Editing Oxygen minimum zone (section)

=== Microbes ===
In OMZs oxygen concentration drops to levels <10 nM at the base of the oxycline and can remain anoxic for over 700 m depth.<ref name="Bertagnoli2018">{{cite journal |last1=Bertagnolli |first1=AD |last2=Stewart |first2=FJ |date=2018 |title=Microbial niches in marine oxygen minimum zones |journal=Nature Reviews Microbiology |volume=16 |issue=12 |pages=723–729 |doi=10.1038/s41579-018-0087-z |pmid=30250271 |s2cid=52811177}}</ref> This lack of oxygen can be reinforced or increased due to physical processes changing oxygen supply such as eddy-driven advection,<ref name="Bertagnoli2018" /> sluggish ventilation,<ref name="LK2011">{{cite journal |last1=Lam |first1=P |last2=Kuypers |first2=MM |date=2011 |title=Microbial nitrogen cycling processes in oxygen minimum zones |journal=Annual Review of Marine Science |volume=3 |pages=317–345 |bibcode=2011ARMS....3..317L |doi=10.1146/annurev-marine-120709-142814 |pmid=21329208 |hdl-access=free |hdl=21.11116/0000-0001-CA25-2}}</ref> increases in [[ocean stratification]], and increases in ocean temperature which reduces oxygen solubility.<ref name="Robinson2019">{{cite journal |last1=Robinson |first1=C |date=2019 |title=Microbial respiration, the engine of ocean deoxygenation |journal=Frontiers in Marine Science |volume=5 |page=533 |doi=10.3389/fmars.2018.00533 |s2cid=58010259 |doi-access=free}}</ref>

At a microscopic scale the processes causing ocean deoxygenation rely on microbial aerobic respiration.<ref name="Robinson2019" /> Aerobic respiration is a metabolic process that microorganisms like bacteria or archaea use to obtain energy by degrading organic matter, consuming oxygen, producing CO<sub>2</sub> and obtaining energy in the form of ATP.<ref name="Robinson2019" /> In the ocean surface photosynthetic microorganisms called phytoplankton use solar energy and CO<sub>2</sub> to build organic molecules (organic matter) releasing oxygen in the process.<ref name="SigmanHain2012">{{cite journal |last1=Sigman |first1=DM |last2=Hain |first2=MP |date=2012 |title=The biological productivity of the ocean |journal=Nature Education Knowledge |volume=3 |issue=6 |pages=1–16}}</ref>  A large fraction of the organic matter from photosynthesis becomes dissolved organic matter (DOM) that is consumed by bacteria during aerobic respiration in sunlit waters. Another fraction of organic matter sinks to the deep ocean forming aggregates called marine snow.<ref name="AzamMalfatti2007">{{cite journal |last1=Azam |first1=F |last2=Malfatti |first2=F |date=2007 |title=Microbial structuring of marine ecosystems |journal=Nature Reviews Microbiology |volume=5 |issue=10 |pages=782–791 |doi=10.1038/nrmicro1747 |pmid=17853906 |s2cid=10055219}}</ref> These sinking aggregates are consumed via degradation of organic matter and respiration at depth.<ref name="LK2011" />

At depths in the ocean where no light can reach, aerobic respiration is the dominant process. When the oxygen in a parcel of water is consumed, the oxygen cannot be replaced without the water reaching the surface ocean. When oxygen concentrations drop to below <10 nM, microbial processes that are normally inhibited by oxygen can take place like [[denitrification]] and [[anammox]]. Both processes extract elemental nitrogen from nitrogen compounds and that elemental nitrogen which does not stay in solution escapes as a gas, resulting in a net loss of nitrogen from the ocean.<ref name="LK2011" />