scholarly journals Geochemical consequences of oxygen diffusion from the oceanic crust into overlying sediments and its significance for biogeochemical cycles based on sediments of the northeast Pacific

2021 ◽  
Vol 18 (17) ◽  
pp. 4965-4984
Author(s):  
Gerard J. M. Versteegh ◽  
Andrea Koschinsky ◽  
Thomas Kuhn ◽  
Inken Preuss ◽  
Sabine Kasten
Keyword(s):  
Ocean Bottom ◽  
Reaction Products ◽  
Equatorial Pacific Ocean ◽  
Abstract Exchange ◽  
Geochemical Composition ◽  
Nitrate Consumption ◽  
Organic Carbon Burial ◽  
Suboxic Zone ◽  
Diffusive Fluxes ◽  
The Impact

Abstract. Exchange of dissolved substances at the sediment–water interface provides an important link between the short-term and long-term geochemical cycles in the ocean. A second, as yet poorly understood sediment–water exchange is supported by low-temperature circulation of seawater through the oceanic basement underneath the sediments. From the basement, upwards diffusing oxygen and other dissolved species modify the sediment, whereas reaction products diffuse from the sediment down into the basement where they are transported by the basement fluid and released to the ocean. Here, we investigate the impact of this “second” route with respect to transport, release and consumption of oxygen, nitrate, manganese, nickel and cobalt on the basis of sediment cores retrieved from the Clarion Clipperton Zone (CCZ) in the equatorial Pacific Ocean. We show that in this abyssal ocean region characterised by low organic carbon burial and sedimentation rates vast areas exist where the downward- and upward-directed diffusive fluxes of oxygen meet so that the sediments are oxic throughout. This is especially the case where sediments are thin or in the proximity of faults. Oxygen diffusing upward from the basaltic crust into the sediment contributes to the degradation of sedimentary organic matter. Where the sediments are entirely oxic, nitrate produced in the upper sediment by nitrification is lost both by upward diffusion into the bottom water and by downward diffusion into the fluids circulating within the basement. Where the oxygen profiles do not meet, they are separated by a suboxic sediment interval characterised by Mn2+ in the porewater. Where porewater Mn2+ in the suboxic zones remains low, nitrate consumption is low and the sediment continues to deliver nitrate to the ocean bottom waters and basement fluid. We observe that at elevated porewater manganese concentrations, nitrate consumption exceeds production and nitrate diffuses from the basement fluid into the sediment. Within the suboxic zone, not only manganese but also cobalt and nickel are released into the porewater by reduction of Mn oxides, diffusing towards the oxic–suboxic fronts above and below where they precipitate, effectively removing these metals from the suboxic zone and concentrating them at the two oxic–suboxic redox boundaries. We show that not only do diffusive fluxes in the top part of deep-sea sediments modify the geochemical composition over time but also diffusive fluxes of dissolved constituents from the basement into the bottom layers of the sediment. Hence, the palaeoceanographic interpretation of sedimentary layers should carefully consider such deep secondary modifications in order to prevent the misinterpretation of primary signatures.

scholarly journals Geochemical consequences of oxygen diffusion from the oceanic crust into overlying sediments and its significance for biogeochemical cycles based on sediments of the NE Pacific

2021 ◽  
Author(s):  
Gerard J. M. Versteegh ◽  
Andrea Koschinsky ◽  
Thomas Kuhn ◽  
Inken Preuss ◽  
Sabine Kasten
Keyword(s):  
Pore Water ◽  
Ocean Bottom ◽  
Reaction Products ◽  
Abstract Exchange ◽  
Geochemical Composition ◽  
Nitrate Consumption ◽  
Organic Carbon Burial ◽  
Suboxic Zone ◽  
Diffusive Fluxes ◽  
The Impact

Abstract. Exchange of dissolved substances at the sediment–water interface provides an important link between the short–term and long–term geochemical cycles in the ocean. A second, as yet poorly understood sediment–water exchange is supported by low–temperature circulation of seawater through the oceanic basement underneath the sediments. From the basement, upwards diffusing oxygen and other dissolved species modify the sediment whereas reaction products diffuse from the sediment down into the basement, where they are transported by the basement fluid and released to the ocean. Here, we investigate the impact of this “second” route with respect to transport, release and consumption of oxygen, nitrate, manganese, nickel, and cobalt on the basis of sediment cores retrieved from the Clarion Clipperton Zone (CCZ) in the equatorial Pacific Ocean. We show that in this abyssal ocean region characterised by low organic–carbon burial and sedimentation rates vast areas exist where the downward and upward directed diffusive fluxes of oxygen meet so that the sediments are oxic throughout. This is especially the case where sediments are thin or in the proximity of faults. Oxygen diffusing upward from the basaltic crust into the sediment contributes to the degradation of sedimentary organic matter. Where the oxygen profiles do not meet, they are separated by a suboxic sediment interval characterised by Mn2+ in the pore–water. Where the sediments are entirely oxic, nitrate produced in the upper sediment by nitrification is lost both by upward diffusion into the bottom water and by downward diffusion into the fluids circulating within the basement. Where pore–water manganese in the suboxic zones remains low, nitrate consumption is low and the sediment continues to deliver nitrate to the ocean bottom waters and basement fluid. We observe that at elevated pore–water manganese concentrations, nitrate consumption exceeds production and the basement becomes a nitrate source. Within the suboxic zone, not only manganese but also cobalt and nickel are released into the pore–water by reduction of oxides, diffuse towards the oxic/suboxic fronts above and below where they precipitate, effectively removing these metals from the suboxic zone and concentrating them at the oxic/suboxic redox boundaries. We show that not only diffusive fluxes in the top part of deep–sea sediments modify the geochemical composition over time, but also diffusive fluxes of dissolved constituents from the basement into the bottom layers of the sediment. Hence, paleoceanographic interpretation of sedimentary layers should carefully consider such deep secondary modifications in order to prevent misinterpretation as primary signatures.

scholarly journals Coastal versus open-ocean denitrification in the Arabian Sea

2006 ◽  
Vol 3 (3) ◽  
pp. 665-695 ◽  
Author(s):  
S. W. A. Naqvi ◽  
H. Naik ◽  
A. Pratihary ◽  
W. D’ Souza ◽  
P. V. Narvekar ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Nutrient Loading ◽  
Isotopic Fractionation ◽  
Coastal Region ◽  
Open Ocean ◽  
N2o Production ◽  
Coastal System ◽  
Nitrate Consumption ◽  
Suboxic Zone ◽  
Nitrate And Nitrite

Abstract. The Arabian Sea contains one of the three major open-ocean denitrification zones in the world. In addition, pelagic denitrification also occurs over the inner and mid-shelf off the west coast of India. The major differences between the two environments are highlighted using the available data. The perennial open-ocean system occupies two orders of magnitude larger volume than the seasonal coastal system, however, the latter offers more extreme conditions (greater nitrate consumption leading to complete anoxia). Unlike the open-ocean system, the coastal system seems to have undergone a change (i.e., it has intensified) over the past few decades presumably due to enhanced nutrient loading from land. The two systems also differ from each other with regard to the modes of nitrous oxide (N2O) production: in the open-ocean suboxic zone, an accumulation of secondary nitrite (NO2−) is invariably accompanied by depletion of N2O whereas in the coastal suboxic zone high NO2− and very high N2O concentrations frequently co-occur, indicating, respectively, net consumption and net production of N2O by denitrifiers. The extents of heavier isotope enrichment in the combined nitrate and nitrite (NO3−+NO2−) pool and in N2O in reducing waters appear to be considerably smaller in the coastal region, reflecting more varied sources/sinks and/or different isotopic fractionation factors.

Application of CFD-DSMC coupling method in micro-scale gas flow and combustion

2020 ◽  
Vol 34 (27) ◽  
pp. 2050301
Author(s):  
Shaoyi Suo ◽  
Linsong Jiang ◽  
Maozhao Xie
Keyword(s):  
Boundary Layer ◽  
Chemical Reaction ◽  
Wall Temperature ◽  
Slip Velocity ◽  
Gas Flow ◽  
Wall Slip ◽  
Reaction Products ◽  
Microscopic Method ◽  
Flow Heat ◽  
The Impact

The reversible elementary reaction mechanism of six components and seven steps of H2/O2 are applied by using a CFD-DSMC coupling iteration method to study the impact of boundary on flow, heat transfer and chemical reaction in a microtube. The microtube consists of a converging section and a straight section, which represents the gap on the contact surface of the pellets in porous media. It shows that after coupling, with the designed conditions in this paper, the influence of wall temperature is more obvious than that of wall slip velocity on the coupling results from the analysis of chemical reaction, yet the velocity field in the boundary layer is more affected by the wall slip velocity. In addition, the velocity in the central region of the flow decreases while the concentration of reaction products increases after coupling, due to the increasing of the velocity in the boundary layer and the influence of wall temperature, respectively. By the coupling of CFD-DSMC methods, more details and influence of the boundary can be considered, and the computational efficiency is higher than that of the single microscopic method.

scholarly journals In Design of an Ocean Bottom Seismometer Sensor: Minimize Vibration Experienced by Underwater Low-Frequency Noise

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3446 ◽  
Author(s):  
Xiaohan Wang ◽  
Shangchun Piao ◽  
Yahui Lei ◽  
Nansong Li
Keyword(s):  
Seismic Waves ◽  
Low Frequency ◽  
Sound Field ◽  
Average Density ◽  
Vibration Velocity ◽  
Frequency Noise ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Underwater Noise ◽  
The Impact

Ocean Bottom Seismometers (OBS) placed on the seafloor surface are utilized for measuring the ocean bottom seismic waves. The vibration of OBS excited by underwater noise on its surface may interfere with its measured results of seismic waves. In this particular study, an OBS was placed on the seabed, while ray acoustic theory was used to deduce the sound field distribution around the OBS. Then using this information, the analytical expression for the OBS vibration velocity was obtained in order to find various factors affecting its amplitude. The finite element computing software COMSOL Multiphysics® (COMSOL) was used to obtain the vibration response model of the OBS which was exposed to underwater noise. The vibration velocity for the OBS calculated by COMSOL agreed with the theoretical result. Moreover, the vibration velocity of OBS with different densities, shapes, and characters were investigated as well. An OBS with hemispherical shape, consistent average density as that of the seafloor, and a physical structure of double tank has displayed minimum amplitude of vibration velocity. The proposed COMSOL model predicted the impact of underwater noise while detecting the ocean bottom seismic waves with the OBS. In addition, it provides significant help for the design and optimization of an appropriate OBS.

Antioxidant properties of formula derived Maillard reaction products in colons of intrauterine growth restricted pigs

2016 ◽  
Vol 7 (6) ◽  
pp. 2582-2590 ◽  
Author(s):  
Ghada Elmhiri ◽  
Dounia Hamoudi ◽  
Samir Dou ◽  
Narges Bahi-Jaber ◽  
Julie Reygnier ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Maillard Reaction ◽  
Antioxidant Properties ◽  
Maillard Reaction Products ◽  
Reaction Products ◽  
Intrauterine Growth ◽  
The Impact ◽  
And Oxidative Stress

The present study has been conducted to evaluate the impact of the consumption of high MRP formula on changes in the microbiota and oxidative stress in the colon of IUGR piglets.

scholarly journals Detection of Arbuscular Mycorrhizal Fungi in the Roots of Strawberry Plants Fertilized with Organic Bioproducts

2012 ◽  
Vol 77 (1) ◽  
pp. 17-27 ◽  
Author(s):  
Anna Lisek ◽  
Lidia Sas Paszt ◽  
Beata Sumorok
Keyword(s):  
Plant Growth ◽  
Arbuscular Mycorrhizal Fungi ◽  
Nested Pcr ◽  
Mycorrhizal Fungi ◽  
Arbuscular Mycorrhizal ◽  
Am Fungi ◽  
Universal Primers ◽  
Mineral Fertilizers ◽  
Reaction Products ◽  
The Impact

Summary In organic farming, mineral fertilizers are replaced by various preparations to stimulate plant growth and development. Introduction of new biopreparations into horticultural production requires an assessment of their effects on the growth and yielding of plants. Among the important indicators of the impact on plants of beneficial microorganisms contained in bioproducts is determination of their effectiveness in stimulating the growth and yielding of plants. Moreover, confirmation of the presence of arbuscular mycorrhizal (AM) fungi in the roots and plant growth promoting rhizobacteria (PGPR) in the rhizosphere is also necessary. In addition to conventional methods, molecular biology techniques are increasingly used to allow detection and identification of AM fungi in plant roots. The aim of this study was identification and initial taxonomic classification of AM fungi in the roots of ‘Elkat’ strawberry plants fertilized with various biopreparations using the technique of nested PCR. Tests were performed on DNA obtained from the roots of ‘Elkat’ strawberry plants: not fertilized, treated with 10 different biopreparations, or fertilized with NPK. Amplification of the large subunit of ribosomal gene (LSU rDNA) was carried out using universal primers, and then, in the nested PCR reaction, primers specific for the fungi of the genera Glomus, Acaulospora, and Scutellospora were used. