Editing Permian–Triassic extinction event (section)

=== Anoxia and euxinia ===
{{See also|Anoxic event}}
Evidence for widespread ocean [[anoxic waters|anoxia]] (severe deficiency of oxygen) and [[euxinia]] (presence of [[hydrogen sulfide]]) is found from the Late Permian to the Early Triassic.<ref>{{cite journal |last1=Wang |first1=Han |last2=He |first2=Weihong |last3=Xiao |first3=Yifan |last4=Yang |first4=Tinglu |last5=Zhang |first5=Kexin |last6=Wu |first6=Huiting |last7=Huang |first7=Yafei |last8=Peng |first8=Xingfang |last9=Wu |first9=Shunbao |date=1 July 2023 |title=Stagewise collapse of biotic communities and its relations to oxygen depletion along the north margin of Nanpanjiang Basin during the Permian–Triassic transition |url=https://www.sciencedirect.com/science/article/pii/S0031018223001876 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=621 |page=111569 |doi=10.1016/j.palaeo.2023.111569 |bibcode=2023PPP...62111569W |access-date=31 May 2023|url-access=subscription }}</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=8 January 2023}}</ref><ref>{{Cite journal |last=Benton |first=Michael James |date=January 2008 |title=Presidential Address 2007: The end-Permian mass extinction — events on land in Russia |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787808803136 |journal=[[Proceedings of the Geologists' Association]] |language=en |volume=119 |issue=2 |pages=119–136 |doi=10.1016/S0016-7878(08)80313-6 |bibcode=2008PrGA..119..119B |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Throughout most of the [[Tethys Ocean|Tethys]] and [[Panthalassic]] Oceans, evidence for anoxia appears at the extinction event, including small pyrite [[framboid]]s,<ref name=WignallandTwitchett2002>{{cite book |last1=Wignall |first1=Paul Barry |last2=Twitchett |first2=Richard J. |editor-last1=Koeberl |editor-first1=Christian |editor-last2=MacLeod |editor-first2=Kenneth G. |date=2002 |title=Catastrophic Events and Mass Extinction: Impacts and Beyond |chapter=Extent, duration, and nature of the Permian-Triassic superanoxic event |chapter-url=https://www.researchgate.net/publication/279396802 |access-date=17 February 2024 |publisher=Geological Society of America Special Papers No. 356 |pages=395–413 |doi=10.1130/0-8137-2356-6.395 |isbn=9780813723563 |ol=11351081M |bibcode=2002GSASP.356..395W }}</ref><ref>{{Cite journal |last1=Wei |first1=Hengye |last2=Algeo |first2=Thomas J. |last3=Yu |first3=Hao |last4=Wang |first4=Jiangguo |last5=Guo |first5=Chuan |last6=Shi |first6=Guo |date=15 April 2015 |title=Episodic euxinia in the Changhsingian (late Permian) of South China: Evidence from framboidal pyrite and geochemical data |url=https://linkinghub.elsevier.com/retrieve/pii/S0037073815000494 |journal=Sedimentary Geology |language=en |volume=319 |pages=78–97 |doi=10.1016/j.sedgeo.2014.11.008 |bibcode=2015SedG..319...78W |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> negative δ<sup>238</sup>U excursions,<ref name="BrenneckaEtAl2011" /><ref>{{cite journal |last1=Wang |first1=Wen-qian |last2=Zhang |first2=Feifei |last3=Shen |first3=Shu-zhong |last4=Bizzarro |first4=Martin |last5=Garbelli |first5=Claudio |last6=Zheng |first6=Quan-feng |last7=Zhang |first7=Yi-chun |last8=Yuan |first8=Dong-xun |last9=Shi |first9=Yu-kun |last10=Cao |first10=Mengchun |last11=Dahl |first11=Tais W. |date=15 September 2022 |title=Constraining marine anoxia under the extremely oxygenated Permian atmosphere using uranium isotopes in calcitic brachiopods and marine carbonates |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X22003508 |journal=[[Earth and Planetary Science Letters]] |volume=594 |page=117714 |doi=10.1016/j.epsl.2022.117714 |bibcode=2022E&PSL.59417714W |s2cid=250941149 |access-date=31 May 2023|url-access=subscription }}</ref> negative δ<sup>15</sup>N excursions,<ref>{{cite journal |last1=Luo |first1=Genming |last2=Wang |first2=Yongbiao |last3=Algeo |first3=Thomas J. |last4=Kump |first4=Lee R. |last5=Bai |first5=Xiao |last6=Yang |first6=Hao |last7=Yao |first7=Le |last8=Xie |first8=Shucheng |date=1 July 2011 |title=Enhanced nitrogen fixation in the immediate aftermath of the latest Permian marine mass extinction |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/39/7/647/130602/Enhanced-nitrogen-fixation-in-the-immediate |journal=[[Geology (journal)|Geology]] |volume=39 |issue=7 |pages=647–650 |doi=10.1130/G32024.1 |bibcode=2011Geo....39..647L |access-date=26 May 2023|url-access=subscription }}</ref> positive δ<sup>82/78</sup>Se isotope excursions,<ref>{{Cite journal |last1=Stüeken |first1=Eva E. |last2=Foriel |first2=Julien |last3=Buick |first3=Roger |last4=Schoepfer |first4=Shane D. |date=2 September 2015 |title=Selenium isotope ratios, redox changes and biological productivity across the end-Permian mass extinction |url=https://linkinghub.elsevier.com/retrieve/pii/S0009254115002843 |journal=[[Chemical Geology]] |language=en |volume=410 |pages=28–39 |doi=10.1016/j.chemgeo.2015.05.021 |bibcode=2015ChGeo.410...28S |access-date=13 March 2024 |via=Elsevier Science Direct}}</ref> relatively positive δ<sup>13</sup>C ratios in polycyclic aromatic hydrocarbons,<ref>{{cite journal |last1=Grice |first1=Kliti |last2=Nabbefeld |first2=Birgit |last3=Maslen |first3=Ercin |date=November 2007 |title=Source and significance of selected polycyclic aromatic hydrocarbons in sediments (Hovea-3 well, Perth Basin, Western Australia) spanning the Permian–Triassic boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0146638007001581 |journal=[[Organic Geochemistry]] |volume=38 |issue=11 |pages=1795–1803 |doi=10.1016/j.orggeochem.2007.07.001 |bibcode=2007OrGeo..38.1795G |access-date=31 May 2023|url-access=subscription }}</ref> high Th/U ratios,<ref>{{cite journal |last1=Song |first1=Haijun |last2=Wignall |first2=Paul Barry |last3=Tong |first3=Jinnan |last4=Bond |first4=David P. G. |last5=Song |first5=Huyue |last6=Lai |first6=Xulong |last7=Zhang |first7=Kexin |last8=Wang |first8=Hongmei |last9=Chen |first9=Yanlong |date=1 November 2012 |title=Geochemical evidence from bio-apatite for multiple oceanic anoxic events during Permian–Triassic transition and the link with end-Permian extinction and recovery |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X12003640 |journal=[[Earth and Planetary Science Letters]] |volume=353-354 |pages=12–21 |bibcode=2012E&PSL.353...12S |doi=10.1016/j.epsl.2012.07.005 |access-date=13 January 2023|url-access=subscription }}</ref><ref name="BrenneckaEtAl2011">{{cite journal |last1=Brennecka |first1=Gregory A. |last2=Herrmann |first2=Achim D. |last3=Algeo |first3=Thomas J. |last4=Anbar |first4=Ariel D. |date=10 October 2011 |title=Rapid expansion of oceanic anoxia immediately before the end-Permian mass extinction |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=108 |issue=43 |pages=17631–17634 |doi=10.1073/pnas.1106039108 |pmid=21987794 |pmc=3203792 |doi-access=free }}</ref> positive Ce/Ce* anomalies,<ref>{{cite journal |last1=Müller |first1=J. |last2=Sun |first2=Y. D. |last3=Fang |first3=F. |last4=Regulous |first4=M. |last5=Joachimski |first5=Michael M. |date=March 2023 |title=Manganous water column in the Tethys Ocean during the Permian-Triassic transition |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818123000401 |journal=[[Global and Planetary Change]] |volume=222 |page=104067 |doi=10.1016/j.gloplacha.2023.104067 |bibcode=2023GPC...22204067M |s2cid=256800036 |access-date=26 June 2023|url-access=subscription }}</ref> depletions of molybdenum, uranium, and vanadium from seawater,<ref>{{Cite journal |last1=Xiang |first1=Lei |last2=Zhang |first2=Hua |last3=Schoepfer |first3=Shane D. |last4=Cao |first4=Chang-qun |last5=Zheng |first5=Quan-feng |last6=Yuan |first6=Dong-xun |last7=Cai |first7=Yao-feng |last8=Shen |first8=Shu-zhong |date=15 April 2020 |title=Oceanic redox evolution around the end-Permian mass extinction at Meishan, South China |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018219306078 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=544 |pages=109626 |doi=10.1016/j.palaeo.2020.109626 |bibcode=2020PPP...54409626X |access-date=1 August 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> and fine laminations in sediments.