Abstract.

"The Toarcian Oceanic Anoxic Event (T-OAE, Early Jurassic) is marked by widespread marine deoxygenation and deposition of organic carbon (OC)-rich strata. The genesis of the T-OAE is thought to be associated with environmental changes caused by the emission of 12C-enriched greenhouse gasses (CO2, CH4), manifested in a negative Toarcian carbon isotope excursion (nT-CIE). The nT-CIE is commonly used to stratigraphically define the T-OAE, and despite the complex interrelationship of the different environmental phenomena, both terms (nT-CIE and T-OAE) are commonly used interchangeable. [...]".

Source: Springer Nature
Authors: Wolfgang Ruebsam & Lorenz Schwark 
DOI: https://doi.org/10.1007/s00531-024-02408-8

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Full title: "The early Toarcian Oceanic Anoxic Event (Jenkyns Event) in the Alpine-Mediterranean Tethys, north African margin, and north European epicontinental seaway"

Abstract.

"The early Toarcian Oceanic Anoxic Event (Jenkyns Event) was associated with major world-wide climatic changes with profound effects on the global carbon cycle. This review revisits the available literature covering the Jenkyns Event applying an updated common stratigraphic definition, allowing illustration of the development and evolution of anoxia in the Alpine-Mediterranean Tethys [...]".

Source: Science Direct 
Authors: Gabriele Gambacorta et al.
DOI: https://doi.org/10.1016/j.earscirev.2023.104636

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Abstract.

"Fossils from the Araripe Basin (northeastern Brazil) are known for their remarkable preservation of vertebrates and invertebrates, even including soft tissues. They occur in carbonate concretions within organic carbon-rich strata assigned to the Romualdo Formation. Here we present integrated stable isotope, elemental and microfossil records from the Sítio Sobradinho outcrop, Araripe Basin, northeastern Brazil. Our results imply that black shales hosting fossil-bearing carbonate concretions within the lower Romualdo Formation were deposited during Oceanic Anoxic Event (OAE) 1b (Kilian sub-event). [...]".

Source: Wiley Online Library
Authors: Marlone H. H. Bom et al.
DOI: https://doi.org/10.1029/2023PA004736

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Abstract.

"The early Toarcian of the Early Jurassic saw a long-term positive carbon-isotope excursion (CIE) abruptly interrupted by a significant negative excursion (nCIE), associated with rapid global warming and an oceanic anoxic event (T-OAE, ∼183 Ma). However, the detailed processes and mechanisms behind widespread ocean deoxygenation are unclear. Here, we present high-resolution carbonate-associated sulfate sulfur-isotope [...]".

Source: Science Direct
Authors: Zhong Han et al.
DOI: https://doi.org/10.1016/j.epsl.2023.118404

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Abstract.

"This study provides a detailed examination of a condensed Cenomanian-Turonian (C-T) succession of two sections (Dokan Dam and Khalakan) in the Kurdistan Region, Northeastern Iraq, based on biostratigraphy (calcareous nannofossils and planktic foraminifera), carbon and oxygen isotope geochemistry, and facies analysis. The C/T boundary in this region is characterized by a hiatus noticeable due to the absence of the Globigerinelloides benthonensis and Dicarinella hagni subzones and the lack of positive carbon isotope excursion (CIE) peak b during the Oceanic Anoxic Event 2 (OAE2). [...]".

Source: Science Direct
Authors: Fadhil A. Lawa et al.
DOI: https://doi.org/10.1016/j.jafrearsci.2023.105064

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Abstract.

"Oceanic anoxic events (OAEs) represent discrete intervals of decreased marine oxygen concentrations often associated with volcanism, enhanced organic carbon burial coupled with positive δ13C excursions, and significant biotic turnover. Cretaceous OAE 2 (ca. 94 Mya) is especially notable for globally-distributed changes in calcareous invertebrate and plankton populations. While the presence of organic-rich facies is consistent with locally anoxic environments in many cases, determining the global extent of anoxia is more problematic. [...]".

Source: Science Direct
Authors: Joseph T. Kulenguski et al.
DOI: https://doi.org/10.1016/j.palaeo.2023.111756

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Full title: "Paleoenvironmental significance of the carbon isotope record across the Cenomanian–Turonian transition and the Oceanic Anoxic Event 2 (OAE2) in the southeastern Neotethys, Zagros, Iran"

Abstract.

