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Heterogenous oceanic redox conditions through the Ediacaran-Cambrian boundary limited the metazoan zonation

Abstract.

"Recent studies have enhanced our understanding of the linkage of oxygenation and metazoan evolution in Early Cambrian time. However, little of this work has addressed the apparent lag of animal diversification and atmospheric oxygenation during this critical period of Earth history. This study utilizes the geochemical proxy and N isotope record of the Ediacaran–Cambrian boundary preserved in intra-shelf basin, slope, and slope basin deposits of the Yangtze Sea to assess the ocean redox state during the Early Cambrian metazoan radiation. [...]"

Source: Scientific Reports
Authors: Junpeng Zhang, Tailiang Fan, Yuandong Zhang, Gary G. Lash, Yifan Li & Yue Wu
DOI: 10.1038/s41598-017-07904-3

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Rapid nitrous oxide cycling in the suboxic ocean

Abstract.

"Nitrous oxide (N2O) is a powerful greenhouse gas and a major cause of stratospheric ozone depletion, yet its sources and sinks remain poorly quantified in the oceans. We used isotope tracers to directly measure N2O reduction rates in the eastern tropical North Pacific. Because of incomplete denitrification, N2O cycling rates are an order of magnitude higher than predicted by current models in suboxic regions, and the spatial distribution suggests strong dependence on both organic carbon and dissolved oxygen concentrations. Furthermore, N2O turnover is 20 times higher than the net atmospheric efflux. The rapid rate of this cycling coupled to an expected expansion of suboxic ocean waters implies future increases in N2O emissions. [...]"

Source: Science (2015)
Authors: Andrew R. Babbin, Daniele Bianchi, Amal Jayakumar, Bess B. Ward
DOI:10.1126/science.aaa8380

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Dependence of nitrite oxidation on nitrite and oxygen in low-oxygen seawater

Abstract.

"Nitrite oxidation is an essential step in transformations of fixed nitrogen. The physiology of nitrite oxidizing bacteria (NOB) implies that the rates of nitrite oxidation should be controlled by concentration of their substrate, nitrite, and the terminal electron acceptor, oxygen. The sensitivities of nitrite oxidation to oxygen and nitrite concentrations were investigated using 15N tracer incubations in the Eastern Tropical North Pacific. Nitrite stimulated nitrite oxidation under low in situ nitrite conditions, following Michaelis-Menten kinetics, indicating that nitrite was the limiting substrate. [...]

Source: Geophysical Reasearch Letters
Authors: Xin Sun, Qixing Ji, Amal Jayakumar, Bess B. Ward
DOI: 10.1002/2017GL074355

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Intense molybdenum accumulation in sediments underneath a nitrogenous water column and implications for the reconstruction of paleo-redox conditions..

.. based on molybdenum isotopes

Abstract.

"The concentration and isotope composition of molybdenum (Mo) in sediments and sedimentary rocks are widely used proxies for anoxic conditions in the water column of paleo-marine systems. While the mechanisms leading to Mo fixation in modern restricted basins with anoxic and sulfidic (euxinic) conditions are reasonably well constrained, few studies have focused on Mo cycling in the context of open-marine anoxia. Here we present Mo data for water column particulate matter, modern surface sediments and a paleo-record covering the last 140,000 years from the Peruvian continental margin. Mo concentrations in late Holocene and Eemian (penultimate interglacial) shelf sediments off Peru range from ∼70 to 100 µg g−1, an extent of Mo enrichment that is thought to be indicative of (and limited to) euxinic systems. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: FlorianScholz, ChristopherSiebert, Andrew W.Dale, MartinFrank
DOI: https://doi.org/10.1016/j.gca.2017.06.048

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Constraining the rate of oceanic deoxygenation leading up to a Cretaceous Oceanic Anoxic Event (OAE-2: ~94 Ma)

Abstract.