<ref name=WignallandTwitchett2002 /> However, evidence for anoxia precedes the extinction at some other sites, including [[Spiti]], [[India]],<ref>{{cite journal |last1=Stebbins |first1=Alan |last2=Williams |first2=Jeremy |last3=Brookfield |first3=Michael |last4=Nye Jr. |first4=Steven W. |last5=Hannigan |first5=Robyn |date=15 February 2019 |title=Frequent euxinia in southern Neo-Tethys Ocean prior to the end-Permian biocrisis: Evidence from the Spiti region, India |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=516 |pages=1–10 |doi=10.1016/j.palaeo.2018.11.030 |bibcode=2019PPP...516....1S |s2cid=134724104 |doi-access=free }}</ref> Shangsi, China,<ref>{{cite journal |last1=Zhang |first1=Li-Jun |last2=Zhang |first2=Xin |last3=Buatois |first3=Luis A. |last4=Mángano |first4=M. Gabriela |last5=Shi |first5=Guang R. Shi |last6=Gong |first6=Yi-Ming |last7=Qi |first7=Yong-An |date=December 2000 |title=Periodic fluctuations of marine oxygen content during the latest Permian |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818120302174 |journal=[[Global and Planetary Change]] |volume=195 |page=103326 |doi=10.1016/j.gloplacha.2020.103326 |s2cid=224881713 |access-date=2 March 2023|url-access=subscription }}</ref> [[Meishan]], China,<ref name=Caoetal2009>{{cite journal |last=Cao |first=Changqun |author2=Gordon D. Love |author3=Lindsay E. Hays |author4=Wei Wang |author5=Shuzhong Shen |author6=Roger E. Summons |title=Biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end-Permian mass extinction event |journal=[[Earth and Planetary Science Letters]] |year=2009 |volume=281 |issue=3–4 |pages=188–201 |doi=10.1016/j.epsl.2009.02.012 |bibcode=2009E&PSL.281..188C
}}</ref> Opal Creek, [[Alberta]],<ref>{{cite journal |last1=Schoepfer |first1=Shane D. |last2=Henderson |first2=Charles M. |last3=Garrison |first3=Geoffrey H. |last4=Ward |first4=Peter Douglas |date=1 January 2012 |title=Cessation of a productive coastal upwelling system in the Panthalassic Ocean at the Permian–Triassic Boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018211005281 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=313-314 |pages=181–188 |doi=10.1016/j.palaeo.2011.10.019 |bibcode=2012PPP...313..181S |access-date=21 December 2022|url-access=subscription }}</ref> and Kap Stosch, Greenland.<ref name=Hays2012>{{cite journal|last=Hays|first=Lindsay|author2=Kliti Grice |author3=Clinton B. Foster |author4=Roger E. Summons |title=Biomarker and isotopic trends in a Permian–Triassic sedimentary section at Kap Stosch, Greenland|journal=[[Organic Geochemistry]]|year=2012|volume=43|pages=67–82|doi=10.1016/j.orggeochem.2011.10.010|bibcode=2012OrGeo..43...67H |url=https://espace.curtin.edu.au/bitstream/20.500.11937/26597/2/170581_StreamGate.pdf|hdl=20.500.11937/26597|hdl-access=free}}</ref> Biogeochemical evidence also points to the presence of euxinia during the PTME.<ref>{{cite journal |last1=Hays |first1=Lindsay E. |last2=Beatty |first2=Tyler |last3=Henderson |first3=Charles M. |last4=Love |first4=Gordon D. |last5=Summons |first5=Roger E. |date=January–September 2007 |title=Evidence for photic zone euxinia through the end-Permian mass extinction in the Panthalassic Ocean (Peace River Basin, Western Canada) |url=https://www.sciencedirect.com/science/article/abs/pii/S1871174X07000169 |journal=[[Palaeoworld]] |volume=16 |issue=1–3 |pages=39–50 |doi=10.1016/j.palwor.2007.05.008 |access-date=23 May 2023|url-access=subscription }}</ref> Biomarkers for green sulfur bacteria, such as isorenieratane, the [[Diagenesis|diagenetic]] product of [[isorenieratene]], are widely used as indicators of [[photic zone]] euxinia because green sulfur [[bacteria]] require both sunlight and hydrogen sulfide to survive. Their abundance in sediments from the P–T boundary indicates euxinic conditions were present even in the shallow waters of the photic zone.<ref>{{cite journal |last1=Xie |first1=Shucheng |last2=Algeo |first2=Thomas J. |last3=Zhou |first3=Wenfeng |last4=Ruan |first4=Xiaoyan |last5=Luo |first5=Genming |last6=Huang |first6=Junhua |last7=Yan |first7=Jiaxin |date=15 February 2017 |title=Contrasting microbial community changes during mass extinctions at the Middle/Late Permian and Permian/Triassic boundaries |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X16307282 |journal=[[Earth and Planetary Science Letters]] |volume=460 |pages=180–191 |doi=10.1016/j.epsl.2016.12.015 |bibcode=2017E&PSL.460..180X |access-date=4 January 2023|url-access=subscription }}</ref><ref>{{Cite journal |last1=Luo |first1=Genming |last2=Huang |first2=Junhuang |last3=Xie |first3=Shucheng |last4=Wignall |first4=Paul Barry |last5=Tang |first5=Xinyan |last6=Huang |first6=Xianyu |last7=Yin |first7=Hongfu |date=13 February 2009 |title=Relationships between carbon isotope evolution and variation of microbes during the Permian–Triassic transition at Meishan Section, South China |url=http://link.springer.com/10.1007/s00531-009-0421-9 |journal=[[International Journal of Earth Sciences]] |language=en |volume=99 |issue=4 |pages=775–784 |doi=10.1007/s00531-009-0421-9 |issn=1437-3254 |access-date=1 August 2024 |via=Springer Link|url-access=subscription }}</ref> Negative mercury isotope excursions further bolster evidence for extensive euxinia during the PTME.