Editing Ice sheet (section)

== Role in carbon cycle ==
[[File:Carbon stores and fluxes in present day ice sheets.webp|thumb|Carbon stores and fluxes in present-day ice sheets (2019), and the predicted impact on carbon dioxide (where data exists). <br /> Estimated carbon fluxes are measured in Tg C a<sup>−1</sup> (megatonnes of carbon per year) and estimated sizes of carbon stores are measured in Pg C (thousands of megatonnes of carbon). DOC = [[dissolved organic carbon]], POC = [[particulate organic carbon]].<ref name="Wadham2019" />]]

Historically, ice sheets were viewed as inert components of the [[Marine carbon cycle|carbon cycle]] and were largely disregarded in global models. In 2010s, research had demonstrated the existence of uniquely adapted [[Marine microorganisms|microbial communities]], high rates of [[Marine biogeochemical cycles|biogeochemical]] and physical weathering in ice sheets, and storage and cycling of organic carbon in excess of 100 billion tonnes.<ref name="Wadham2019" />

There is a massive contrast in carbon storage between the two ice sheets. While only about 0.5-27 billion tonnes of pure carbon are present underneath the Greenland ice sheet, 6000-21,000 billion tonnes of pure carbon are thought to be located underneath Antarctica.<ref name="Wadham2019">{{cite journal |last1=Wadham |first1=J. L. |last2=Hawkings |first2=J. R. |last3=Tarasov |first3=L. |last4=Gregoire |first4=L. J. |last5=Spencer |first5=R. G. M. |last6=Gutjahr |first6=M. |last7=Ridgwell |first7=A. |last8=Kohfeld |first8=K. E. |title=Ice sheets matter for the global carbon cycle |journal=Nature Communications |date=15 August 2019 |volume=10 |issue=1 |page=3567 |doi=10.1038/s41467-019-11394-4 |pmid=31417076 |pmc=6695407 |bibcode=2019NatCo..10.3567W |hdl=1983/19a3bd0c-eff6-48f5-a8b0-1908c2404a24 |hdl-access=free }}</ref> This carbon can act as a [[climate change feedback]] if it is gradually released through meltwater, thus increasing overall [[carbon dioxide emissions]].<ref>{{Cite journal |last1=Ryu |first1=Jong-Sik |last2=Jacobson |first2=Andrew D. |date=6 August 2012 |title=CO2 evasion from the Greenland Ice Sheet: A new carbon-climate feedback |journal=Chemical Geology |language=en |volume=320 |issue=13 |pages=80–95 |bibcode=2012ChGeo.320...80R |doi=10.1016/j.chemgeo.2012.05.024}}</ref>

For comparison, 1400–1650&nbsp;billion tonnes are contained within the Arctic [[permafrost]].<ref>{{cite journal |last1=Tarnocai, C. |author2=Canadell, J.G. |author3=Schuur, E.A.G. |author4=Kuhry, P. |author5=Mazhitova, G. |author6=Zimov, S. |date=June 2009 |title=Soil organic carbon pools in the northern circumpolar permafrost region |journal=Global Biogeochemical Cycles |volume=23 |issue=2 |page=GB2023 |bibcode=2009GBioC..23.2023T |doi=10.1029/2008gb003327 |doi-access=free}}</ref> Also for comparison, the annual human caused carbon dioxide emissions amount to around 40&nbsp;billion tonnes of {{CO2}}.<ref name="IPCC AR6 WG1 Ch.9" />{{rp|1237}}

In Greenland, there is one known area, at [[Russell Glacier (Greenland)|Russell Glacier]], where meltwater carbon is released into the atmosphere as [[methane]], which has a much larger [[global warming potential]] than carbon dioxide.<ref name="Christiansen2018">{{cite journal |last1=Christiansen |first1=Jesper Riis |last2=Jørgensen |first2=Christian Juncher |date=9 November 2018 |title=First observation of direct methane emission to the atmosphere from the subglacial domain of the Greenland Ice Sheet |journal=Scientific Reports |volume=8 |issue=1 |page=16623 |doi=10.1038/s41598-018-35054-7 |pmid=30413774 |pmc=6226494 |bibcode=2018NatSR...816623C }}</ref> However, it also harbours large numbers of [[methanotroph]]ic bacteria, which limit those emissions.<ref>{{cite journal |last1=Dieser |first1=Markus |last2=Broemsen |first2=Erik L J E |last3=Cameron |first3=Karen A |last4=King |first4=Gary M |last5=Achberger |first5=Amanda |last6=Choquette |first6=Kyla |last7=Hagedorn |first7=Birgit |last8=Sletten |first8=Ron |last9=Junge |first9=Karen |last10=Christner |first10=Brent C |date=17 April 2014 |title=Molecular and biogeochemical evidence for methane cycling beneath the western margin of the Greenland Ice Sheet |journal=The ISME Journal |volume=8 |issue=11 |pages=2305–2316 |doi=10.1038/ismej.2014.59 |pmid=24739624 |pmc=4992074 |bibcode=2014ISMEJ...8.2305D }}</ref><ref>{{cite journal |last1=Znamínko |first1=Matěj |last2=Falteisek |first2=Lukáš |last3=Vrbická |first3=Kristýna |last4=Klímová |first4=Petra |last5=Christiansen |first5=Jesper R. |last6=Jørgensen |first6=Christian J. |last7=Stibal |first7=Marek |title=Methylotrophic Communities Associated with a Greenland Ice Sheet Methane Release Hotspot |journal=Microbial Ecology |date=16 October 2023 |volume=86 |issue=4 |pages=3057–3067 |doi=10.1007/s00248-023-02302-x |pmid=37843656 |pmc=10640400 |bibcode=2023MicEc..86.3057Z }}</ref>