Editing Extinction event (section)

====Anoxic events====
[[Anoxic event]]s are situations in which the middle and even the upper layers of the ocean become deficient or totally lacking in oxygen. Their causes are complex and controversial, but all known instances are associated with severe and sustained global warming, mostly caused by sustained massive volcanism.<ref>{{cite journal |title = Geochemistry of oceanic anoxic events |journal = Geochemistry, Geophysics, Geosystems |date = 2010-03-01 |issn = 1525-2027 |pages = Q03004 |volume = 11|issue = 3|doi = 10.1029/2009GC002788 | vauthors = Jenkyns HC |bibcode=2010GGG....11.3004J|s2cid = 128598428 }}</ref>

It has been suggested that anoxic events caused or contributed to the [[Ordovician–Silurian extinction events|Ordovician–Silurian]],<ref name="QiuEtAl2022CommsEarthEnvironment">{{cite journal |last1=Qiu |first1=Zhen |last2=Zou |first2=Caineng |last3=Mills |first3=Benjamin J. W. |last4=Xiong |first4=Yijun |last5=Tao |first5=Huifei |last6=Lu |first6=Bin |last7=Liu |first7=Hanlin |last8=Xiao |first8=Wenjiao |last9=Poulton |first9=Simon W. |date=5 April 2022 |title=A nutrient control on expanded anoxia and global cooling during the Late Ordovician mass extinction |journal=[[Communications Earth & Environment]] |volume=3 |issue=1 |page=82 |doi=10.1038/s43247-022-00412-x |bibcode=2022ComEE...3...82Q |s2cid=247943064 |doi-access=free }}</ref><ref name=":12">{{Cite journal|last1=Zou|first1=Caineng|last2=Qiu|first2=Zhen|last3=Poulton|first3=Simon W.|last4=Dong|first4=Dazhong|last5=Wang|first5=Hongyan|last6=Chen|first6=Daizhou|last7=Lu|first7=Bin|last8=Shi|first8=Zhensheng|last9=Tao|first9=Huifei|date=2018|title=Ocean euxinia and climate change "double whammy" drove the Late Ordovician mass extinction|url=http://eprints.whiterose.ac.uk/129520/2/Revised%20Manuscript%20G40121.pdf|journal=[[Geology (journal)|Geology]]|volume=46|issue=6|pages=535–538|doi=10.1130/G40121.1|bibcode=2018Geo....46..535Z|s2cid=135039656 }}</ref><ref>{{cite journal |last1=Men |first1=Xin |last2=Mou |first2=Chuanlong |last3=Ge |first3=Xiangying |date=1 August 2022 |title=Changes in palaeoclimate and palaeoenvironment in the Upper Yangtze area (South China) during the Ordovician–Silurian transition |journal=[[Scientific Reports]] |volume=12 |issue=1 |page=13186 |doi=10.1038/s41598-022-17105-2 |pmid=35915216 |pmc=9343391 |bibcode=2022NatSR..1213186M }}</ref> [[Late Devonian extinction|late Devonian]],<ref>{{cite journal |last1=Bond |first1=David P. G. |last2=Zatoń |first2=Michał |last3=Wignall |first3=Paul B. |last4=Marynowski |first4=Leszek |date=11 March 2013 |title=Evidence for shallow-water 'Upper Kellwasser' anoxia in the Frasnian–Famennian reefs of Alberta, Canada |url=https://onlinelibrary.wiley.com/doi/full/10.1111/let.12014 |journal=[[Lethaia]] |volume=46 |issue=3 |pages=355–368 |doi=10.1111/let.12014 |bibcode=2013Letha..46..355B |access-date=12 January 2023|url-access=subscription }}</ref><ref name=Algeo1998>{{cite journal|author=Algeo, T.J.|year=1998|title=Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=353|issue=1365|pages=113–130|doi=10.1098/rstb.1998.0195|last2=Scheckler|first2=S. E.