<ref>{{cite journal |last1=Sun |first1=Ruoyu |last2=Liu |first2=Yi |last3=Sonke |first3=Jeroen E. |last4=Feifei |first4=Zhang |last5=Zhao |first5=Yaqiu |last6=Zhang |first6=Yonggen |last7=Chen |first7=Jiubin |last8=Liu |first8=Cong-Qiang |last9=Shen |first9=Shuzhong |last10=Anbar |first10=Ariel D. |last11=Zheng |first11=Wang |date=8 May 2023 |title=Mercury isotope evidence for marine photic zone euxinia across the end-Permian mass extinction |journal=[[Communications Earth & Environment]] |volume=4 |issue=1 |page=159 |doi=10.1038/s43247-023-00821-6 |bibcode=2023ComEE...4..159S |s2cid=258577845 |doi-access=free }}</ref> The disproportionate extinction of high-latitude marine species provides further evidence for oxygen depletion as a killing mechanism; low-latitude species living in warmer, less oxygenated waters are naturally better adapted to lower levels of oxygen and are able to migrate to higher latitudes during periods of global warming, whereas high-latitude organisms are unable to escape from warming, hypoxic waters at the poles.<ref name="PennDeutschPayneSperling2018">{{cite journal |last1=Penn |first1=Justin L. |last2=Deutsch |first2=Curtis |last3=Payne |first3=Jonathan L. |last4=Sperling |first4=Erik A. |date=7 December 2018 |title=Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction |journal=[[Science (journal)|Science]] |volume=362 |issue=6419 |pages=1–6 |doi=10.1126/science.aat1327 |pmid=30523082 |bibcode=2018Sci...362.1327P |s2cid=54456989 |doi-access=free }}</ref> Evidence of a lag between volcanic mercury inputs and biotic turnovers provides further support for anoxia and euxinia as the key killing mechanism, because extinctions would be expected to be synchronous with volcanic mercury discharge if volcanism and hypercapnia was the primary driver of extinction.<ref>{{cite journal |last1=Shen |first1=Jun |last2=Chen |first2=Jiubin |last3=Algeo |first3=Thomas J. |last4=Yuan |first4=Shengliu |last5=Feng |first5=Qinglai |last6=Yu |first6=Jianxin |last7=Zhou |first7=Lian |last8=O'Connell |first8=Brennan |last9=Planavsky |first9=Noah J. |date=5 April 2019 |title=Evidence for a prolonged Permian–Triassic extinction interval from global marine mercury records |journal=[[Nature Communications]] |volume=10 |issue=1 |page=1563 |doi=10.1038/s41467-019-09620-0 |pmid=30952859 |pmc=6450928 |bibcode=2019NatCo..10.1563S }}</ref> The sequence of extinctions in some sections, with deep water organisms being affected first followed by shallow water and then by bottom water organisms, is believed to reflect the migration of oxygen minimum zones.<ref>{{Cite journal |last1=He |first1=Weihong |last2=Weldon |first2=Elizabeth A. |last3=Yang |first3=Tinglu |last4=Wang |first4=Han |last5=Xiao |first5=Yifan |last6=Zhang |first6=Kexin |last7=Peng |first7=Xingfang |last8=Feng |first8=Qinglai |date=1 September 2024 |title=An end-Permian two-stage extinction pattern in the deep-water Dongpan Section, and its relationship to the migration and vertical expansion of the oxygen minimum zone in the South China Basin |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018224002967 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=649 |pages=112307 |doi=10.1016/j.palaeo.2024.112307 |bibcode=2024PPP...64912307H |access-date=13 October 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Models of [[ocean chemistry]] suggest that anoxia and euxinia were closely associated with [[hypercapnia]]. This suggests that poisoning from [[hydrogen sulfide]], anoxia, and hypercapnia acted together as a killing mechanism. Hypercapnia best explains the selectivity of the extinction, but anoxia and euxinia probably contributed to the high mortality of the event.<ref name="Meyers2008">{{cite journal |last=Meyers |first=Katja |author2=L.R. Kump |author3=A. Ridgwell |date=September 2008 |title=Biogeochemical controls on photic-zone euxinia during the end-Permian mass extinction |journal=[[Geology (journal)|Geology]] |volume=36 |issue=9 |pages=747–750 |bibcode=2008Geo....36..747M |doi=10.1130/g24618a.1}}</ref>

