Editing Carbon cycle (section)

=== Biological pump in the ocean ===
[[File:Oceanic Food Web.jpg|thumb|upright=2| {{center|Flow of carbon through the open ocean}}]]
{{main|Biological pump}}

The ocean [[biological pump]] is the ocean's biologically driven sequestration of [[carbon]] from the atmosphere and land runoff to the deep ocean interior and [[seafloor sediments]].<ref name="Sigman DM 2006. pp. 491-528">{{cite book |doi=10.1016/B0-08-043751-6/06118-1 |bibcode=2003TrGeo...6..491S |chapter=The Biological Pump in the Past |title=Treatise on Geochemistry |date=2003 |last1=Sigman |first1=D.M. |last2=Haug |first2=G.H. |volume=6 |pages=491–528 |isbn=978-0-08-043751-4 }}</ref> 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. The pump transfers about 11 billion tonnes of carbon every year into the ocean's interior. An ocean without the biological pump would result in atmospheric CO<sub>2</sub> levels about 400 [[Parts per million|ppm]] higher than the present day.<ref>{{cite journal |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. |title=The Biological Carbon Pump in the North Atlantic |journal=Progress in Oceanography |date=December 2014 |volume=129 |pages=200–218 |doi=10.1016/j.pocean.2014.05.005 |bibcode=2014PrOce.129..200S }}</ref><ref>{{cite journal |last1=Boyd |first1=Philip W. |title=Toward quantifying the response of the oceans' biological pump to climate change |journal=Frontiers in Marine Science |date=13 October 2015 |volume=2 |doi=10.3389/fmars.2015.00077 |doi-access=free }}</ref><ref name=Basu2018>{{cite journal |last1=Basu |first1=Samarpita |last2=Mackey |first2=Katherine |title=Phytoplankton as Key Mediators of the Biological Carbon Pump: Their Responses to a Changing Climate |journal=Sustainability |date=19 March 2018 |volume=10 |issue=3 |pages=869 |doi=10.3390/su10030869 |doi-access=free }}</ref>

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 |last1=Steinberg |first1=Deborah K |last2=Goldthwait |first2=Sarah A |last3=Hansell |first3=Dennis A |title=Zooplankton vertical migration and the active transport of dissolved organic and inorganic nitrogen in the Sargasso Sea |journal=Deep Sea Research Part I: Oceanographic Research Papers |date=August 2002 |volume=49 |issue=8 |pages=1445–1461 |doi=10.1016/S0967-0637(02)00037-7 |bibcode=2002DSRI...49.1445S }}</ref>

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 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.<ref name=Ducklow2001 />

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 have sinking rates orders of magnitude greater than individual cells and complete their journey to the deep in a matter of days.<ref name=Rocha2006>{{cite book |last1=de la Rocha |first1=C.L. |chapter=The Biological Pump |pages=83–111 |chapter-url={{GBurl|BnZ77tb18UEC|p=83}} |editor1-last=Elderfield |editor1-first=H. |title=The Oceans and Marine Geochemistry |date=2006 |publisher=Elsevier |isbn=978-0-08-045101-5 }}</ref>

About 1% of the particles leaving the surface ocean reach the seabed and are consumed, respired, or buried in the sediments. 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 a surface-to-deep ocean gradient of DIC. [[Thermohaline circulation]] returns deep-ocean DIC to the atmosphere on millennial timescales. The carbon buried in the sediments can be [[subducted]] into the [[earth's mantle]] and stored for millions of years as part of the slow carbon cycle (see next section).<ref name=Ducklow2001>{{cite journal |last1=Ducklow |first1=Hugh |last2=Steinberg |first2=Deborah |last3=Buesseler |first3=Ken |title=Upper Ocean Carbon Export and the Biological Pump |journal=Oceanography |date=2001 |volume=14 |issue=4 |pages=50–58 |doi=10.5670/oceanog.2001.06 |doi-access=free }}{{Creative Commons text attribution notice|cc=by4|url=|author(s)=|vrt=|from this source=yes}}</ref>

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