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

.. based on molybdenum isotopes


"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

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Fossil site shows impact of early Jurassic's low oxygen oceans


Using a combination of fossils and chemical markers, scientists have tracked how a period of globally low ocean-oxygen turned an Early Jurassic marine ecosystem into a stressed community inhabited by only a few species.

Source: Science Daily

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Evidence for rapid weathering response to climatic warming during the Toarcian Oceanic Anoxic Event


"Chemical weathering consumes atmospheric carbon dioxide through the breakdown of silicate minerals and is thought to stabilize Earth’s long-term climate. However, the potential influence of silicate weathering on atmospheric pCO2 levels on geologically short timescales (103–105 years) remains poorly constrained. Here we focus on the record of a transient interval of severe climatic warming across the Toarcian Oceanic Anoxic Event or T-OAE from an open ocean sedimentary succession from western North America. [...]"

Source: Scientific Reports
Authors: Theodore R. Them et al.
DOI: 10.1038/s41598-017-05307-y

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Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia


"The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth’s oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO2) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in pO2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE.  [...]"

Source: Nature Communications
Authors: Sarah J. Baker et al.
DOI: 10.1038/ncomms15018

Full article

Jurassic drop in ocean oxygen lasted a million years

"Dramatic drops in oceanic oxygen, which cause mass extinctions of sea life, come to a natural end - but it takes about a million years.

The depletion of oxygen in the oceans is known as "anoxia", and scientists from the University of Exeter have been studying how periods of anoxia end.

They found that the drop in oxygen causes more organic carbon to be buried in sediment on the ocean floor, eventually leading to rising oxygen in the atmosphere which ultimately re-oxygenates the ocean."

Source: University of Exeter
Contact: Alex Morrison

Full article

Effect of oxygen minimum zone formation on communities of marine protists


"Changes in ocean temperature and circulation patterns compounded by human activities are leading to oxygen minimum zone (OMZ) expansion with concomitant alteration in nutrient and climate active trace gas cycling. Here, we report the response of microbial eukaryote populations to seasonal changes in water column oxygen-deficiency using Saanich Inlet, a seasonally anoxic fjord on the coast of Vancouver Island British Columbia, as a model ecosystem. [...]"

Source: The ISME Journal 6
Authors: William Orsi et al.
DOI: 10.1038/ismej.2012.7

Full article

Positive Indian Ocean Dipole events prevent anoxia off the west coast of India


"The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, favoring very low oxygen concentrations in the surface waters during late boreal summer and fall. This yearly-recurring coastal hypoxia is more severe during some years, leading to coastal anoxia that has strong impacts on the living resources. In the present study, we analyze a 1/4◦ resolution coupled physical–biogeochemical regional oceanic simulation over the 1960–2012 period to investigate the physical processes influencing the oxycline interannual variability off the WCI, that being a proxy for the variability on the shelf in our model. [...]" 

Source: Bioggeosciences 14
Authors: Parvathi Vallivattathillam et al.
DOI: 10.5194/bg-14-1541-2017

Full article

Tropical dead zones and mass mortalities on coral reefs


"Oxygen-starved coastal waters are rapidly increasing in prevalence worldwide. However, little is known about the impacts of these “dead zones” in tropical ecosystems or their potential threat to coral reefs. We document the deleterious effects of such an anoxic event on coral habitat and biodiversity, and show that the risk of dead-zone events to reefs worldwide likely has been seriously underestimated. Awareness of, and research on, reef hypoxia is needed to address the threat posed by dead zones to coral reefs."


Source: Proceedings of the National Academy of Sciences of the United Stated of America (PNAS)
Authors: Andrew H. Altieri et al.
DOI: 10.1073/pnas.1621517114

Full article


Buoyancy-driven coastal current blocks ventilation of an anoxic fjord on the Pacific coast of Canada


"Shallow sills restrict the ventilation of deep coastal fjords. Dense oceanic water seaward of the sill and lower density water within the receiving basin are generally required for oxygenated water to cross the sill and descend deep into the fjord. Here, we use concurrent 10-year time series from current meters in the fjord and on the continental shelf to examine ventilation of the 120-m deep, anoxic inner basin of Effingham Inlet on the west coast of Vancouver Island. Whereas density currents traverse the 40 m-deep sill and flow into the inner basin at mid-depth at quasi-fortnightly tidal intervals, only five current intrusions descended to the bottom of the basin over the decade-long measurement period. [...]"

Source: Journal of Geophysical Research (JGR)
Authors: Richard E. Thomson et al.
DOI: 10.1002/2016JC012512

Full article

Iron entangled

Iron is an essential fuel for life in the oceans. The influence of this element on biogeochemistry — and nitrogen cycling in particular — varies across environments and time.



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