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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

Read the full article here.


Investigating the effect of El Niño on nitrous oxide distribution in the eastern tropical South Pacific

Abstract.

"The open ocean is a major source of nitrous oxide (N2O), an atmospheric trace gas attributable to global warming and ozone depletion. Intense sea-to-air N2O fluxes occur in major oceanic upwelling regions such as the eastern tropical South Pacific (ETSP). The ETSP is influenced by the El Niño–Southern Oscillation that leads to inter-annual variations in physical, chemical, and biological properties in the water column. In October 2015, a strong El Niño event was developing in the ETSP; we conduct field observations to investigate (1) the N2Oproduction pathways and associated biogeochemical properties and (2) the effects of El Niño on water column N2O distributions and fluxes using data from previous non-El Niño years. [...]"

Source: Biogeosciences
Authors: Qixing Ji et al.
DOI: 10.5194/bg-16-2079-2019

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Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria

Abstract.

"Natural abundance of stable nitrogen (N) and oxygen (O) isotopes are invaluable biogeochemical tracers for assessing the N transformations in the environment. To fully exploit these tracers, the N and O isotope effects (15ε and 18ε) associated with the respective nitrogen transformation processes must be known. [...]"

Source: The ISME Journal
Authors: Kanae Kobayashi et al.
DOI: 10.1038/s41396-019-0440-x

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Identifying the origin of nitrous oxide dissolved in deep ocean by concentration and isotopocule analyses

Abstract.

"Nitrous oxide (N2O) contributes to global warming and stratospheric ozone depletion. Although its major sources are regarded as bacterial or archaeal nitrification and denitrification in soil and water, the origins of ubiquitous marine N2O maximum at depths of 100–800 m and N2O dissolved in deeper seawater have not been identified. [...]"

Source: Scientific Reports 
Authors: Sakae Toyoda et al.
DOI: 10.1038/s41598-019-44224-0

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The Equatorial Undercurrent and the Oxygen Minimum Zone in the Pacific

Abstract.

"Warming‐driven expansion of the oxygen minimum zone (OMZ) in the equatorial Pacific would bring very low oxygen waters closer to the ocean surface, and possibly impact global carbon/nutrient cycles and local ecosystems. Global coarse Earth System Models (ESMs) show, however, disparate trends that poorly constrain these future changes in the upper OMZ. [...]"

Source: Geophysical Research Letters
Authors: Julius J.M. Busecke, Laure Resplandy and John P. Dunne
DOI: 10.1029/2019GL082692

Read the full article here.


Diversity and relative abundance of ammonia- and nitrite-oxidizing microorganisms in the offshore Namibian hypoxic zone

Abstract.

"Nitrification, the microbial oxidation of ammonia (NH3) to nitrite (NO2) and NO2 to nitrate (NO3), plays a vital role in ocean nitrogen cycling. Characterizing the distribution of nitrifying organisms over environmental gradients can help predict how nitrogen availability may change with shifting ocean conditions, for example, due to loss of dissolved oxygen (O2). [...]"

Source: PLoS ONE
Authors: Evan Lau et al.
DOI: 10.1371/journal.pone.0217136

Read the full article here.


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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Diapycnal dissolved organic matter supply into the upper Peruvian oxycline

Abstract.

"The eastern tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZs) in the world ocean, where dissolved oxygen (O2) concentrations reach less than 1 µmol kg−1. [...]"

Source: Biogeosciences
Authors: Alexandra N. Loginova et al.
DOI: 10.5194/bg-16-2033-2019

Read the full article here.


Flooding Makes Big 'Dead Zone' Off Louisiana Coast Likely

"The year's widespread flooding has made it likely that a big, oxygen-starved "dead zone" off Louisiana's coast will form this summer, the head of the National Centers for Coastal Ocean Science said Thursday. Preliminary computer model runs "indicate a large to very large year," for the area where there's too little oxygen to support marine life, Steven Thur told the Mississippi River/Gulf of Mexico Hypoxia Task Force during a meeting livestreamed from Baton Rouge. [...]"

