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A three-dimensional model of the marine nitrogen cycle during the Last Glacial Maximum constrained by sedimentary isotopes

Abstract.

"Nitrogen is a key limiting nutrient that influences marine productivity and carbon sequestration in the ocean via the biological pump. In this study, we present the first estimates of nitrogen cycling in a coupled 3D ocean-biogeochemistry-isotope model forced with realistic boundary conditions from the Last Glacial Maximum (LGM) ~21,000 years before present constrained by nitrogen isotopes. The model predicts a large decrease in nitrogen loss rates due to higher oxygen concentrations in the thermocline and sea level drop, and, as a response, reduced nitrogen fixation. Model experiments are performed to evaluate effects of hypothesized increases of atmospheric iron fluxes and oceanic phosphorus inventory relative to present-day conditions. [...]"

Source: Frontiers in Marine Science
Authors: Christopher J. Somes et al.
DOI: 10.3389/fmars.2017.00108

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Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic

Abstract.  

"In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (< 5 µmol O2 kg−1) show a lower carbon flux attenuation compared to well-oxygenated waters (> 100 µmol O2 kg−1), supposedly due to reduced heterotrophic activity. [...]"

Source: Biogeosciences 14
Authors: Anja Engel et al.
DOI: 10.5194/bg-14-1825-2017

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Response of western South American epeiric-neritic ecosystem to middle Cretaceous Oceanic Anoxic Events

Abstract.

"Little is known about the impact of the mid-Cretaceous Oceanic Anoxic Events (OAEs) on the neritic carbonate systems in South America. In order to fill this knowledge gap, the present paper reports on the record of environmental changes in the Albian–Turonian neritic carbonates from the western South American domain in Peru. Owing to the very expanded and well-exposed sections in the Oyon region of central Peru, the OAE 1d and 2 intervals were sampled at high temporal resolution for both bulk micrite and bulk organic matter carbon isotopes, allowing us to compare the fingerprint of these two events between the northern and central Peruvian regions.  [...]"

Source: Cretaceous Research Vol.75
Authors: J.P. Navarro-Ramirez et al.
DOI: 10.1016/j.cretres.2017.03.009

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Effects of low oxygen concentrations on aerobic methane oxidation in seasonally hypoxic coastal waters

Abstract. 

"Coastal seas may account for more than 75 % of global oceanic methane emissions. There, methane is mainly produced microbially in anoxic sediments from which it can escape to the overlying water column. Aerobic methane oxidation (MOx) in the water column acts as a biological filter, reducing the amount of methane that eventually evades to the atmosphere. The efficiency of the MOx filter is potentially controlled by the availability of dissolved methane and oxygen, as well as temperature, salinity, and hydrographic dynamics, and all of these factors undergo strong temporal fluctuations in coastal ecosystems. [...]"

Source: Biogeosciences 14
Authors: Lea Steinle et al.
DOI: 10.5194/bg-14-1631-2017

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The impact of ocean deoxygenation on iron release from continental margin sediments

Abstract. 

"In the oceans’ high-nitrate–low-chlorophyll regions, such as the Peru/Humboldt Current system and the adjacent eastern equatorial Pacific, primary productivity is limited by the micronutrient iron. Within the Peruvian upwelling area, bioavailable iron is released from the reducing continental margin sediments. The magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones. Here we show that measurements of molybdenum, uranium and iron concentrations can be used as a proxy for sedimentary iron release, and use this proxy to assess iron release from the sea floor beneath the Peru upwelling system during the past 140,000 years. [...]"

Source: Nature Geoscience 7
Authors: Florian Scholz et al.
DOI: 10.1038/ngeo2162

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Effect of oxygen minimum zone formation on communities of marine protists

Abstract.

"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

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West Maui shoreline water quality to be documented in huge collection program

"A groundbreaking scientific data collection program to expand the measuring of water quality off 18 West Maui shoreline sites has been forged between the state Department of Health and Maui community groups involved in the protection of the island’s nearshore waters. [...]"

Source: The Maui News

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

Abstract.

"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

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The influence of oxygen exposure time on the composition of macromolecular organic matter as revealed by surface sediments on the Murray Ridge

Abstract.

"The Arabian Sea represents a prime example of an open ocean extended oxygen minimum zone (OMZ) with low oxygen concentrations (down to less than 2 mM) between 200 and 1000 m water depth. The OMZ impinges on the ocean floor, affect ingorganic matter (OM) mineralization. We investigated impact of oxygen depletion on the composition of macromolecularOM (MOM) along a transect through the OMZ on the slopes of the Murray Ridge. This sub-marine high in the northern Arabian Sea, with the top at approximately 500 m below sea surface (mbss), intersects the OMZ. We analyzed sediments deposited in the core of OMZ (suboxic conditions) [...]"

Source: Geochimica et Cosmochimica Acta 206
Authors: Nierop, K.G.J.; Reichart, G.-J.; Veld, H.; Sinninghe Damsté, J.S
DOI: dx.doi.org/10.1016/j.gca.2017.02.032

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Remineralization of particulate organic carbon in an ocean oxygen minimum zone

Abstract.

"Biological oceanic processes, principally the surface production, sinking and interior remineralization of organic particles, keep atmospheric CO2 lower than if the ocean was abiotic. The remineralization length scale (RLS, the vertical distance over which organic particle flux declines by 63%, affected by particle respiration, fragmentation and sinking rates) controls the size of this effect and is anomalously high in oxygen minimum zones (OMZ). Here we show in the Eastern Tropical North Pacific OMZ 70% of POC remineralization is due to microbial respiration, indicating that the high RLS is the result of lower particle fragmentation by zooplankton, likely due to the almost complete absence of zooplankton particle interactions in OMZ waters. [...]"

Source: Nature Communications 8
Authors: E. L. Cavan, M. Trimmer, F. Shelley & R. Sanders
DOI: 10.1038/ncomms14847

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