Editing Permian–Triassic extinction event (section)

=== Hypercapnia and acidification ===
Marine organisms are more sensitive to changes in {{CO2}} (carbon dioxide) levels than terrestrial organisms for a variety of reasons. {{CO2}} is 28 times more [[Solubility|soluble]] in water than oxygen. Marine animals normally function with lower concentrations of {{CO2}} in their bodies than land animals, as the removal of {{CO2}} in air-breathing animals is impeded by the need for the gas to pass through the respiratory system's [[Biological membrane|membrane]]s ([[lung]]s' [[Pulmonary alveolus|alveolus]], [[Invertebrate trachea|tracheae]], and the like), even when {{CO2}} diffuses more easily than oxygen. In marine organisms, relatively modest but sustained increases in {{CO2}} concentrations hamper the synthesis of [[protein]]s, reduce fertilization rates, and produce [[Deformity|deformities]] in calcareous hard parts.<ref name="KNollBambach2007Paleophysiology" /> Higher concentrations of {{CO2}} also result in decreased activity levels in many active marine animals, hindering their ability to obtain food.<ref>{{cite journal |last1=Reddin |first1=Carl J. |last2=Nätscher |first2=Paulina |last3=Kocsis |first3=Ádám T. |last4=Pörtner |first4=Hans-Otto |last5=Kiessling |first5=Wolfgang |date=10 February 2020 |title=Marine clade sensitivities to climate change conform across timescales |url=https://www.nature.com/articles/s41558-020-0690-7?error=cookies_not_supported&code=a63948f1-abe4-434a-8ad5-962232192c04 |journal=[[Nature Climate Change]] |volume=10 |issue=3 |pages=249–253 |doi=10.1038/s41558-020-0690-7 |bibcode=2020NatCC..10..249R |s2cid=211074044 |access-date=26 March 2023|url-access=subscription }}</ref> An analysis of marine fossils from the Permian's final [[Changhsingian]] stage found that marine organisms with a low tolerance for [[hypercapnia]] (high concentration of carbon dioxide) had high extinction rates, and the most tolerant organisms had very slight losses. The most vulnerable marine organisms were those that produced calcareous hard parts (from calcium carbonate) and had low [[metabolic rate]]s and weak [[respiratory system]]s, notably [[calcareous sponge]]s, [[Rugose coral|rugose]] and [[tabulate coral]]s, [[calcite]]-depositing brachiopods, bryozoans, and [[echinoderm]]s; about 81% of such genera became extinct. Close relatives without [[calcareous]] hard parts suffered only minor losses, such as [[sea anemone]]s, from which modern corals evolved. Animals with high metabolic rates, well-developed respiratory systems, and non-calcareous hard parts had negligible losses except for [[conodont]]s, in which 33% of genera died out. This pattern is also consistent with what is known about the effects of [[Hypoxia (environmental)|hypoxia]], a shortage but not total absence of [[oxygen]]. However, hypoxia cannot have been the only killing mechanism for marine organisms. Nearly all of the [[continental shelf]] waters would have had to become severely hypoxic to account for the magnitude of the extinction, but such a catastrophe would make it difficult to explain the very selective pattern of the extinction. [[Mathematical models]] of the Late Permian and Early Triassic atmospheres show a significant but protracted decline in atmospheric oxygen levels, with no acceleration near the P–Tr boundary. Minimum atmospheric oxygen levels in the Early Triassic are never less than present-day levels and so the decline in oxygen levels does not match the temporal pattern of the extinction.<ref name="KNollBambach2007Paleophysiology" />

