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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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Intense molybdenum accumulation in sediments underneath a nitrogenous water column and implications for the reconstruction of paleo-redox conditions..

.. based on molybdenum isotopes

Abstract.

"The concentration and isotope composition of molybdenum (Mo) in sediments and sedimentary rocks are widely used proxies for anoxic conditions in the water column of paleo-marine systems. While the mechanisms leading to Mo fixation in modern restricted basins with anoxic and sulfidic (euxinic) conditions are reasonably well constrained, few studies have focused on Mo cycling in the context of open-marine anoxia. Here we present Mo data for water column particulate matter, modern surface sediments and a paleo-record covering the last 140,000 years from the Peruvian continental margin. Mo concentrations in late Holocene and Eemian (penultimate interglacial) shelf sediments off Peru range from ∼70 to 100 µg g−1, an extent of Mo enrichment that is thought to be indicative of (and limited to) euxinic systems. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: FlorianScholz, ChristopherSiebert, Andrew W.Dale, MartinFrank
DOI: https://doi.org/10.1016/j.gca.2017.06.048

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Fossil site shows impact of early Jurassic's low oxygen oceans

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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Evidence for rapid weathering response to climatic warming during the Toarcian Oceanic Anoxic Event

Abstract.

"Chemical weathering consumes atmospheric carbon dioxide through the breakdown of silicate minerals and is thought to stabilize Earth’s long-term climate. However, the potential influence of silicate weathering on atmospheric pCO2 levels on geologically short timescales (103–105 years) remains poorly constrained. Here we focus on the record of a transient interval of severe climatic warming across the Toarcian Oceanic Anoxic Event or T-OAE from an open ocean sedimentary succession from western North America. [...]"

Source: Scientific Reports
Authors: Theodore R. Them et al.
DOI: 10.1038/s41598-017-05307-y

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Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia

Abstract.

"The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth’s oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO2) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in pO2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE.  [...]"

Source: Nature Communications
Authors: Sarah J. Baker et al.
DOI: 10.1038/ncomms15018

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Jurassic drop in ocean oxygen lasted a million years

"Dramatic drops in oceanic oxygen, which cause mass extinctions of sea life, come to a natural end - but it takes about a million years.

The depletion of oxygen in the oceans is known as "anoxia", and scientists from the University of Exeter have been studying how periods of anoxia end.

They found that the drop in oxygen causes more organic carbon to be buried in sediment on the ocean floor, eventually leading to rising oxygen in the atmosphere which ultimately re-oxygenates the ocean."

Source: University of Exeter
Contact: Alex Morrison

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