"A high–resolution carbon isotope record of pelagic carbonates (δ13Ccarb) from the Zagros Mountains, Iran, documents a 1.8‰ positive carbon isotope excursion (CIE) in the southeastern Neotethys during the Cenomanian–Turonian transition, corresponding to Ocean Anoxic Event (OAE2). The succession is controlled by biostratigraphy that includes the Rotalipora cushmani [...]".

Source: Science Direct
Authors: Borhan Bagherpour et al.
DOI: https://doi.org/10.1016/j.cretres.2023.105574

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Abstract.

"Sea-level changes exert an important control on oceanic circulation and climate evolution. Researchers have proposed that sea-level rise favored accumulation of sediments enriched in organic carbon during oceanic anoxic events (OAEs), although high-frequency sea-level changes and their controlling mechanism have remained poorly constrained. Here we present a detailed sedimentological and geochemical study on Aptian (Lower Cretaceous) shallow-water carbonates of the Dariyan Formation exposed in the Zagros fold belt of southern Iran. [...]".

Source: Science Direct
Authors: Yiwei Xu et al.
DOI: https://doi.org/10.1016/j.gloplacha.2023.104236

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Abstract.

"The Cretaceous Oceanic Anoxic Event 2 (OAE2) is a greenhouse episode of severe marine anoxia at the Cenomanian-Turonian boundary. This time interval is characterized by rising sea surface temperature, enhanced marine biological productivity, and widespread occurrence of organic-rich black shales. With an export of biological production to the deep ocean, organisms consume vast amounts of oxygen and subsequently utilize nitrate and sulfate as electron acceptors in organic matter degradation, thereby affecting biogeochemical cycles of nitrogen and sulfur. [...]".

Source: Science Direct
Authors: Ruixiang Zhai et al.
DOI: https://doi.org/10.1016/j.gloplacha.2023.104182

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Abstract.

"At Site U1516 (Mentelle Basin, southeast Indian Ocean, offshore western Australia), the International Ocean Discovery Program (IODP) Expedition 369 recovered an almost complete pelagic record of the Upper Cretaceous, including the Oceanic Anoxic Event 2 (OAE 2). To better understand paleoenvironmental changes across OAE 2, 32 samples were analysed for benthic foraminiferal abundance data that represent one of the few benthic foraminiferal datasets spanning the OAE 2 in the southern high latitudes. [...]".

Source: Science Direct
Authors: Erik Wolfgring et al.
DOI: https://doi.org/10.1016/j.cretres.2023.105555

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Abstract.

"This paper reviews global records of anoxic events of the Middle Devonian – earliest Mississippian, as well as the possible triggers and controls of these events. These “anoxic events” are complex multistage paleoenvironmental disturbances manifested in multiple proxies, which we showcase with the Horn River Group (HRG) – a succession of basinal organic-rich shales and cherts deposited during the latest Eifelian – earliest Late Frasnian(∼386–373 My ago) on the western continental margin of Laurentia near the paleo-equator. [...]".

Source: Science Direct
Authors: Pavel Kabanov et al.
DOI: https://doi.org/10.1016/j.earscirev.2023.104415

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Abstract. 

"Oceanic Anoxic Events (OAEs) are important geological events that may be analogues to future climate-driven deoxygenation of our oceans. Much of the global ocean experienced anoxic conditions during the Cenomanian–Turonian OAE (OAE2; ∼94 Ma), whereas the Western Interior Seaway (WIS) experienced oxygenation at this time. Here, organic geochemical and palynological data generated from Cenomanian–Turonian age sediments from five sites in the WIS are used to investigate changing redox and ecological conditions across differing palaeoenvironments and palaeolatitudes. [...]".

Source: Science Direct
Authors: Libby J. Robinson et al.
DOI: https://doi.org/10.1016/j.palaeo.2023.111496

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Abstract. 

"Oceanic anoxic events (OAEs) are considered as periods of oxygen deficiency in many oceans; accompanied by accumulation of organic-rich black shales. Mesozoic anoxic events were recognized based on the presence of black shales that are rich in organic matter. The most significant anoxic events during the Mesozoic are the Early Toarcian, the Early Aptian, and the Cenomanian–Turonian. The less significant events are the Valanginian-Hauterivian, the Hauterivian-Barremian, the Aptian-Albian, the Late Albian, the Albian-Cenomanian, and the Coniacian-Santonian. [...]".

