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No detectable Weddell Sea Antarctic Bottom Water export during the Last and Penultimate Glacial Maximum

Abstract.

"Weddell Sea-derived Antarctic Bottom Water (AABW) is one of the most important deep water masses in the Southern Hemisphere occupying large portions of the deep Southern Ocean (SO) today. While substantial changes in SO-overturning circulation were previously suggested, the state of Weddell Sea AABW export during glacial climates remains poorly understood. [...]"

Source: Nature Communications
Authors: Huang Huang et al.
DOI: 10.1038/s41467-020-14302-3

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Intensified ocean deoxygenation during the end Devonian mass extinction

Abstract.

"The end‐Devonian mass extinction (~359 Ma) substantially impacted marine ecosystems and shaped the roots of modern vertebrate biodiversity. Although multiple hypotheses have been proposed, no consensus has been reached about the mechanism inducing this extinction event. In this study, I/Ca ratio of carbonate was used to unravel the changes in local oxygen content of the upper water column during this critical interval. The Devonian‐Carboniferous boundary was recorded in two shallow water carbonate sections in South China. [...]"

Source: Geochemistry, Geophysics, Geosystems
Authors: Jiangsi Liu et al.
DOI: 10.1029/2019GC008614

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Stepwise Earth oxygenation is an inherent property of global biogeochemical cycling

Abstract.

"Oxygenation of Earth’s atmosphere and oceans occurred across three major steps during the Paleoproterozoic, Neoproterozoic, and Paleozoic eras, with each increase having profound consequences for the biosphere. Biological or tectonic revolutions have been proposed to explain each of these stepwise increases in oxygen, but the principal driver of each event remains unclear. Here we show, using a theoretical model, that the observed oxygenation steps are a simple consequence of internal feedbacks in the long-term biogeochemical cycles of carbon, oxygen, and phosphorus, and that there is no requirement for a specific stepwise external forcing to explain the course of Earth surface oxygenation. [...]"

Source: Science
Authors: Lewis J. Alcott et al.
DOI: 10.1126/science.aax6459

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Spatiotemporal redox heterogeneity and transient marine shelf oxygenation in the Mesoproterozoic ocean

Abstract.

"The Mesoproterozoic Era (1.6-1.0 Ga), long regarded as an interval of sluggish biotic evolution and persistently low atmospheric-oceanic oxygen levels, has become the subject of recent controversy regarding putative large-scale oxygenation events. In this study, we conducted a comprehensive investigation of redox, productivity, seawater sulfate concentrations, and hydrographic conditions for the ∼1.4-1.32-Ga Xiamaling Formation in the shallow Hougou and mid-depth Huangtugui sections in the Yanshan Basin (North China). [...]"

Source: Geochimica et Cosmochimica Acta
Authors: HaiyangWang et al.
DOI: 10.1016/j.gca.2019.11.028

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Oceanic organic carbon as a possible first-order control on the carbon cycle during the Bathonian–Callovian

Abstract.

"Oceans are the largest, readily exchangeable, superficial carbon reservoir; a current challenge in investigating past and present environments and predict future evolution relates to the role of oceanic carbon in regulating Earths' carbon cycle and climate. At least one paired δ13Ccarb-TOC decoupling event is noted in the Late Bathonian–Early Callovian. [...]"

Source: Global and Planetary Change
Authors: Ricardo L.Silva et al.
DOI: 10.1016/j.gloplacha.2019.103058


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Cretaceous Oceanic Anoxic Events prolonged by phosphorus cycle feedbacks

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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Anaerobic nitrogen cycling on a Neoarchaean ocean margin

Abstract.

"A persistently aerobic marine nitrogen cycle featuring the biologically mediated oxidation of ammonium to nitrate has likely been in place since the Great Oxidation Event (GOE) some 2.3 billion years ago. Although nitrogen isotope data from some Neoarchaean sediments suggests transient nitrate availability prior to the GOE, these data are open to other interpretations. [...]"

Source: Earth and Planetary Science Letters
Authors: C.Mettam et al.
DOI: 10.1016/j.epsl.2019.115800

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Linking the progressive expansion of reducing conditions to a stepwise mass extinction event in the late Silurian oceans

Abstract.

"The late Ludlow Lau Event was a severe biotic crisis in the Silurian, characterized by resurgent microbial facies and faunal turnover rates otherwise only documented during the "big five" mass extinctions. This asynchronous late Silurian marine extinction event preceded an associated positive carbon isotope excursion (CIE), the Lau CIE, although a mechanism for this temporal offset remains poorly constrained. [...]"

Source: GeoScienceWorld
Authors: Chelsie N. Bowman et al.
DOI: 10.1130/G46571.1

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Oxygen depletion in ancient oceans caused major mass extinction

"For years, scientists struggled to connect a mechanism to this mass extinction, one of the 10 most dramatic ever recorded in Earth's history. Now, researchers have confirmed that this event, referred to by scientists as the Lau/Kozlowskii extinction, was triggered by an all-too-familiar culprit: rapid and widespread depletion of oxygen in the global oceans. [...]"

Source: ScienceDaily

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Brief oxygenation events in locally anoxic oceans during the Cambrian solves the animal breathing paradox

Abstract.

"Oxygen is a prerequisite for all large and motile animals. It is a puzzling paradox that fossils of benthic animals are often found in black shales with geochemical evidence for deposition in marine environments with anoxic and sulfidic bottom waters. It is debated whether the geochemical proxies are unreliable, affected by diagenesis, or whether the fossils are transported from afar or perhaps were not benthic.  [...]"

Source: Scientific Reports
Authors: Tais W. Dahl et al.
DOI: 10.1038/s41598-019-48123-2

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