Historic oxygen depletion events in Earth's oceans
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]however, evidence is still missing.[clarify]
^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.
^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.
^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.
^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.
^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.
^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.
^"Impact from the Deep". Scientific American. October 2006.
An anoxicevent describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and...
event had two main pulses, the first being the Pliensbachian-Toarcian boundary event (PTo-E). The second, larger pulse, the Toarcian Oceanic Anoxic Event...
Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater...
Extinction Event, the Toarcian Oceanic AnoxicEvent, the Cenomanian-Turonian Oceanic AnoxicEvent, the Cretaceous-Palaeogene Extinction Event, and the Palaeocene-Eocene...
used in various contexts: Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved oxygen Anoxicevent, when the Earth's oceans...
longest-lasting anoxicevents in geologic time. The cause of the Hirnantian-Rhuddanian anoxicevent is uncertain. Like most global anoxicevents, an increased...
The Selli Event, also known as OAE1a, was an oceanic anoxicevent (OAE) of global scale that occurred during the Aptian stage of the Early Cretaceous...
spaced events here, as shown by the presence of two distinct anoxic shale layers. There is evidence that the Kellwasser event was a two-pulsed event, with...
started around 183 million years ago and is marked by the Toarcian Oceanic AnoxicEvent, a global episode of oceanic anoxia, ocean acidification, and elevated...
Smith (2000). "Synchrony between Early Jurassic extinction, oceanic anoxicevent, and the Karoo-Ferrar flood basalt volcanism". Geology. 28 (8): 747–750...
hypoxia from an anoxicevent. The event had a period in which dissolved oxygen in the Earth's oceans was depleted. The Taghanic event caused a very high...
mid-Cretaceous (becoming extinct during the late Cretaceous Cenomanian-Turonian anoxicevent), plesiosaurs throughout the entire period, and mosasaurs appearing in...
oceanic anoxicevents, including the Toarcian Oceanic AnoxicEvent, the Mid-Cenomanian Event, and the Cenomanian-Turonian Oceanic AnoxicEvent. It is sometimes...
but based on drillholes in Svalbard the defining early Aptian Oceanic AnoxicEvent 1a (OAE1a) was carbon isotope dated to 123.1±0.3 Ma, limiting the possible...
The Amadeus Event (OAE1c) was an oceanic anoxicevent (OAE). It occurred 106 million years ago (Ma), during the Albian age of the Cretaceous period, in...
Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen...
Western European Urgonian Stage. The Selli Event, also known as OAE1a, was one of two oceanic anoxicevents in the Cretaceous Period, which occurred around...
2002). "Oceanic anoxicevents and plankton evolution: Biotic response to tectonic forcing during the mid-Cretaceous: OCEANIC ANOXICEVENTS AND PLANKTON EVOLUTION"...
The Mulde event was an anoxicevent, and marked the second of three1 relatively minor mass extinctions (the Ireviken, Mulde, and Lau events) during the...
in the Triassic, before the Late Smithian crisis (a widespread ocean anoxicevent that may have allowed ichthyopterygians to dominate deeper waters and...
Aalenian. The Toarcian Age began with the Toarcian Oceanic AnoxicEvent, a major anoxicevent associated with marine extinctions and increased global temperatures...
significantly more affected by the Hangenberg event than by the Kellwasser event. The Hangenberg event was an anoxicevent marked by a layer of black shale, and...
The Paquier Event (OAE1b) was an oceanic anoxicevent (OAE) that occurred around 111 million years ago (Ma), in the Albian geologic stage, during a climatic...
Oxygenation Event. Thus laminated black shale by itself is a poor indicator of oxygen levels. Scientists must look instead for geochemical evidence of anoxic conditions...
OAE could refer to: Oceanic Anoxicevent, in which the Earth's oceans become completely depleted of oxygen below the surface levels. Orchestra of the Age...
thought to coincide with the global Early Aptian oceanic anoxicevent (known as OAE1a or the Selli Event, 125.0–124.6 Ma) that led to the deposition of black...
Climate change Anoxicevent Biodiversity loss Mass mortality event Cascade effect Cataclysmic pole shift hypothesis Climate change and civilizational...
an anoxicevent took place, called the Cenomanian-Turonian boundary event or the "Bonarelli event", that is associated with a minor extinction event for...
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