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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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Chromium isotope cycling in the water column and sediments of the Peruvian continental margin

Abstract.

"Chromium (Cr) isotope fractionation is sensitive to redox changes and the Cr isotopic composition (δ53Cr) of sedimentary rocks has been used to reconstruct marine redox conditions and atmospheric oxygenation in the past. However, little is known about the behaviour of chromium isotopes across modern marine redox boundaries. We investigated Cr concentrations and δ53Cr variations in seawater and sediment across the Peruvian oxygen minimum zone (OMZ) to provide a better understanding of Cr cycling in the ocean. [...]"

Source: Geochimica et Cosmochimica
Authors: S. Bruggmann et al.
DOI: 10.1016/j.gca.2019.05.001

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High-resolution records of Oceanic Anoxic Event 2:

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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Multidecadal Changes in Marine Subsurface Oxygenation Off Central Peru During the Last ca. 170 Years

Abstract.

"Subsurface water masses with permanent oxygen deficiency (oxygen minimum zones, OMZ) are typically associated with upwelling regions and exhibit a high sensitivity to climate variability. Over the last decade, several studies have reported a global ocean deoxygenation trend since 1960 and a consequent OMZ expansion. However, some proxy records suggest an oxygenation trend for the OMZ over the margins of the Tropical North East Pacific since ca. 1850. [...]"

Source: Frontiers in Marine Science
Authors: Jorge Cardich et al.
DOI: 10.3389/fmars.2019.00270

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Oxygen minimum zone-type biogeochemical cycling in the Cenomanian-Turonian Proto-North Atlantic across Oceanic Anoxic Event 2

Abstract.

"Oceanic Anoxic Events (OAEs) in Earth's history are regarded as analogues for current and future ocean deoxygenation, potentially providing information on its pacing and internal dynamics. In order to predict the Earth system's response to changes in greenhouse gas concentrations and radiative forcing, a sound understanding of how biogeochemical cycling differs in modern and ancient marine environments is required. [...]"

Source: Earth and Planetary Science Letters
Authors: Florian Scholz et al.
DOI: 10.1016/j.epsl.2019.04.008

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Ammonium availability in the Late Archaean nitrogen cycle

Abstract.

"The bioavailability of essential nutrients such as nitrogen and phosphorus has fluctuated with the chemical evolution of Earth surface environments over geological timescales. However, significant uncertainty remains over the evolution of Earth’s early nitrogen cycle, particularly how and when it responded to the evolution of oxygenic photosynthesis. [...]"

Source: Nature Geoscience
Authors: J. Yang et al.
DOI: 10.1038/s41561-019-0371-1

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Periodic changes in the Cretaceous ocean and climate caused by marine redox see-saw

Abstract.

"Periodic changes in sediment composition are usually ascribed to insolation forcing controlled by Earth’s orbital parameters. During the Cretaceous Thermal Maximum at 97–91 Myr ago (Ma), a 37–50-kyr-long cycle that is generally believed to reflect obliquity forcing dominates the sediment record.  [...]"

Source: Nature Geoscience
Authors: Klaus Wallmann et al.
DOI: 10.1038/s41561-019-0359-x

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