In addition, an increase in {{CO2}} concentration is inevitably linked to ocean acidification,<ref>{{cite journal |last1=Cui |first1=Ying |last2=Kump |first2=Lee R. |last3=Ridgwell |first3=Andy |date=1 November 2013 |title=Initial assessment of the carbon emission rate and climatic consequences during the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018213003969 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=389 |pages=128–136 |doi=10.1016/j.palaeo.2013.09.001 |bibcode=2013PPP...389..128C |access-date=26 June 2023|url-access=subscription }}</ref> consistent with the preferential extinction of heavily calcified taxa and other signals in the rock record that suggest a more [[acid]]ic ocean,<ref name="CalciumIsotopeConstraints">{{Cite journal |last1=Payne |first1=J. |last2=Turchyn |first2=A. |last3=Paytan |first3=A. |last4=Depaolo |first4=D. |last5=Lehrmann |first5=D. |last6=Yu |first6=M. |last7=Wei |first7=J. |year=2010 |title=Calcium isotope constraints on the end-Permian mass extinction |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=107 |issue=19 |pages=8543–8548 |bibcode=2010PNAS..107.8543P |doi=10.1073/pnas.0914065107 |pmc=2889361 |pmid=20421502 |doi-access=free}}</ref> such as a carbonate production crisis that occurred a few thousand years after volcanic greenhouse gas emissions began.<ref>{{Cite journal |last1=He |first1=Jiawei |last2=Hu |first2=Xiumian |last3=Li |first3=Juan |last4=Kemp |first4=David B. |last5=Hou |first5=Mingcai |last6=Han |first6=Zhong |date=15 November 2024 |title=Millennial-scale sedimentary evolution of carbonate platforms during the Permian–Triassic boundary hyperthermal event |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018224004449 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=654 |pages=112455 |doi=10.1016/j.palaeo.2024.112455 |bibcode=2024PPP...65412455H |access-date=13 October 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> The decrease in ocean pH is calculated to be up to 0.7 units.<ref name="OceanAcidificaton">{{cite journal |last1=Clarkson |first1=M. |last2=Kasemann |first2=S. |last3=Wood |first3=R. |last4=Lenton |first4=T. |last5=Daines |first5=S. |last6=Richoz |first6=S. |last7=Ohnemueller |first7=F. |last8=Meixner |first8=A. |last9=Poulton |first9=S. |last10=Tipper |first10=E. |display-authors=6 |date=2015-04-10 |title=Ocean acidification and the Permo-Triassic mass extinction |url=http://eprints.whiterose.ac.uk/85124/1/Clarkson_Boron_final.pdf |journal=[[Science (journal)|Science]] |volume=348 |issue=6231 |pages=229–232 |bibcode=2015Sci...348..229C |doi=10.1126/science.aaa0193 |pmid=25859043 |hdl=10871/20741 |s2cid=28891777}}</ref> An extreme [[aragonite sea]] formed.<ref>{{Cite journal |last1=Li |first1=Fei |last2=Yan |first2=Jiaxin |last3=Chen |first3=Zhong-Qiang |last4=Ogg |first4=James G. |last5=Tian |first5=Li |last6=Korngreen |first6=Dorit |last7=Liu |first7=Ke |last8=Ma |first8=Zulu |last9=Woods |first9=Adam D. |date=October 2015 |title=Global oolite deposits across the Permian–Triassic boundary: A synthesis and implications for palaeoceanography immediately after the end-Permian biocrisis |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825214002268 |journal=[[Earth-Science Reviews]] |language=en |volume=149 |pages=163–180 |doi=10.1016/j.earscirev.2014.12.006 |bibcode=2015ESRv..149..163L |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Ocean acidification was most extreme at mid-latitudes, and the major marine transgression associated with the end-Permian extinction is believed to have devastated shallow shelf communities in conjunction with anoxia.<ref name="LysoclineShoaling">{{cite journal |last1=Beauchamp |first1=Benoit |last2=Grasby |first2=Stephen E. |date=15 September 2012 |title=Permian lysocline shoaling and ocean acidification along NW Pangea led to carbonate eradication and chert expansion |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018212003586 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=350-352 |pages=73–90 |doi=10.1016/j.palaeo.2012.06.014 |bibcode=2012PPP...350...73B |access-date=2024-03-26|url-access=subscription }}</ref> Evidence from paralic facies spanning the Permian-Triassic boundary in western [[Guizhou]] and eastern [[Yunnan]], however, shows a local [[marine transgression]] dominated by carbonate deposition, suggesting that ocean acidification did not occur across the entire globe and was likely limited to certain regions of the world's oceans.