|pmc=1692181}}</ref><ref name=Bond2008>{{cite journal|doi=10.1016/j.palaeo.2008.02.015|title=The role of sea-level change and marine anoxia in the Frasnian-Famennian (Late Devonian) mass extinction|year=2008|author1=David P. G. Bond |author2=Paul B. Wignalla |volume=263|journal=  Palaeogeography, Palaeoclimatology, Palaeoecology|pages=107–118|issue=3–4|bibcode=2008PPP...263..107B|url=http://eprints.whiterose.ac.uk/3460/1/bondb2.pdf}}</ref> [[Capitanian mass extinction event|Capitanian]],<ref>{{cite journal |last1=Zhang |first1=Bolin |last2=Wignall |first2=Paul B. |last3=Yao |first3=Suping |last4=Hu |first4=Wenxuan |last5=Liu |first5=Biao |date=January 2021 |title=Collapsed upwelling and intensified euxinia in response to climate warming during the Capitanian (Middle Permian) mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X20302446 |journal=[[Gondwana Research]] |volume=89 |pages=31–46 |doi=10.1016/j.gr.2020.09.003 |bibcode=2021GondR..89...31Z |s2cid=224981591 |access-date=30 September 2022|url-access=subscription }}</ref><ref>{{cite journal |last1=Zhang |first1=Bolin |last2=Yao |first2=Suping |last3=Hu |first3=Wenxuan |last4=Ding |first4=Hai |last5=Liu |first5=Bao |last6=Ren |first6=Yongle |date=1 October 2019 |title=Development of a high-productivity and anoxic-euxinic condition during the late Guadalupian in the Lower Yangtze region: Implications for the mid-Capitanian extinction event |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821730977X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=531 |page=108630 |doi=10.1016/j.palaeo.2018.01.021 |bibcode=2019PPP...53108630Z |s2cid=133916878 |access-date=17 November 2022|url-access=subscription }}</ref><ref name="BondWignallGrasby2019">{{cite journal |last1=Bond |first1=David P. G. |last2=Wignall |first2=Paul B. |last3=Grasby |first3=Stephen E. |date=30 August 2019 |title=The Capitanian (Guadalupian, Middle Permian) mass extinction in NW Pangea (Borup Fiord, Arctic Canada): A global crisis driven by volcanism and anoxia |journal=[[Geological Society of America Bulletin]] |volume=132 |issue=5–6 |pages=931–942 |doi=10.1130/B35281.1 |s2cid=199104686 |doi-access=free }}</ref> [[Permian–Triassic extinction event|Permian–Triassic]],<ref name=Kump2005>{{cite journal|last=Kump|first=Lee |author2=Alexander Pavlov |author3=Michael A. Arthur|title=Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia|journal=Geology|year=2005|volume=33|issue=5 |pages=397–400|doi=10.1130/G21295.1|bibcode=2005Geo....33..397K}}</ref><ref>{{cite journal |last1=Hülse |first1=Dominik |last2=Lau |first2=Kimberly V. |last3=Van de Velde |first3=Sebastiaan J. |last4=Arndt |first4=Sandra |last5=Meyer |first5=Katja M. |last6=Ridgwell |first6=Andy |date=28 October 2021 |title=End-Permian marine extinction due to temperature-driven nutrient recycling and euxinia |url=https://www.nature.com/articles/s41561-021-00829-7?error=cookies_not_supported&code=65341cdd-dd3e-41c1-b577-b859ae06d053 |journal=[[Nature Geoscience]] |volume=14 |issue=11 |pages=862–867 |doi=10.1038/s41561-021-00829-7 |bibcode=2021NatGe..14..862H |hdl=2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/334194 |s2cid=240076553 |access-date=12 January 2023}}</ref><ref>{{cite journal |last1=Schobben |first1=Martin |last2=Foster |first2=William J. |last3=Sleveland |first3=Arve R. N. |last4=Zuchuat |first4=Valentin |last5=Svensen |first5=Henrik H. |last6=Planke |first6=Sverre |last7=Bond |first7=David P. G. |last8=Marcelis |first8=Fons |last9=Newton |first9=Robert J. |last10=Wignall |first10=Paul B. |last11=Poulton |first11=Simon W. |date=17 August 2020 |title=A nutrient control on marine anoxia during the end-Permian mass extinction |url=https://www.nature.com/articles/s41561-020-0622-1?error=cookies_not_supported&code=bd1d48f1-9898-484a-9c4d-3329db200edb |journal=[[Nature Geoscience]] |volume=13 |issue=9 |pages=640–646 |doi=10.1038/s41561-020-0622-1 |bibcode=2020NatGe..13..640S |hdl=1874/408736 |s2cid=221146234 |access-date=12 January 2023|hdl-access=free }}</ref> and [[Triassic–Jurassic extinction event|Triassic–Jurassic]] extinctions,<ref>{{cite journal |last1=Atkinson |first1=J. W. |last2=Wignall |first2=Paul B. |date=15 August 2019 |title=How quick was marine recovery after the end-Triassic mass extinction and what role did anoxia play? |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018219302330 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=528 |pages=99–119 |doi=10.1016/j.palaeo.2019.05.011 |bibcode=2019PPP...528...99A |s2cid=164911938 |access-date=20 December 2022}}</ref> as well as a number of lesser extinctions (such as the [[Ireviken event|Ireviken]], [[Lundgreni Event|Lundgreni]], [[Mulde event|Mulde]], [[Lau event|Lau]], [[Smithian-Spathian boundary extinction|Smithian-Spathian]], [[Toarcian turnover|Toarcian]], and [[Cenomanian-Turonian boundary event|Cenomanian–Turonian]] events). On the other hand, there are widespread black shale beds from the mid-Cretaceous that indicate anoxic events but are not associated with mass extinctions.

The [[bio-availability]] of [[Essential trace element|essential]] [[trace element]]s (in particular [[selenium]]) to potentially lethal lows has been shown to coincide with, and likely have contributed to, at least three mass extinction events in the oceans, that is, at the end of the Ordovician, during the Middle and Late Devonian, and at the end of the Triassic. During periods of low oxygen concentrations very soluble [[selenate]] (Se<sup>6+</sup>) is converted into much less soluble [[selenide]] (Se<sup>2-</sup>), elemental Se and organo-selenium complexes. Bio-availability of selenium during these extinction events dropped to about 1% of the current oceanic concentration, a level that has been proven lethal to many [[Extant taxon|extant]] organisms.<ref>{{cite journal | vauthors = Long JA, Large RR, Lee MS, Benton MJ, Danyushevsky LV, Chiappe LM, Halpin JA, Cantrill D, Lottermoser B |display-authors=6 |year=2015 |title=Severe selenium depletion in the Phanerozoic oceans as a factor in three global mass extinction events |journal= Gondwana Research |volume=36 |pages= 209–218 |doi=10.1016/j.gr.2015.10.001 |bibcode=2016GondR..36..209L |url=https://research-information.bristol.ac.uk/en/publications/severe-selenium-depletion-in-the-phanerozoic-oceans-as-a-factor-in-three-global-mass-extinction-events(68e97709-15fb-496b-b28d-f8ea9ea9b4fc).html |hdl=1983/68e97709-15fb-496b-b28d-f8ea9ea9b4fc|s2cid=129753283 |hdl-access=free }}</ref>

British [[oceanologist]] and [[atmospheric scientist]], [[Andrew Watson (scientist)|Andrew Watson]], explained that, while the [[Holocene|Holocene epoch]] exhibits many processes reminiscent of those that have contributed to past anoxic events, full-scale ocean anoxia would take "thousands of years to develop".<ref>{{cite journal | vauthors = Watson AJ | title = Oceans on the edge of anoxia | journal = Science | volume = 354 | issue = 6319 | pages = 1529–1530 | date = December 2016 | pmid = 28008026 | doi = 10.1126/science.aaj2321 | language = en | s2cid = 206653923 | bibcode = 2016Sci...354.1529W | hdl = 10871/25100 | hdl-access = free }}</ref>