1 = Jensen|first1 = Lasse Ørsted|last2 = Mousing|first2 = Erik Askov|last3 = Richardson|first3 = Katherine|journal = Marine Ecology|volume = 38|issue = 3|pages = e12427|bibcode = 2017MarEc..38E2427J}}</ref> They employed environmental data described in the [[IPCC]] [[Representative Concentration Pathways#RCP 8.5|Representative Concentration Pathways scenario 8.5]], which predicts [[radiative forcing]] in the year 2100 relative to pre-industrial values. Their modelling results predicted that the total ocean area covered by ''C. diadema'' and ''E. huxleyi'' would decline by 8% and 16%, respectively, under the examined climate scenario. They predicted changes in the range and distribution of these two phytoplankton species under these future ocean conditions, if realized, might result in reduced contribution to carbon sequestration via the biological pump.<ref name="Basu2018" />  In 2019, a study indicated that at current rates of seawater acidification, we could see Antarctic phytoplanktons smaller and less effective at storing carbon before the end of the century.<ref>{{Cite web|url=https://phys.org/news/2019-08-acid-oceans-plankton-fueling-faster.html|title=Acid oceans are shrinking plankton, fueling faster climate change|last1=Petrou|first1=Katherina|last2=Nielsen|first2=Daniel|date=2019-08-27|website=phys.org|language=en-us|access-date=2019-09-07}}</ref>

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==Monitoring==
[[File:Monitoring the ocean biological carbon pump.jpg|thumb|upright=2|{{center|'''Monitoring the ocean biological carbon pump'''{{hsp}}<ref name=Brewin2021 /> Pools, fluxes and processes that form the ocean biological carbon pump, and current methods used to monitor them. Bold black text and thick black arrows represent the key export pathways and interactions with other domains (land and atmosphere). Global stocks of the different carbon pools in the ocean are given in the box on the left; the four major kinds of pools – [[Dissolved inorganic carbon|DIC]], [[Dissolved organic carbon|DOC]], [[Particulate organic carbon|POC]] and [[Particulate inorganic carbon|PIC]] – are given in different colours.}}
{{center|<small>This figure has been inspired by, and builds on, two earlier figures, one from the [[CEOS]] carbon from space report{{hsp}}<ref>{{cite journal | last1=Siegel | first1=David A. | last2=Buesseler | first2=Ken O. | last3=Behrenfeld | first3=Michael J. | last4=Benitez-Nelson | first4=Claudia R. | last5=Boss | first5=Emmanuel | last6=Brzezinski | first6=Mark A. | last7=Burd | first7=Adrian | last8=Carlson | first8=Craig A. | last9=D'Asaro | first9=Eric A. | last10=Doney | first10=Scott C. | last11=Perry | first11=Mary J. | last12=Stanley | first12=Rachel H. R. | last13=Steinberg | first13=Deborah K. | title=Prediction of the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Science Plan | journal=Frontiers in Marine Science | publisher=Frontiers Media SA | volume=3 | date=2016-03-08 | issn=2296-7745 | doi=10.3389/fmars.2016.00022| doi-access=free }}</ref> and the other from the NASA EXPORTS plan.<ref>[[Committee on Earth Observation Satellites]] (2014) "CEOS strategy for carbon observations from space". Response to the [[Group on Earth Observations]] (GEO) carbon strategy. Printed in Japan by JAXA and I&A Corporation.</ref></small>}}]]
{{see also|Remote sensing (oceanography)}}

Monitoring the biological pump is critical to understanding how the Earth's carbon cycle is changing. A variety of techniques are used to monitor the biological pump, which can be deployed from various platforms such as ships, autonomous vehicles, and satellites. At present, satellite remote sensing is the only tool available for viewing the entire surface ocean at high temporal and spatial scales.<ref name=Brewin2021 />

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==Needed research==
[[File:Multidisciplinary observations in the water column needed to understand the biological pump.jpg|thumb|upright=2.0| {{center|Multidisciplinary observations still needed in the deep water column<br />to properly understand the biological pump{{hsp}}<ref name=Levin2019 />}} {{center|<small>EOVs {{=}} Essential Ocean Variables</small>}}]]

Multidisciplinary observations are still needed in the deep [[water column]] to properly understand the biological pump:<ref name=Levin2019>Levin, L.A., Bett, B.J., Gates, A.R., Heimbach, P., Howe, B.M., Janssen, F., McCurdy, A., Ruhl, H.A., Snelgrove, P., Stocks, K.I., Bailey, D. and 27 others (2019) "Global observing needs in the deep ocean". ''Frontiers in Marine Science'', '''6''': 241. {{doi|10.3389/fmars.2019.00241}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

* Physics: stratification affects particle sinking; understanding the origin of the particles and the residence time of the DIC from particle remineralization in the deep ocean requires measurement of advection and mixing.<ref name=Levin2019 />
* Biogeochemistry: export/mixing down of particulate and dissolved organic matter from the surface layer determines labile organic matter arriving at the seafloor, which is either respired by seafloor biota or stored for longer times in the sediment.<ref name=Levin2019 />
* Biology and ecosystems: zooplankton and microorganisms break down and remineralize sinking particles in the water column. Exported organic matter feeds all water column and benthic biota (zooplankton, benthic invertebrates, microbes) sustaining their biomass, density, and biodiversity.<ref name=Levin2019 />

==See also==
* [[f-ratio (oceanography)]]
* [[Lysocline]]
* [[Mooring (oceanography)]]
*[[Apparent oxygen utilisation]]

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==References==
{{reflist}}

{{microorganisms}}

{{DEFAULTSORT:Biological Pump}}
[[Category:Aquatic ecology]]
[[Category:Biological oceanography]]
[[Category:Carbon cycle]]
[[Category:Chemical oceanography]]