The sequence of events leading to anoxic oceans may have been triggered by carbon dioxide emissions from the eruption of the Siberian Traps.<ref name="EPMEPETM" /> In that scenario, warming from the enhanced greenhouse effect would reduce the solubility of oxygen in seawater, causing the concentration of oxygen to decline. Increased coastal evaporation would have caused the formation of warm saline bottom water (WSBW) depleted in oxygen and nutrients, which spread across the world through the deep oceans. The influx of WSBW caused thermal expansion of water that raised sea levels, bringing anoxic waters onto shallow shelfs and enhancing the formation of WSBW in a positive feedback loop.<ref>{{cite journal |last1=Kidder |first1=David L. |last2=Worsley |first2=Thomas R. |date=15 February 2004 |title=Causes and consequences of extreme Permo-Triassic warming to globally equable climate and relation to the Permo-Triassic extinction and recovery |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018203006679 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=203 |issue=3–4 |pages=207–237 |doi=10.1016/S0031-0182(03)00667-9 |bibcode=2004PPP...203..207K |access-date=23 May 2023|url-access=subscription }}</ref> The flux of terrigeneous material into the oceans increased as a result of soil erosion, which would have facilitated increased eutrophication;<ref>{{cite journal |last1=Sephton |first1=Mark A. |last2=Looy |first2=Cindy V. |last3=Brinkhuis |first3=Henk |last4=Wignall |first4=Paul Barry |last5=De Leeuw |first5=Jan W. |last6=Visscher |first6=Henk |date=1 December 2005 |title=Catastrophic soil erosion during the end-Permian biotic crisis |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/33/12/941/129272/Catastrophic-soil-erosion-during-the-end-Permian?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=33 |issue=12 |pages=941–944 |doi=10.1130/G21784.1 |bibcode=2005Geo....33..941S |access-date=26 May 2023|url-access=subscription }}</ref> marine regression likewise enhanced terrigeneous material inputs.<ref>{{Cite journal |last1=Duan |first1=Xiong |last2=Shi |first2=Zhiqiang |date=30 May 2024 |title=Sedimentary records of sea level fall during the end-Permian in the upper Yangtze region (southern China): Implications for the mass extinction |journal=[[Heliyon]] |language=en |volume=10 |issue=10 |pages=e31226 |doi=10.1016/j.heliyon.2024.e31226 |doi-access=free |pmc=11126861 |pmid=38799747 |bibcode=2024Heliy..1031226D }}</ref> Increased chemical weathering of the continents due to warming and the acceleration of the [[water cycle]] would increase the riverine flux of nutrients to the ocean.<ref>{{cite journal |last1=Algeo |first1=Thomas J. |last2=Henderson |first2=Charles M. |last3=Tong |first3=Jinnan |last4=Feng |first4=Qinglai |last5=Yin |first5=Hongfu |last6=Tyson |first6=Richard V. |date=June 2013 |title=Plankton and productivity during the Permian–Triassic boundary crisis: An analysis of organic carbon fluxes |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818112000380 |journal=[[Global and Planetary Change]] |volume=105 |pages=52–67 |doi=10.1016/j.gloplacha.2012.02.008 |bibcode=2013GPC...105...52A |access-date=3 July 2023|url-access=subscription }}</ref> Additionally, the Siberian Traps directly fertilised the oceans with iron and phosphorus as well, triggering bioblooms and marine snowstorms. Increased [[phosphate]] levels would have supported greater primary productivity in the surface oceans.<ref>{{Cite journal |last1=Grasby |first1=Stephen E. |last2=Ardakani |first2=Omid H. |last3=Liu |first3=Xiaojun |last4=Bond |first4=David P. G. |last5=Wignall |first5=Paul Barry |last6=Strachan |first6=Lorna J. |date=29 November 2023 |title=Marine snowstorm during the Permian−Triassic mass extinction |journal=[[Geology (journal)|Geology]] |volume=52 |issue=2 |pages=120–124 |language=en |doi=10.1130/G51497.1 |issn=0091-7613 |doi-access=free }}</ref> The increase in organic matter production would have caused more organic matter to sink into the deep ocean, where its respiration would further decrease oxygen concentrations. Once anoxia became established, it would have been sustained by a [[Positive feedback|positive feedback loop]] because deep water anoxia tends to increase the recycling efficiency of phosphate, leading to even higher productivity.