Source: Springer Nature
Authors: Tarek Anan & Adam El-Shahat 
DOI: https://doi.org/10.1007/978-3-030-95637-0_7

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Abstract. 

"The Cenomanian-Turonian (Late Cretaceous) climate warming was closely coupled to profound perturbations of biogeochemical cycles and ecosystems. The occurrence of organic matter-rich sediments across various depositional environments of the proto-North Atlantic hereby marks severe oxygen-deficient conditions, culminating in Oceanic Anoxic Event (OAE 2) at the Cenomanian/Turonian boundary. Here we combine bulk, isotope and molecular geochemical techniques to characterize trends in organic matter accumulation and its relationship to biogeochemical cycling (nitrogen, carbon) and marine phytoplankton community shifts [...]". 

Source: Science Direct
Authors: Wolfgang Ruebsam & Lorenz Schwark
DOI: https://doi.org/10.1016/j.gloplacha.2023.104117

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Abstract. 

"The impact of global climate events on local ecosystems can vary spatially. Understanding this potential heterogeneity can illuminate which environments will be most impacted and the proximal drivers of ecosystem responses. Cenomanian–Turonian marine deposits of the Western Interior Seaway (WIS) record paleoceanographic changes associated with the Greenhorn transgression and the onset of Oceanic Anoxic Event 2 (OAE2). They provide an ideal setting to study basin-wide paleoecological responses during a global perturbation. [...]".

Source: Cambridge University Press
Authors: Raquel Bryant & Christina L. Belanger
DOI: https://doi.org/10.1017/pab.2022.47

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Abstract.

"The late Pliensbachian to early Toarcian was characterized by major climatic and environmental changes, encompassing the early Toarcian Oceanic Anoxic Event (T-OAE, or Jenkyns Event, ∼183 Ma) and the preceding Pliensbachian–Toarcian boundary event (Pl/To). Information on seawater redox conditions through this time interval has thus far come mainly from European sections deposited in hydrographically restricted basins, and hence our understanding of the redox evolution of the open ocean (and in particular Panthalassa – the largest ocean to have existed) is limited. [...]".

Source: Science Direct 
Authors: Wenhan Chen et al.
DOI: https://doi.org/10.1016/j.epsl.2022.117959

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Abstract. 

"Ocean acidification causes biocalcification stress. The calcium isotope composition of carbonate producers can archive such stress because calcium isotope fractionation is sensitive to precipitation rate. Here, we synthesize morphometric observations of planktic foraminifera with multi-archive calcium isotope records from Gubbio, Italy and the Western Interior Seaway spanning Cretaceous Ocean Anoxic Event 2 (~94 million years ago). Calcium isotope ratios increase ~60 thousand years prior to the event. [...]". 

Source: Nature
Authors: Gabriella D. Kitch et al.
DOI: https://doi.org/10.1038/s43247-022-00641-0

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Abstract. 

"Oceanic Anoxic Events (OAEs) are conspicuous intervals in the geologic record that are associated with the deposition of organic carbon (OC)-rich marine sediment, linked to extreme biogeochemical perturbations, and characterized by widespread ocean deoxygenation. Mechanistic links between the marine biological carbon pump (BCP), redox conditions, and organic carbon burial during OAEs, however, remain poorly constrained. In this work we reconstructed the BCP in the western Tethys Ocean across OAE1a (~120 Mya) using sediment geochemistry and OC mass accumulation rates (OCAcc). [...]".

Source: Wiley Online Library
Authors: Kohen W. Bauer et al.
DOI: https://doi.org/10.1111/gbi.12538

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Abstract. 

"We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. [...]".

Source: Science Direct 
Authors: Thomas Steuber et al.
DOI: https://doi.org/10.1016/j.palaeo.2022.111086

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Abstract.

