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Life on the edge: active microbial communities in the Kryos MgCl2-brine basin at very low water activity

Abstract.

"The Kryos Basin is a deep-sea hypersaline anoxic basin (DHAB) located in the Eastern Mediterranean Sea (34.98°N 22.04°E). It is filled with brine of re-dissolved Messinian evaporites and is nearly saturated with MgCl2-equivalents, which makes this habitat extremely challenging for life. The strong density difference between the anoxic brine and the overlying oxic Mediterranean seawater impedes mixing, giving rise to a narrow chemocline. [...]"

Source: The ISME Journal
Authors: Lea Steinle et al.
DOI: 10.1038/s41396-018-0107-z

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Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction

Abstract.

"Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. [...]"

Source: Science Advances
Authors: Feifei Zhan et al.
DOI:10.1126/sciadv.1602921

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Ocean euxinia and climate change "double whammy" drove the Late Ordovician mass extinction

Abstract.

"The Late Ordovician mass extinction (LOME, ca. 445 Ma) was the first of the "Big Five" Phanerozoic extinction events and comprised two extinction pulses. Proposed kill mechanisms include glacially induced global cooling and the expansion of water-column anoxia and/or euxinia (sulfidic conditions), but no general consensus has been reached with regard to the precise role of these mechanisms. [...]"

Source: Geology
Authors: Caineng Zou et al.
DOI: 10.1130/G40121.1

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A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Abstract.

"Emerging geochemical evidence suggests that the atmosphere-ocean system underwent a significant decrease in O2 content following the Great Oxidation Event (GOE), leading to a mid-Proterozoic ocean (ca. 2.0–0.8 Ga) with oxygenated surface waters and predominantly anoxic deep waters. The extent of mid-Proterozoic seafloor anoxia has been recently estimated using mass-balance models based on molybdenum (Mo), uranium (U), and chromium (Cr) enrichments in organic-rich mudrocks (ORM).  [...]"

Source: Geochimica et Cosmochimica Acta
Authors: Alex I.Sheen et al.
DOI: 10.1016/j.gca.2018.01.036

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A record of deep-ocean dissolved O2 from the oxidation state of iron in submarine basalts

Abstract.

"The oxygenation of the deep ocean in the geological past has been associated with a rise in the partial pressure of atmospheric molecular oxygen (O2) to near-present levels and the emergence of modern marine biogeochemical cycles. It has also been linked to the origination and diversification of early animals. [...]"

Source: Nature
Authors: Daniel A. Stolper
DOI: 10.1038/nature25009

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The Northern Gulf of Mexico During OAE2 and the Relationship Between Water Depth and Black Shale Development

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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Monitoring microbial responses to ocean deoxygenation in a model oxygen minimum zone

Abstract.

"Today in Scientific Data, two compendia of geochemical and multi-omic sequence information (DNA, RNA, protein) generated over almost a decade of time series monitoring in a seasonally anoxic coastal marine setting are presented to the scientific community. These data descriptors introduce a model ecosystem for the study of microbial responses to ocean deoxygenation, a phenotype that is currently expanding due to climate change."

Source: Scientific Data
Authors: Steven J. Hallam, Mónica Torres-Beltrán & Alyse K. Hawley
DOI: 10.1038/sdata.2017.158

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Oxic-anoxic regime shifts mediated by feedbacks between biogeochemical processes and microbial community dynamics

Abstract.

"Although regime shifts are known from various ecosystems, the involvement of microbial communities is poorly understood. Here we show that gradual environmental changes induced by, for example, eutrophication or global warming can induce major oxic-anoxic regime shifts. We first investigate a mathematical model describing interactions between microbial communities and biogeochemical oxidation-reduction reactions. [...]"

Source: Nature Communications
Authors: Timothy Bush et al.
DOI: 10.1038/s41467-017-00912-x

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The onset of widespread marine red beds and the evolution of ferruginous oceans

Abstract.

"Banded iron formations were a prevalent feature of marine sedimentation ~3.8–1.8 billion years ago and they provide key evidence for ferruginous oceans. The disappearance of banded iron formations at ~1.8 billion years ago was traditionally taken as evidence for the demise of ferruginous oceans, but recent geochemical studies show that ferruginous conditions persisted throughout the later Precambrian, and were even a feature of Phanerozoic ocean anoxic events. [...]"

Source: Nature Communications
Authors: Haijun Song et al.
DOI: 10.1038/s41467-017-00502-x

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Uranium isotope evidence for an expansion of marine anoxia during the end-Triassic extinction

Abstract.

"The end-Triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia, suggesting that anoxia played a role in suppressing marine biodiversity. However, global changes in ocean anoxia are difficult to quantify using proxies for local anoxia. Uranium isotopes (δ238U) in CaCO3 sediments deposited under locally well-oxygenated bottom waters can passively track seawater δ238U, which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238U(VI) relative to 235U(VI) in anoxic marine sediments. [...]"

Source: Geochemistry, Geophysics, Geosystems
Authors: Adam B. Jost et al.
DOI: 10.1002/2017GC006941

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