<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 Barry |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=8 January 2023|hdl-access=free }}</ref> Along the Panthalassan coast of South China, oxygen decline was also driven by large-scale upwelling of deep water enriched in various nutrients, causing this region of the ocean to be hit by especially severe anoxia.<ref>{{cite journal |last1=Liao |first1=Wei |last2=Bond |first2=David P. G. |last3=Wang |first3=Yongbiao |last4=He |first4=Lei |last5=Yang |first5=Hao |last6=Weng |first6=Zeting |last7=Li |first7=Guoshan |date=15 November 2017 |title=An extensive anoxic event in the Triassic of the South China Block: A pyrite framboid study from Dajiang and its implications for the cause(s) of oxygen depletion |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821630699X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=486 |pages=86–95 |doi=10.1016/j.palaeo.2016.11.012 |bibcode=2017PPP...486...86L |access-date=8 May 2023}}</ref> Convective overturn helped facilitate the expansion of anoxia throughout the water column.<ref>{{cite journal |last1=Fio |first1=Karmen |last2=Spangenberg |first2=Jorge E. |last3=Vlahović |first3=Igor |last4=Sremac |first4=Jasenka |last5=Velić |first5=Ivo |last6=Mrinjek |first6=Ervin |date=1 November 2010 |title=Stable isotope and trace element stratigraphy across the Permian–Triassic transition: A redefinition of the boundary in the Velebit Mountain, Croatia |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254110003013 |journal=[[Chemical Geology]] |volume=278 |issue=1–2 |pages=38–57 |doi=10.1016/j.chemgeo.2010.09.001 |bibcode=2010ChGeo.278...38F |access-date=24 April 2023|url-access=subscription }}</ref> A severe [[anoxic event]] at the end of the Permian would have allowed [[sulfate-reducing bacteria]] to thrive, causing the production of large amounts of hydrogen sulfide in the anoxic ocean, turning it euxinic.<ref name="EPMEPETM">{{cite journal |last1=Saunders |first1=Andrew D. |date=9 June 2015 |title=Two LIPs and two Earth-system crises: the impact of the North Atlantic Igneous Province and the Siberian Traps on the Earth-surface carbon cycle |url=https://pubs.geoscienceworld.org/geolmag/article-abstract/153/2/201/251172/Two-LIPs-and-two-Earth-system-crises-the-impact-of?redirectedFrom=fulltext |journal=[[Geological Magazine]] |volume=153 |issue=2 |pages=201–222 |doi=10.1017/S0016756815000175 |s2cid=131273374 |access-date=26 May 2023|hdl=2381/32095 |hdl-access=free }}</ref> In some regions, anoxia briefly disappeared when transient cold snaps resulting from volcanic sulphur emissions occurred.<ref>{{Cite journal |last1=Newby |first1=Sean M. |last2=Owens |first2=Jeremy D. |last3=Schoepfer |first3=Shane D. |last4=Algeo |first4=Thomas J. |date=2 August 2021 |title=Transient ocean oxygenation at end-Permian mass extinction onset shown by thallium isotopes |url=https://www.nature.com/articles/s41561-021-00802-4 |journal=[[Nature Geoscience]] |language=en |volume=14 |issue=9 |pages=678–683 |doi=10.1038/s41561-021-00802-4 |bibcode=2021NatGe..14..678N |s2cid=236780878 |issn=1752-0908 |access-date=27 December 2023|url-access=subscription }}</ref>

The persistence of anoxia through the Early Triassic may explain the slow recovery of marine life and low levels of biodiversity after the extinction,<ref>{{cite journal |last1=Shen |first1=Jun |last2=Schoepfer |first2=Shane D. |last3=Feng |first3=Qinglai |last4=Zhou |first4=Lian |last5=Yu |first5=Jianxin |last6=Song |first6=Huyue |last7=Wei |first7=Hengye |last8=Algeo |first8=Thomas J. |date=October 2015 |title=Marine productivity changes during the end-Permian crisis and Early Triassic recovery |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825214001925 |journal=[[Earth-Science Reviews]] |volume=149 |pages=136–162 |doi=10.1016/j.earscirev.2014.11.002 |bibcode=2015ESRv..149..136S |access-date=20 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Wignall |first1=Paul