Source: The New York Times

Read the full article here.

 


Variations in ocean deoxygenation across Earth System Models: Isolating the role of parametrized lateral mixing

Abstract.

"Modern Earth System Models (ESMs) disagree on the impacts of anthropogenic global warming on the distribution of oxygen and associated low‐oxygen waters. A sensitivity study using the GFDL CM2Mc model points to the representation of lateral mesoscale eddy transport as a potentially important factor in such disagreement. Because mesoscale eddies are smaller than the spatial scale of ESM ocean grids, their impact must be parameterized using a lateral mixing coefficient AREDI. [...]"

Source: Global Biogeochemical Cycles
Authors: A. Bahl, A. Gnanadesikan and M.‐A. Pradal
DOI: 10.1029/2018GB006121

Read the full article here.


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

Read the full article here.


Vision is highly sensitive to oxygen availability in marine invertebrate larvae

Abstract.

"For many animals, evolution has selected for complex visual systems despite the high energetic demands associated with maintaining eyes and their processing structures. The metabolic demands of visual systems therefore make them highly sensitive to fluctuations in available oxygen. In the marine environment, oxygen changes over daily, seasonal, and inter-annual time scales and there are large gradients of oxygen with depth. [...]"

Source: Journal of Experimental Biology
Auhtors: Lillian R. McCormick, Lisa A. Levin and Nicholas W. Oesch
DOI: 10.1242/jeb.200899

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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

Read the full article here.


Strong intensification of the Arabian Sea oxygen minimum zone in response to Arabian Gulf warming

Abstract.

"The highly saline, oxygen saturated waters of the Arabian Gulf (hereafter the Gulf) sink to intermediate depths (200‐300m) when they enter the Arabian Sea, ventilating the World's thickest oxygen minimum zone (OMZ). Here, we investigate the impacts of a warming of the Gulf consistent with climate change projections on the intensity of this OMZ. Using a series of eddy‐resolving model simulations, we show that the warming of the Gulf waters increases their buoyancy and hence limits their contribution to the ventilation of intermediate depths. [...]"

Source: Geophysical Research Letters
Authors: Z. Lachkar, M. Lévy and S. Smith
DOI: 10.1029/2018GL081631

Read the full article here.


As oceans warm, microbes could pump more CO2 back into air, study warns

"The world's oceans soak up about a quarter of the carbon dioxide that humans pump into the air each year -- a powerful brake on the greenhouse effect. In addition to purely physical and chemical processes, a large part of this is taken up by photosynthetic plankton as they incorporate carbon into their bodies. When plankton die, they sink, taking the carbon with them. Some part of this organic rain will end up locked into the deep ocean, insulated from the atmosphere for centuries or more. [...]"

Source: EurekAlert!

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Complete arsenic-based respiratory cycle in the marine microbial communities of pelagic oxygen-deficient zones

Abstract.

"Marine oxygen-deficient zones (ODZs) are naturally occurring midlayer oxygen-poor regions of the ocean, sandwiched between oxygenated surface and deep layers. In the absence of oxygen, microorganisms in ODZs use other compounds, such as oxidized forms of nitrogen and sulfur, as terminal electron acceptors. [...]"

Source: PNAS
Authors: Jaclyn K. Saunders et al.
DOI: 10.1073/pnas.1818349116

Read the full article here.


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

Read the full article here.


Deep-sea sponge grounds as nutrient sinks: High denitrification rates in boreo-arctic sponges

Abstract.

"Sponges are commonly known as general nutrient providers for the marine ecosystem, recycling organic matter into various forms of bio-available nutrients such as ammonium and nitrate. In this study we challenge this view. We show that nutrient removal through microbial denitrification is a common feature in six cold-water sponge species from boreal and Arctic sponge grounds. [...]"

Source: Biogeosciences
Authors: Christine Rooks et al.
DOI: 10.5194/bg-2019-135

Read the full article here.


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