"Chromium is a redox sensitive element that exhibits a large range of isotopic compositions in Earth’s surface environments because of Cr(VI)-Cr(III) transformations. This property of Cr has been exploited as a tracer of Earth’s oxygenation history using marine sediments. However, paleoredox applications using Cr are difficult to implement due to its complicated cycling, which creates spatial variability in seawater δ53Cr values. Applications are further hindered by the potential for variability in the major inputs of Cr, such as submarine volcanism, to mask redox processes. [...]". 

Source: Science Direct 
Authors: Lucien Nana Yobo et al.
DOI: https://doi.org/10.1016/j.gca.2022.06.016

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Abstract. 

"The early Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) was characterized by marine deoxygenation and the burial of organic-rich sediments at numerous localities worldwide. However, the extent of marine anoxia and its impact on the sulfur cycle during the T-OAE is currently poorly understood. Here, stable sulfur isotopes of reduced metal-bound sulfur (δ34Spyrite) and pyrite sulfur concentrations (SPY) have been analyzed across the Pliensbachian-Toarcian boundary (Pl-To) and the T-OAE from the Sakahogi and Sakuraguchi-dani sections (Japan), which were deposited in the deep and shallow Panthalassic Ocean, respectively. [...]".

Source: Science Direct 
Authors: Wenhan Chen et al.
DOI: https://doi.org/10.1016/j.gloplacha.2022.103884

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Abstract.

"The Toarcian Oceanic Anoxic Event (T-OAE; ~ 183 Ma) represents an episode of marine anoxia that lasted for several hundred thousand years. Abiotic factorscontributing to the formation of the T-OAE, such as global warming, changes in weathering intensity, or sea-level change, are associated with a marked change in carbon cycling. While these factors are well studied, detailed palynological data, including marine and terrestrial palynomorphs, is still missing. Here we present comprehensive palynological data from the sedimentologically and geochemically well constrained T-OAE section in Dormettingen (SW Germany). [...]".

Source: Science Direct 
Authors: Francesca Galasso et al.
DOI: https://doi.org/10.1016/j.revpalbo.2022.104701

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Abstract. 

"The Cretaceous has been considered a “high-fire” world accompanied by widespread by-products of combustion in the rock record. The mid-Cretaceous oceanic anoxic event 1b (OAE1b) is marked by one of the major perturbations in the global carbon cycle characterized by deposition of organic-rich sediments in both marine and terrestrial settings. However, our understanding is still limited on changes in wildfire activity during OAE1b period. [...]".

Source: Science Direct 
Authors: Zhi-Hui Zhang et al.
DOI: https://doi.org/10.1016/j.jop.2022.06.002

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Abstract. 

"The Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, ca. 94 Ma) was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. Widespread deposition of organic-rich shales during OAE 2 has been attributed to a rapid rise in atmospheric CO2, global heating, and marine anoxia triggered by intense large igneous province (LIP) volcanism. Here, we present new Hg and Zn elemental and isotopic analyses from samples spanning OAE 2 in a hemipelagic section from Rehkogelgraben, Austria, which was part of the north-western Tethys. [...]".

Source: Science Direct 
Authors: Hanwei Yao et al.
DOI: https://doi.org/10.1016/j.gloplacha.2022.103881

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Abstract. 

"A δ238U record of changing ocean anoxia during OAE 2 is reconstructed using seawater derived U in pelagic marine sediments in the Portland #1 core in the south-central region of the Western Interior Seaway of North America. The peak negative excursion of 1.4‰ in authigenic sedimentary δ238U values is consistent with expansion of marine anoxia during the event, but the size of the shift is much larger than the negative excursions recorded in two other published records. [...]". 

Source: Science Direct 
Authors: Brayden S. McDonald et al.
DOI: https://doi.org/10.1016/j.gca.2022.05.010

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Abstract. 

"Understanding the causal mechanisms of past marine deoxygenation is critical to predicting the long-term Earth systems response to climate change. However, the processes and events preceding widespread carbon burial coincident with oceanic anoxic events remain poorly constrained. Here, we report a comprehensive biomarker inventory enveloping Oceanic Anoxic Event 2 that captures microbial communities spanning epipelagic to benthic environments in the southern proto-North Atlantic Ocean. We identify an abrupt, sustained increase in primary productivity that predates Oceanic Anoxic Event 2 by ∼220 ± 4 thousand years, well before other geochemical proxies register biogeochemical perturbations. [...]". 