Barry |last2=Hallam |first2=Anthony |date=May 1992 |title=Anoxia as a cause of the Permian/Triassic mass extinction: facies evidence from northern Italy and the western United States |url=https://www.sciencedirect.com/science/article/abs/pii/0031018292901825 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=93 |issue=1–2 |pages=21–46 |doi=10.1016/0031-0182(92)90182-5 |bibcode=1992PPP....93...21W |access-date=20 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Chen |first1=Zhong-Qiang |last2=Yang |first2=Hao |last3=Luo |first3=Mao |last4=Benton |first4=Michael James |last5=Kaiho |first5=Kunio |last6=Zhao |first6=Laishi |last7=Huang |first7=Yuangeng |last8=Zhang |first8=Kexing |last9=Fang |first9=Yuheng |last10=Jiang |first10=Haishui |last11=Qiu |first11=Huan |last12=Li |first12=Yang |last13=Tu |first13=Chengyi |last14=Shi |first14=Lei |last15=Zhang |first15=Lei |last16=Feng |first16=Xueqian |last17=Chen |first17=Long |date=October 2015 |title=Complete biotic and sedimentary records of the Permian–Triassic transition from Meishan section, South China: Ecologically assessing mass extinction and its aftermath |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825214001846 |journal=[[Earth-Science Reviews]] |volume=149 |pages=67–107 |doi=10.1016/j.earscirev.2014.10.005 |bibcode=2015ESRv..149...67C |hdl=1983/d2b89cc3-b0a8-41b5-a220-b3d7d75687e0 |access-date=14 January 2023|hdl-access=free }}</ref> particularly that of benthic organisms.<ref>{{cite journal |last1=Pietsch |first1=Carlie |last2=Mata |first2=Scott A. |last3=Bottjer |first3=David J. |date=1 April 2014 |title=High temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018214000583 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=399 |pages=98–113 |doi=10.1016/j.palaeo.2014.02.011 |bibcode=2014PPP...399...98P |access-date=2 April 2023|url-access=subscription }}</ref><ref name="OceanicAnoxiaAndTheEndPermianMassExtinction" /> Anoxia disappeared from shallow waters more rapidly than the deep ocean.<ref>{{Cite journal |last1=Algeo |first1=Thomas J. |last2=Chen |first2=Zhong Qiang |last3=Fraiser |first3=Margaret L. |last4=Twitchett |first4=Richard J. |date=15 July 2011 |title=Terrestrial–marine teleconnections in the collapse and rebuilding of Early Triassic marine ecosystems |url=https://www.sciencedirect.com/science/article/pii/S0031018211000149 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |series=Permian - Triassic ecosystems: collapse and rebuilding |volume=308 |issue=1 |pages=1–11 |doi=10.1016/j.palaeo.2011.01.011 |bibcode=2011PPP...308....1A |issn=0031-0182 |access-date=24 November 2023|url-access=subscription }}</ref> Reexpansions of oxygen-minimum zones did not cease until the late Spathian, periodically setting back and restarting the biotic recovery process.<ref>{{cite journal |last1=Tian |first1=Li |last2=Tong |first2=Jinnan |last3=Algeo |first3=Thomas J. |last4=Song |first4=Haijun |last5=Song |first5=Huyue |last6=Chu |first6=Daoliang |last7=Shi |first7=Lei |last8=Bottjer |first8=David J. |date=15 October 2014 |title=Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018214003733 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=412 |pages=68–79 |doi=10.1016/j.palaeo.2014.07.018 |bibcode=2014PPP...412...68T |access-date=8 May 2023|url-access=subscription }}</ref> The decline in continental weathering towards the end of the Spathian at last began ameliorating marine life from recurrent anoxia.<ref>{{Cite journal |last1=Song |first1=Haijun |last2=Wignall |first2=Paul Barry |last3=Tong |first3=Jinnan |last4=Song |first4=Huyue |last5=Chen |first5=Jing |last6=Chu |first6=Daoliang |last7=Tian |first7=Li |last8=Luo |first8=Mao |last9=Zong |first9=Keqing |last10=Chen |first10=Yanlong |last11=Lai |first11=Xulong |last12=Zhang |first12=Kexin |last13=Wang |first13=Hongmei |date=15 August 2015 |title=Integrated Sr isotope variations and global environmental changes through the Late Permian to early Late Triassic |url=https://www.sciencedirect.com/science/article/pii/S0012821X15003337 |journal=[[Earth and Planetary Science Letters]] |volume=424 |pages=140–147 |doi=10.1016/j.epsl.2015.05.035 |bibcode=2015E&PSL.424..140S |issn=0012-821X |access-date=24 November 2023}}</ref> In some regions of Panthalassa, pelagic zone anoxia continued to recur as late