<ref name="WignallEtAl2020">{{cite journal |last1=Wignall |first1=Paul Barry |last2=Chu |first2=Daoliang |last3=Hilton |first3=Jason M. |last4=Dal Corso |first4=Jacopo |last5=Wu |first5=Yuyang |last6=Wang |first6=Yao |last7=Atkinson |first7=Jed |last8=Tong |first8=Jinnan |date=June 2020 |title=Death in the shallows: The record of Permo-Triassic mass extinction in paralic settings, southwest China |journal=[[Global and Planetary Change]] |volume=189 |page=103176 |doi=10.1016/j.gloplacha.2020.103176 |bibcode=2020GPC...18903176W |s2cid=216302513 |doi-access=free }}</ref> One study, published in ''[[Scientific Reports]]'', concluded that widespread ocean acidification, if it did occur, was not intense enough to impede calcification and only occurred during the beginning of the extinction event.<ref>{{cite journal |last1=Foster |first1=William J. |last2=Hirtz |first2=J. A. |last3=Farrell |first3=C. |last4=Reistroffer |first4=M. |last5=Twitchett |first5=Richard J. |last6=Martindale |first6=R. C. |date=24 January 2022 |title=Bioindicators of severe ocean acidification are absent from the end-Permian mass extinction |journal=[[Scientific Reports]] |volume=12 |issue=1 |page=1202 |doi=10.1038/s41598-022-04991-9 |pmid=35075151 |pmc=8786885 |bibcode=2022NatSR..12.1202F }}</ref> The relative success of many marine organisms that were very vulnerable to acidification has further been used to argue that acidification was not a major extinction contributor.<ref>{{cite book |last1=Wignall |first1=Paul Barry |date=29 September 2015 |title=The Worst of Times: How Life on Earth Survived Eighty Million Years of Extinctions |chapter=The Killing Seas |location=Princeton |publisher=[[Princeton University Press]] |pages=83–84 |isbn=978-0-691-14209-8}}</ref> The persistence of highly elevated carbon dioxide concentrations in the atmosphere and ocean during the Early Triassic would have impeded the recovery of biocalcifying organisms after the PTME.<ref name="ElevatedAtmosphericCO2DelayedBioticRecovery">{{cite journal |last1=Fraiser |first1=Margaret L. |last2=Bottjer |first2=David P. |date=20 August 2007 |title=Elevated atmospheric CO2 and the delayed biotic recovery from the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018207001150 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=252 |issue=1–2 |pages=164–175 |doi=10.1016/j.palaeo.2006.11.041 |bibcode=2007PPP...252..164F |access-date=31 May 2023|url-access=subscription }}</ref>

Acidity generated by increased carbon dioxide concentrations in soil and sulphur dioxide dissolution in rainwater was also a kill mechanism on land.<ref>{{cite journal |last1=Heydari |first1=Ezat |last2=Arzani |first2=Nasser |last3=Hassanzadeh |first3=Jamshin |date=7 July 2008 |title=Mantle plume: The invisible serial killer — Application to the Permian–Triassic boundary mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018208002150 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=264 |issue=1–2 |pages=147–162 |doi=10.1016/j.palaeo.2008.04.013 |bibcode=2008PPP...264..147H |access-date=26 May 2023|url-access=subscription }}</ref> The increasing acidification of rainwater caused increased soil erosion as a result of the increased acidity of forest soils, evidenced by the increased influx of terrestrially derived organic sediments found in marine sedimentary deposits during the end-Permian extinction.