Source: Communications Earth & Environment 
Authors: Gregory T. Connock et al. 
DOI: https://doi.org/10.1038/s43247-022-00466-x 

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Abstract. 

"During the mid-Cretaceous, the Earth experienced several environmental perturbations, including an extremely warm climate and Oceanic Anoxic Events (OAEs). Submarine volcanic episodes associated with formation of large igneous provinces (LIPs) may have triggered these perturbations. The osmium isotopic ratio (187Os/188Os) is a suitable proxy for tracing hydrothermal activity associated with the LIPs formation, but 187Os/188Os data from the mid-Cretaceous are limited to short time intervals. Here we provide a continuous high-resolution marine 187Os/188Os record covering all mid-Cretaceous OAEs. Several OAEs (OAE1a, Wezel and Fallot events, and OAE2) correspond to unradiogenic 187Os/188Os shifts, suggesting that they were triggered by massive submarine volcanic episodes. However, minor OAEs (OAE1c and OAE1d), which do not show pronounced unradiogenic 187Os/188Os shifts, were likely caused by enhanced monsoonal activity. [...]".

Source: Nature Communications 

Authors: Hironao Matsumoto et al.

DOI: https://doi.org/10.1038/s41467-021-27817-0

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Abstract.

"Oceanic anoxic events (OAEs) document major perturbations of the global carbon cycle with repercussions for the Earth's climate and ocean circulation that are relevant to understanding future climate trends. Here, we compare the onset and development of Cretaceous OAE1a and OAE2 in two drill cores with unusually high sedimentation rates from the Vocontian Basin (southern France) and Tarfaya Basin (southern Morocco). OAE1a and OAE2 exhibit remarkable similarities in the evolution of their carbon isotope (δ¹³C) records, with long-lasting negative excursions preceding the onset of the main positive excursions, supporting the view that both OAEs were triggered by massive emissions of volcanic CO₂ into the atmosphere. However, there are substantial differences, notably in the durations of individual phases within the δ¹³C positive excursions of both OAEs. [...]"

Source: Climate of the Past
Authors: Sebastian Beil et al.
DOI: 10.5194/cp-16-757-2020

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-Gulf of Mexico, NE Mexico

Abstract.

"Integrated microfacies and geochemical analyses conducted on five stratigraphic sections in northeastern Mexico (ancentral western margin of the proto-North Atlantic) reveal major paleoenvironmental changes in shallow water and pelagic environments in the prelude and run-up of the early Aptian oceanic anoxic event (OAE) 1a. During the Barremian–Aptian transition, the replacement of photozoan rudist-coral by mesotrophic/eutrophic orbitolinid-miliolid communities in the Cupido platform occurred in association with increased nutrient input. [...]"

Source: Cretaceous Research
Authors: Fernando Núñez-Useche et al.
DOI: 10.1016/j.cretres.2020.104488

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Abstract.

"Oceanic anoxic Event 2 (OAE-2) occurred at the Cenomanian-Turonian boundary (∼94.1 Ma) and was a time of profound global changes in ocean chemistry and the carbon cycle. This event was characterized by a positive carbon isotope excursion (CIE) caused by massive organic carbon burial, global greenhouse temperatures, ocean deoxygenation, and changes in ocean life driven by large igneous province (LIP) activity. LIPS throughout the Phanerozoic have had dynamic magma flux, with episodes of major eruptions interspersed with periods of relatively less intense eruptions. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: Daniel L. Sullivan et al.
DOI: 10.1016/j.gca.2020.04.002

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Abstract.

"The Toarcian Oceanic Anoxic Event (TOAE, Early Jurassic, ~182 Ma ago) was characterised by severe environmental perturbations which led to habitat degradation and extinction of marine species. Warming-induced anoxia is usually identified as main driver, but because marine life was also affected in oxygenated environments the role of raised temperature and its effects on marine life need to be addressed. [...]"

Source: Scientific Reports
Authors: Veronica Piazza et al.
DOI: 10.1038/s41598-020-61393-5

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Abstract.