as the Anisian,<ref>{{Cite journal |last1=Muto |first1=Shun |last2=Takahashi |first2=Satoshi |last3=Yamakita |first3=Satoshi |last4=Suzuki |first4=Noritoshi |last5=Suzuki |first5=Nozomi |last6=Aita |first6=Yoshiaki |date=15 January 2018 |title=High sediment input and possible oceanic anoxia in the pelagic Panthalassa during the latest Olenekian and early Anisian: Insights from a new deep-sea section in Ogama, Tochigi, Japan |url=https://www.sciencedirect.com/science/article/pii/S0031018217304443 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=490 |pages=687–707 |doi=10.1016/j.palaeo.2017.11.060 |bibcode=2018PPP...490..687M |issn=0031-0182 |access-date=24 November 2023|url-access=subscription }}</ref> probably due to increased productivity and a return of aeolian upwelling.<ref>{{Cite journal |last1=Woods |first1=Adam D. |last2=Zonneveld |first2=John-Paul |last3=Wakefield |first3=Ryan |date=13 December 2023 |title=Hyperthermal-driven anoxia and reduced productivity in the aftermath of the Permian-Triassic mass extinction: a case study from Western Canada |journal=[[Frontiers in Earth Science]] |volume=11 |doi=10.3389/feart.2023.1323413 |doi-access=free |bibcode=2023FrEaS..1123413W |issn=2296-6463 }}</ref> Some sections show a rather quick return to oxic water column conditions, however, so for how long anoxia persisted remains debated.<ref>{{cite journal |last1=Li |first1=Guoshan |last2=Wang |first2=Yongbiao |last3=Shi |first3=Guang R. |last4=Liao |first4=Wei |last5=Yu |first5=Lixue |date=15 April 2016 |title=Fluctuations of redox conditions across the Permian–Triassic boundary—New evidence from the GSSP section in Meishan of South China |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821500560X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=448 |pages=48–58 |doi=10.1016/j.palaeo.2015.09.050 |bibcode=2016PPP...448...48L |access-date=26 May 2023|url-access=subscription }}</ref> The volatility of the Early Triassic sulphur cycle suggests marine life continued to face returns of euxinia as well.<ref>{{cite journal |last1=Schobben |first1=Martin |last2=Stebbins |first2=Alan |last3=Algeo |first3=Thomas J. |last4=Strauss |first4=Harald |last5=Leda |first5=Lucyna |last6=Haas |first6=János |last7=Struck |first7=Ulrich |last8=Korn |first8=Dieter |last9=Korte |first9=Christoph |date=15 November 2017 |title=Volatile earliest Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle turnover rate? |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018217301931 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=486 |pages=74–85 |doi=10.1016/j.palaeo.2017.02.025 |bibcode=2017PPP...486...74S |access-date=26 May 2023|url-access=subscription }}</ref>

Some scientists have challenged the anoxia hypothesis on the grounds that long-lasting anoxic conditions could not have been supported if Late Permian thermohaline ocean circulation conformed to the "thermal mode" characterised by cooling at high latitudes. Anoxia may have persisted under a "haline mode" in which circulation was driven by subtropical evaporation, although the "haline mode" is highly unstable and was unlikely to have represented Late Permian oceanic circulation.<ref name="ZhangEtAl2001">{{cite journal| vauthors =Zhang R, Follows MJ, Grotzinger JP, Marshall J| title =Could the Late Permian deep ocean have been anoxic?| journal =[[Paleoceanography and Paleoclimatology]]| volume =16| issue =3| pages =317–329| year =2001| doi =10.1029/2000PA000522| bibcode =2001PalOc..16..317Z| doi-access =free}}</ref>

Oxygen depletion via extensive microbial blooms also played a role in the biological collapse of not just marine ecosystems but freshwater ones as well. Persistent lack of oxygen after the extinction event itself helped delay biotic recovery for much of the Early Triassic epoch.<ref>{{cite journal |last1=Mays |first1=Chris |last2=McLoughlin |first2=Stephen |last3=Frank |first3=Tracy D. |last4=Fielding |first4=Christopher R. |last5=Slater |first5=Sam M. |last6=Vajda |first6=Vivi |date=17 September 2021 |title=Lethal microbial blooms delayed freshwater ecosystem recovery following the end-Permian extinction |journal=[[Nature Communications]] |volume=12 |issue=1 |page=5511 |doi=10.1038/s41467-021-25711-3 |pmid=34535650 |pmc=8448769 |bibcode=2021NatCo..12.5511M }}</ref>