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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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Neoproterozoic to early Phanerozoic rise in island arc redox state due to deep ocean oxygenation and increased marine sulfate levels

Abstract.

"A rise in atmospheric O2 levels between 800 and 400 Ma is thought to have oxygenated the deep oceans, ushered in modern biogeochemical cycles, and led to the diversification of animals. Over the same time interval, marine sulfate concentrations are also thought to have increased to near-modern levels. We present compiled data that indicate Phanerozoic island arc igneous rocks are more oxidized (Fe3+/ΣFe ratios are elevated by 0.12) vs. Precambrian equivalents. [...]"

Source: PNAS
Authors: Daniel A. Stolper and Claire E. Bucholz
DOI: 10.1073/pnas.1821847116

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Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic

Abstract.

"The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the 15N/14N ratio (δ15N) of foraminifera shell-bound organic matter from three sediment cores was high, indicating expanded water column suboxia and denitrification. [...]"

Source: Science
Authors: Emma R. Kast et al.
DOI: 10.1126/science.aau5784

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Proterozoic seawater sulfate scarcity and the evolution of ocean–atmosphere chemistry

Abstract.

"Oceanic sulfate concentrations are widely thought to have reached millimolar levels during the Proterozoic Eon, 2.5 to 0.54 billion years ago. Yet the magnitude of the increase in seawater sulfate concentrations over the course of the Eon remains largely unquantified. A rise in seawater sulfate concentrations has been inferred from the increased range of marine sulfide δ34S values following the Great Oxidation Event and was induced by two processes: enhanced oxidative weathering of sulfides on land, and the onset of marine sulfur redox cycling. [...]"

Source: Nature Geoscience
Authors: Mojtaba Fakhraee et al.
DOI: 10.1038/s41561-019-0351-5

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Limited oxygen production in the Mesoarchean ocean

Abstract.

"The Archean Eon was a time of predominantly anoxic Earth surface conditions, where anaerobic processes controlled bioessential element cycles. In contrast to “oxygen oases” well documented for the Neoarchean [2.8 to 2.5 billion years ago (Ga)], the magnitude, spatial extent, and underlying causes of possible Mesoarchean (3.2 to 2.8 Ga) surface-ocean oxygenation remain controversial. [...]"

Source: PNAS
Authors: Frantz Ossa Ossa et al.
DOI: 10.1073/pnas.1818762116

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