"Cretaceous oceanic anoxic events (OAEs) were periods of geologically short (<1 million years) global change characterized by elevated temperatures, changes in ocean biogeochemistry, ecological turnover, and the global-scale deposition of black shales. After decades of OAE research, the intensity and spatiotemporal heterogeneity of ocean anoxia and its direct effects on marine ecology remain areas of active study. We present high-resolution organic geochemical and foraminiferal records from the western margin of the Western Interior Seaway (WIS) during the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2, ~94 Ma) that indicate reorganization of a neritic ecosystem in response to sea-level rise, and dynamic changes in redox conditions that were likely driven by enhanced marine productivity. [...]"

Source: Palaeogeography, Palaeoclimatology, Palaeoecology
Authors: F. Garrett Boudinot et al.
DOI: 10.1016/j.palaeo.2020.109673

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Abstract.

"The early Aptian Oceanic Anoxic Event (OAE) 1a represents a major perturbation of the Earth's climate system and in particular the carbon cycle, as evidenced by widespread preservation of organic matter in marine settings and a characteristic negative carbon isotopic excursion (CIE) at its onset, followed by a broad positive CIE. The contemporaneous emplacement of a large igneous province (LIP) is invoked as a trigger for OAE 1a (and OAEs in general), but this link and the ultimate source of the carbon perturbation at the onset of OAEs is still debated. [...]"

Source: 
Authors: Markus Adloff et al.
DOI: 10.1016/j.epsl.2019.115947

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Abstract.

"Oceanic Anoxic Events (OAEs) document major perturbations of the global carbon cycle with repercussions on the Earth’s climate and ocean circulation that are relevant to understand future climate trends. Here, we compare sedimentation patterns, nutrient cycling, organic carbon accumulation and carbon isotope variability across Cretaceous Oceanic Anoxic Events OAE1a and OAE2 in two drill cores with unusually high sedimentation rates from the Vocontian Basin (southern France) and Tarfaya Basin (southern Morocco). [...]"

Source: Climate of the Past (Preprint)
Authors: Sebastian Beil et al.
DOI: 10.5194/cp-2019-118

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Abstract.

"The proliferation of large, motile animals 540 to 520 Ma has been linked to both rising and declining O₂ levels on Earth. To explore this conundrum, we reconstruct the global extent of seafloor oxygenation at approximately submillion-year resolution based on uranium isotope compositions of 187 marine carbonates samples from China, Siberia, and Morocco, and simulate O₂ levels in the atmosphere and surface oceans using a mass balance model constrained by carbon, sulfur, and strontium isotopes in the same sedimentary successions. [...]"

Source: PNAS
Authors: Tais W. Dahl et al.
DOI: 10.1073/pnas.1901178116

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Insights into the timing, duration and extent of environmental perturbations from the palaeo-South Pacific Ocean

Abstract.

"Oceanic Anoxic Event 2 (OAE 2), which took place around the Cenomanian–Turonian boundary (∼94 Ma), is associated with extreme perturbations to the global carbon cycle, affected ocean basins worldwide and was associated with significant biological turnover. Although this event has been well studied in the northern hemisphere, the evolution and character of OAE 2, particularly in terms of the vertical and lateral extent of anoxia, is poorly constrained in the palaeo-Pacific Ocean. [...]"

Source: Earth and Planetary Science Letters
Authors: S. K. Gangl et al.
DOI: 10.1016/j.epsl.2019.04.028

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"The oceans are losing oxygen. Numerous studies based on direct measurements in recent years have shown this. Since water can dissolve less gas as temperatures rise, these results were not surprising. In addition to global warming, factors such as eutrophication of the coastal seas also contribute to the ongoing deoxygenation. [...]"

Source: Phys.org

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Abstract.

"Oceanic anoxic events have been associated with warm climates in Earth history, and there are concerns that current ocean deoxygenation may eventually lead to anoxia. Here we show results of a multi-millennial global-warming simulation that reveal, after a transitory deoxygenation, a marine oxygen inventory 6% higher than preindustrial despite an average 3 °C ocean warming. [...]"

Source: Nature Communications
Authors: Andreas Oschlies et al.
DOI: 10.1038/s41467-019-10813-w

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Abstract.

"The eastern Mediterranean Sea sedimentary record is characterised by intervals of organic rich sediment (sapropels), indicating periods of severe anoxia triggered by astronomical forcing. It has been hypothesized that nitrogen fixation was crucial in injecting the Mediterranean Sea with bioavailable nitrogen (N) during sapropel events. However, the evolution of the N biogeochemical cycle of sapropels is poorly understood. For example, the role of the complementary removal reaction, anaerobic ammonium oxidation (anammox), has not been investigated because the traditional lipid biomarkers for anammox, ladderane fatty acids, are not stable over long periods in the sedimentary record. [...]