"The rates of marine deoxygenation leading to Cretaceous Oceanic Anoxic Events are poorly recognized and constrained. If increases in primary productivity are the primary driver of these episodes, progressive oxygen loss from global waters should predate enhanced carbon burial in underlying sediments—the diagnostic Oceanic Anoxic Event relic. Thallium isotope analysis of organic-rich black shales from Demerara Rise across Oceanic Anoxic Event 2 reveals evidence of expanded sediment-water interface deoxygenation ~43 ± 11 thousand years before the globally recognized carbon cycle perturbation. [...]"

Source: Science Advances
Authors: Chadlin M. Ostrander, Jeremy D. Owens and Sune G. Nielsen
DOI: 10.1126/sciadv.1701020

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Study estimates oxygen loss in ancient global ocean

A loss of oxygen in global ocean seawater 94 million years ago led to a mass extinction of marine life that lasted for roughly half a million years.

Scientists have found several potential explanations for how the loss of oxygen happened. These could include enhanced volcanic activity, increased nutrients reaching the ocean, rising sea levels, and warming sea and surface temperatures. But to point a finger at any one cause (or several of them) requires knowing how fast the oxygen loss happened.

A new technique, developed by Arizona State University graduate student Chad Ostrander with colleagues at Wood Hole Oceanographic Institution (WHOI) and Florida State University (FSU), has put a timetable on the oxygen loss associated with this major ocean extinction event, which is known to science as Oceanic Anoxic Event 2.

Source: phys.org

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Water quality measurements in San Francisco Bay by the U.S. Geological Survey, 1969–2015

Abstract.

The U.S. Geological Survey (USGS) maintains a place-based research program in San Francisco Bay (USA) that began in 1969 and continues, providing one of the longest records of water-quality measurements in a North American estuary. Constituents include salinity, temperature, light extinction coefficient, and concentrations of chlorophyll-a, dissolved oxygen, suspended particulate matter, nitrate, nitrite, ammonium, silicate, and phosphate.

Source: Scientific Data
Authors: Tara S. Schraga & James E. Cloern
DOI: 10.1038/sdata.2017.98

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Climate change and ocean deoxygenation within intensified surface-driven upwelling circulations

Abstract.

"Ocean deoxygenation often takes place in proximity to zones of intense upwelling. Associated concerns about amplified ocean deoxygenation arise from an arguable likelihood that coastal upwelling systems in the world's oceans may further intensify as anthropogenic climate change proceeds. Comparative examples discussed include the uniquely intense seasonal Somali Current upwelling, the massive upwelling that occurs quasi-continuously off Namibia and the recently appearing and now annually recurring ‘dead zone’ off the US State of Oregon. [...]"

Source: The Royal Society
Author: Andrew Bakun
DOI: 10.1098/rsta.2016.0327

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Ocean ventilation and deoxygenation in a warming world: introduction and overview

Abstract.

"Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and turbulent mixing, (ii) reduced oxygenation through decreased oxygen solubility at higher surface temperature, and (iii) the effects of warming on biological production, respiration and remineralization. The potential socio-economic consequences of reduced oxygen levels on fisheries and ecosystems may be far-reaching and significant. [...]"

Source: The Royal Society
Authors: John G. Shepherd, Peter G. Brewer, Andreas Oschlies, Andrew J. Watson
DOI: 10.1098/rsta.2017.0240

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A model study of warming-induced phosphorus–oxygen feedbacks in open-ocean oxygen minimum zones on millennial timescales

Abstract.

"Observations indicate an expansion of oxygen minimum zones (OMZs) over the past 50 years, likely related to ongoing deoxygenation caused by reduced oxygen solubility, changes in stratification and circulation, and a potential acceleration of organic matter turnover in a warming climate. The overall area of ocean sediments that are in direct contact with low-oxygen bottom waters also increases with expanding OMZs. This leads to a release of phosphorus from ocean sediments. If anthropogenic carbon dioxide emissions continue unabated, higher temperatures will cause enhanced weathering on land, which, in turn, will increase the phosphorus and alkalinity fluxes into the ocean and therefore raise the ocean's phosphorus inventory even further. [...]"

Source: Earth System Dynamics
Authors: Daniela Niemeyer, Tronje P. Kemena, Katrin J. Meissner, and Andreas Oschlies
DOI: 10.5194/esd-8-357-2017

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