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Efficient recycling of nutrients in modern and past hypersaline environments

Abstract.

"The biogeochemistry of hypersaline environments is strongly influenced by changes in biological processes and physicochemical parameters. Although massive evaporation events have occurred repeatedly throughout Earth history, their biogeochemical cycles and global impact remain poorly understood. Here, we provide the first nitrogen isotopic data for nutrients and chloropigments from modern shallow hypersaline environments (solar salterns, Trapani, Italy) and apply the obtained insights to δ15N signatures of the Messinian salinity crisis (MSC) in the late Miocene. [...]"

Source: Scientific Reports
Authors: Y. Isaji et al.
DOI: 10.1038/s41598-019-40174-9

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Enhanced North Pacific deep-ocean stratification by stronger intermediate water formation during Heinrich Stadial 1

Abstract.

"The deglacial history of CO2 release from the deep North Pacific remains unresolved. This is due to conflicting indications about subarctic Pacific ventilation changes based on various marine proxies, especially for Heinrich Stadial 1 (HS-1) when a rapid atmospheric CO2 rise occurs. Here, we use a complex Earth System Model to investigate the deglacial North Pacific overturning and its control on ocean stratification. [...]"

Source: Nature Communications
Authors: X. Gong et al.
DOI: 10.1038/s41467-019-08606-2

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Deep‐sea oxygen depletion and ocean carbon sequestration during the last ice age

Abstract.

"Enhanced ocean carbon storage during the Pleistocene ice ages lowered atmospheric CO2 concentrations by 80 to 100 ppm relative to interglacial levels. Leading hypotheses to explain this phenomenon invoke a greater efficiency of the ocean's biological pump, in which case carbon storage in the deep sea would have been accompanied by a corresponding reduction in dissolved oxygen. We exploit the sensitivity of organic matter preservation in marine sediments to bottom water oxygen concentration to constrain the level of dissolved oxygen in the deep central equatorial Pacific Ocean during the last glacial period (18,000 – 28,000 years BP) to have been within the range of 20‐50 μmol/kg, much less than modern value of ca. 168 μmol/kg. [...]"

Source: Global Biogeochemical Cycles
Authors: Robert F. Anderson et al.
DOI: 10.1029/2018GB006049

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Mid-Holocene deepening of the Southeast Pacific oxycline

Abstract.

"This study presents new high resolution sedimentary δ15N records from piston cores collected within and outside the present-day eastern south Pacific oxygen minimum zone along a latitudinal transect from 3.5°S to 15°S. Radiocarbon dating of foraminifera and organic matter show that the cores cover the Holocene and the last deglaciation with high sedimentation rate allowing interpretations at millennial to centennial timescale. [...]"

Source: Global and Planetary Change
Authors: Elfi Mollier-Vogel et al.
DOI: 10.1016/j.gloplacha.2018.10.020

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Southern Hemisphere sea-surface temperatures during the Cenomanian–Turonian: Implications for the termination of Oceanic Anoxic Event 2

Abstract.

"Mesozoic oceanic anoxic events (OAEs) were major perturbations of the Earth system, associated with high CO2 concentrations in the oceans and atmosphere, high temperatures, and widespread organic-carbon burial. Models for explaining OAEs and other similar phenomena in Earth history make specific predictions about the role and pattern of temperature change, which can be tested through comparison with the geological record. Oceanic Anoxic Event 2 (OAE 2) occurred ~94 m.y. ago and is commonly considered as the type example of an OAE. [...]"

Source: Geology 
Authors: Stuart A. Robinson et al.
DOI: 10.1130/G45842.1

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Global warming today mirrors conditions leading to Earth's largest extinction event, study says

"More than two-thirds of life on Earth died off some 252 million years ago, in the largest mass extinction event in Earth's history.

Researchers have long suspected that volcanic eruptions triggered "the Great Dying," as the end of the Permian geologic period is sometimes called, but exactly how so many creatures died has been something of a mystery.

Now scientists at the University of Washington and Stanford believe their models reveal how so many animals were killed, and they see frightening parallels in the path our planet is on today.

Models of the effects of volcanic greenhouse gas releases showed the Earth warming dramatically and oxygen disappearing from its oceans, leaving many marine animals unable to breathe, according to a study published Thursday in the peer-reviewed journal Science. By the time temperatures peaked, about 80 percent of the oceans' oxygen, on average, had been depleted. Most marine animals went extinct. [...]"

Source: Phys.org

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Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction

Abstract.

"Climate change triggered by volcanic greenhouse gases is hypothesized to have caused the largest mass extinction in Earth’s history at the end of the Permian Period (~252 million years ago). Geochemical evidence provides strong support for rapid global warming and accompanying ocean oxygen (O2) loss, but a quantitative link among climate, species’ traits, and extinction is lacking. To test whether warming and O2 loss can mechanistically account for the marine mass extinction, we combined climate model simulations with an established ecophysiological framework to predict the biogeographic patterns and severity of extinction. Those predictions were confirmed by a spatially explicit analysis of the marine fossil record. [...]"

Source: Science
Authors: Justin L. Penn et al.
DOI: 10.1126/science.aat1327

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Major intensification of Atlantic overturning circulation at the onset of Paleogene greenhouse warmth

Abstract.

"During the Late Cretaceous and early Cenozoic the Earth experienced prolonged climatic cooling most likely caused by decreasing volcanic activity and atmospheric CO2 levels. However, the causes and mechanisms of subsequent major global warming culminating in the late Paleocene to Eocene greenhouse climate remain enigmatic. We present deep and intermediate water Nd-isotope records from the North and South Atlantic to decipher the control of the opening Atlantic Ocean on ocean circulation and its linkages to the evolution of global climate. [...]"

Source: Nature Communications
Authors: S. J. Batenburg et al.
DOI: 10.1038/s41467-018-07457-7

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Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction

Abstract.

"For this study, we generated thallium (Tl) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) of the Early Jurassic. The T-OAE, like other Mesozoic OAEs, has been interpreted as an expansion of marine oxygen depletion based on indirect methods such as organic-rich facies, carbon isotope excursions, and biological turnover. Our Tl isotope data, however, reveal explicit evidence for earlier global marine deoxygenation of ocean water, some 600 ka before the classically defined T-OAE. "

Source: PNAS
Authors: Theodore R. Them et al.
DOI: 10.1073/pnas.1803478115

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Global-ocean redox variations across the Smithian-Spathian boundary linked to concurrent climatic and biotic changes

Abstract.

"The Smithian-Spathian boundary (SSB) was an interval characterized by a major global carbon cycle perturbation, climatic cooling from a middle/late Smithian boundary hyperthermal condition, and a major setback in the recovery of marine necto-pelagic faunas from the end-Permian mass extinction. Although the SSB has been linked to changes in oceanic redox conditions, key aspects of this redox variation (e.g., duration, extent, and triggering mechanisms) and its relationship to coeval climatic and biotic changes remain unresolved. [...]"

Source: Earth-Science Reviews
Authors: Feifei Zhang et al.
DOI: 10.1016/j.earscirev.2018.10.012

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