Source: Biogeosciences
Authors: Darci Rush et al.
DOI: 10.5194/bg-2019-27

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Abstract.

"Mesozoic oceanic anoxic events (OAEs) were major perturbations of the Earth system, associated with high CO₂ concentrations in the oceans and atmosphere, high temperatures, and widespread organic-carbon burial. Models for explaining OAEs and other similar phenomena in Earth history make specific predictions about the role and pattern of temperature change, which can be tested through comparison with the geological record. Oceanic Anoxic Event 2 (OAE 2) occurred ~94 m.y. ago and is commonly considered as the type example of an OAE. [...]"

Source: Geology 
Authors: Stuart A. Robinson et al.
DOI: 10.1130/G45842.1

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Abstract.

"Ocean Anoxic Event 2 (OAE2) was a period of dramatic disruption to the global carbon cycle when massive amounts of organic matter (OM) were buried in marine sediments via complex and controversial mechanisms. Here we investigate the role of OM sulfurization, which makes OM less available for microbial respiration, in driving variable OM preservation in OAE2 sedimentary strata from Pont d’Issole (France). We find correlations between the concentration, S:C ratio, S-isotope composition, and sulfur speciation of OM suggesting that sulfurization facilitated changes in carbon burial at this site as the chemocline moved in and out of the sediments during deposition. [...]"

Source: Nature Communications
Authors: Morgan Reed Raven et al.
DOI: 10.1038/s41467-018-05943-6

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Abstract.

"The two major oceanic anoxic events of the Cretaceous, those of the Early Aptian (OAE 1a) and the Cenomanian–Turonian boundary (OAE 2), registered some of the highest temperatures reconstructed for the Cretaceous Period, and are thought to be related to the input of volcanically derived carbon dioxide from one or more Large Igneous Provinces. Widely distributed deposition of marine organic matter, the hallmark of OAEs, and intensified silicate weathering in response to a globally accelerated hydrological cycle and/or reaction of seawater with freshly extruded basalt, are both potential mechanisms whereby the content of atmospheric carbon dioxide could have been drawn down to promote cooling, on the assumption that this potential effect was not offset by increased addition of this volcanically derived greenhouse gas. [...]"

Source: Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences
Author: Hugh C. Jenkyns
DOI: 10.1098/rsta.2017.0073

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Summary.

"Nitrogen (N) cycling influences primary production in the ocean and, hence, the global climate. It is performed by a variety of microorganisms, including eukaryotes, bacteria and archaea in oxic, suboxic, and anoxic waters. Our knowledge of the reactions involved in marine N cycling and its associated microorganisms has greatly increased in the last decade due to the development of multiple culture-independent methods. Among them are gene and lipid biomarkers, which hold taxonomic potential and can be successfully applied in modern day and paleoenvironmental studies. However, many aspects of N cycling and their long-term implications for the marine environment and the global climate still require more study, especially in suboxic and anoxic waters, including the oxygen-deficient zones (ODZs), which are expanding in the modern oceans.

Author: Martina Sollai

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Abstract.

"Oceanic Anoxic Event 2 (OAE 2), occurring ∼94 million years ago, was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. It was typified by a rapid rise in atmospheric CO₂, global warming, and marine anoxia, leading to the widespread devastation of marine ecosystems. However, the precise timing and extent to which oceanic anoxic conditions expanded during OAE 2 remains unresolved. [...]"

Source: PNAS
Authors: Matthew O. Clarkson et al.
DOI: 10.1073/pnas.1715278115

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"A major study into an ancient climate change event that affected a significant percentage of Earth’s oceans has brought into sharp focus a lesser-known villain in global warming: oxygen depletion. 

The study, just published in the prestigious Proceedings of the National Academy of Sciences (PNAS), examined a past period of global warming around 94 million years ago, when oceans became de-oxygenated.

This famous period in Earth’s geological history, known as an Oceanic Anoxic Event (OAE), was more severe and on much longer timescales than the current changes. But it has given the scientists studying this period an extreme case-study to help understand how the oceans are effected by high atmospheric CO₂ emissions. [...]"

Source: University of Exeter News

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Abstract.

"Despite their name, Oceanic Anoxic Events (OAEs) are not periods of uniform anoxia and black shale deposition in ancient oceans. Shelf environments account for the majority of productivity and organic carbon burial in the modern ocean, and this was likely true in the Cretaceous as well. However, it is unlikely that the mechanisms for such an increase were uniform across all shelf environments. Some, like the northwest margin of Africa, were characterized by strong upwelling, but what might drive enhanced productivity on shelves not geographically suited for upwelling? [...]"

Source: Plaeoceanography
Authors: Christopher M. Lowery
DOI: 10.1002/2017PA003180

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"Animals need oxygen to survive, but a relative lack of oxygen in Earth’s ancient oceans helped early marine creatures evolve, a new study claims. Indeed, the “Cambrian explosion”—the burst of evolution about 540 million years ago that included the birth of most of the major animal groups we know today—was enabled by oxygen deprivation, the researchers say. The finding comes in the wake of a better understanding of how oxygen levels in the oceans and the atmosphere fluctuated in the deep past, and may shift how scientists think animal evolution can proceed. [...]"

Source: Science Magazine
Author: Lucas Joel
DOI: 10.1126/science.aar5252

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Abstract.

"Despite their name, Oceanic Anoxic Events (OAEs) are not periods of uniform anoxia and black shale deposition in ancient oceans. Shelf environments account for the majority of productivity and organic carbon burial in the modern ocean, and this was likely true in the Cretaceous as well. However, it is unlikely that the mechanisms for such an increase were uniform across all shelf environments. [...]"

Source: Paleoceanography
Authors: Christopher M. Lowery
DOI: 10.1002/2017PA003180

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Abstract.

"The rates of marine deoxygenation leading to Cretaceous Oceanic Anoxic Events are poorly recognized and constrained. If increases in primary productivity are the primary driver of these episodes, progressive oxygen loss from global waters should predate enhanced carbon burial in underlying sediments—the diagnostic Oceanic Anoxic Event relic. Thallium isotope analysis of organic-rich black shales from Demerara Rise across Oceanic Anoxic Event 2 reveals evidence of expanded sediment-water interface deoxygenation ~43 ± 11 thousand years before the globally recognized carbon cycle perturbation. [...]"

Source: Science Advances
Authors: Chadlin M. Ostrander, Jeremy D. Owens and Sune G. Nielsen
DOI: 10.1126/sciadv.1701020

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A loss of oxygen in global ocean seawater 94 million years ago led to a mass extinction of marine life that lasted for roughly half a million years.

Scientists have found several potential explanations for how the loss of oxygen happened. These could include enhanced volcanic activity, increased nutrients reaching the ocean, rising sea levels, and warming sea and surface temperatures. But to point a finger at any one cause (or several of them) requires knowing how fast the oxygen loss happened.

A new technique, developed by Arizona State University graduate student Chad Ostrander with colleagues at Wood Hole Oceanographic Institution (WHOI) and Florida State University (FSU), has put a timetable on the oxygen loss associated with this major ocean extinction event, which is known to science as Oceanic Anoxic Event 2.

Source: phys.org

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Summary:

Using a combination of fossils and chemical markers, scientists have tracked how a period of globally low ocean-oxygen turned an Early Jurassic marine ecosystem into a stressed community inhabited by only a few species.

Source: Science Daily

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Abstract.

"Little is known about the impact of the mid-Cretaceous Oceanic Anoxic Events (OAEs) on the neritic carbonate systems in South America. In order to fill this knowledge gap, the present paper reports on the record of environmental changes in the Albian–Turonian neritic carbonates from the western South American domain in Peru. Owing to the very expanded and well-exposed sections in the Oyon region of central Peru, the OAE 1d and 2 intervals were sampled at high temporal resolution for both bulk micrite and bulk organic matter carbon isotopes, allowing us to compare the fingerprint of these two events between the northern and central Peruvian regions.  [...]"

Source: Cretaceous Research Vol.75
Authors: J.P. Navarro-Ramirez et al.
DOI: 10.1016/j.cretres.2017.03.009

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