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Anoxic event

An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulfidic) waters.[1] Although anoxic events have not happened for millions of years, the geologic record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them.[2] These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating.[3] On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions.[4] Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO2) as the "central external trigger for euxinia."[5][6]

Human activities in the Holocene epoch, such as the release of nutrients from farms and sewage, cause relatively small-scale dead zones around the world. British oceanologist and atmospheric scientist Andrew Watson says full-scale ocean anoxia would take "thousands of years to develop."[7] The idea that modern climate change could lead to such an event is also referred to as Kump's hypothesis.[8]

  1. ^ Timothy W. Lyons; Ariel D. Anbar; Silke Severmann; Clint Scott & Benjamin C. Gill (January 19, 2009). "Tracking Euxinia in the Ancient Ocean: A Multiproxy Perspective and Proterozoic Case Study". Annual Review of Earth and Planetary Sciences. 37 (1): 507–53. Bibcode:2009AREPS..37..507L. doi:10.1146/annurev.earth.36.031207.124233.
  2. ^ Wignall, Paul B.; Richard J. Twitchett (24 May 1996). "Oceanic Anoxia and the End Permian Mass Extinction". Science. 5265. 272 (5265): 1155–1158. Bibcode:1996Sci...272.1155W. doi:10.1126/science.272.5265.1155. PMID 8662450. S2CID 35032406.
  3. ^ Peters, Walters; Modowan K.E. (2005). The Biomarker Guide, Volume 2: Biomarkers and Isotopes in the Petroleum Exploration and Earth History. Cambridge University Press. p. 749. ISBN 978-0-521-83762-0.
  4. ^ Ohkouchi, Naohiko; Kuroda, Junichiro; Taira, Asahiko (2015). "The origin of Cretaceous black shales: a change in the surface ocean ecosystem and its triggers". Proceedings of the Japan Academy, Series B. 91 (7): 273–291. Bibcode:2015PJAB...91..273O. doi:10.2183/pjab.91.273. PMC 4631894. PMID 26194853.
  5. ^ Meyer, Katja M.; Kump, Lee R. (2008). "Oceanic Euxinia in Earth History: Causes and Consequences". Annual Review of Earth and Planetary Sciences. 36: 251–288. Bibcode:2008AREPS..36..251M. doi:10.1146/annurev.earth.36.031207.124256.
  6. ^ Jurikova, Hana; Gutjahr, Marcus; Wallmann, Klaus; Flögel, Sascha; Liebetrau, Volker; Posenato, Renato; Angiolini, Lucia; Garbelli, Claudio; Brand, Uwe; Wiedenbeck, Michael; Eisenhauer, Anton (November 2020). "Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations" (PDF). Nature Geoscience. 13 (11): 745–750. Bibcode:2020NatGe..13..745J. doi:10.1038/s41561-020-00646-4. hdl:11573/1707839. S2CID 224783993.
  7. ^ Watson, Andrew J. (23 December 2016). "Oceans on the edge of anoxia". Science. 354 (6319): 1529–1530. Bibcode:2016Sci...354.1529W. doi:10.1126/science.aaj2321. hdl:10871/25100. PMID 28008026. S2CID 206653923.
  8. ^ "Impact from the Deep". Scientific American. October 2006.

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