<ref>{{cite journal |last1=Sephton |first1=Mark A. |last2=Jiao |first2=Dan |last3=Engel |first3=Michael H. |last4=Looy |first4=Cindy V. |last5=Visscher |first5=Henk |date=1 February 2015 |title=Terrestrial acidification during the end-Permian biosphere crisis? |url=https://pubs.geoscienceworld.org/gsa/geology/article/43/2/159/131802/Terrestrial-acidification-during-the-end-Permian |journal=[[Geology (journal)|Geology]] |volume=43 |issue=2 |pages=159–162 |doi=10.1130/G36227.1 |bibcode=2015Geo....43..159S |access-date=23 December 2022|hdl=10044/1/31566 |hdl-access=free }}</ref> Further evidence of an increase in soil acidity comes from elevated Ba/Sr ratios in earliest Triassic soils.<ref>{{cite journal |last1=Sheldon |first1=Nathan D.  |date=28 February 2006 |title=Abrupt chemical weathering increase across the Permian–Triassic boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018205005213 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=231 |issue=3–4 |pages=315–321 |doi=10.1016/j.palaeo.2005.09.001 |bibcode=2006PPP...231..315S |access-date=24 April 2023|url-access=subscription }}</ref> A positive feedback loop further enhancing and prolonging [[soil acidification]] may have resulted from the decline of infaunal invertebrates like tubificids and chironomids, which remove acid metabolites from the soil.<ref>{{cite journal |last1=Buatois |first1=Luis A. |last2=Borruel-Abadía |first2=Violeta |last3=De la Horra |first3=Raúl |last4=Galán-Abellán |first4=Ana Belén |last5=López-Gómez |first5=José |last6=Barrenechea |first6=José F. |last7=Arche |first7=Alfredo |date=25 March 2021 |title=Impact of Permian mass extinctions on continental invertebrate infauna |url=https://onlinelibrary.wiley.com/doi/full/10.1111/ter.12530 |journal=[[Terra Nova (journal)|Terra Nova]] |volume=33 |issue=5 |pages=455–464 |doi=10.1111/ter.12530 |bibcode=2021TeNov..33..455B |s2cid=233616369 |access-date=23 December 2022|url-access=subscription }}</ref> The increased abundance of vermiculitic clays in Shansi, South China coinciding with the Permian-Triassic boundary strongly suggests a sharp drop in soil pH causally related to volcanogenic emissions of carbon dioxide and sulphur dioxide.<ref>{{cite journal |last1=Xu |first1=Guozhen |last2=Deconinck |first2=Jean-François |last3=Feng |first3=Qinglai |last4=Baudin |first4=François |last5=Pellenard |first5=Pierre |last6=Shen |first6=Jun |last7=Bruneau |first7=Ludovic |date=15 May 2017 |title=Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018216302917 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=474 |pages=152–163 |doi=10.1016/j.palaeo.2016.07.036 |bibcode=2017PPP...474..152X |access-date=23 December 2022|url-access=subscription }}</ref> [[Hopane]] anomalies have also been interpreted as evidence of acidic soils and peats.<ref>{{cite journal |last1=Wang |first1=Chunjiang |date=January 2007 |title=Anomalous hopane distributions at the Permian–Triassic boundary, Meishan, China – Evidence for the end-Permian marine ecosystem collapse |url=https://www.sciencedirect.com/science/article/abs/pii/S0146638006002208 |journal=[[Organic Geochemistry]] |volume=38 |issue=1 |pages=52–66 |doi=10.1016/j.orggeochem.2006.08.014 |bibcode=2007OrGeo..38...52W |access-date=23 May 2023|url-access=subscription }}</ref> As with many other environmental stressors, acidity on land episodically persisted well into the Triassic, stunting the recovery of terrestrial ecosystems.<ref>{{cite journal |last1=Borruel-Abadía |first1=Violeta |last2=Barrenechea |first2=José F. |last3=Galán-Abellán |first3=Ana Belén |last4=De la Horra |first4=Raúl |last5=López-Gómez |first5=José |last6=Ronchi |first6=Ausonio |last7=Luque |first7=Francisco Javier |last8=Alonso-Azcárate |first8=Jacinto |last9=Marzo |first9=Mariano |date=20 June 2019 |title=Could acidity be the reason behind the Early Triassic biotic crisis on land? |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254119301597 |journal=[[Chemical Geology]] |volume=515 |pages=77–86 |doi=10.1016/j.chemgeo.2019.03.035 |bibcode=2019ChGeo.515...77B |s2cid=134704729 |access-date=18 December 2022|url-access=subscription }}</ref>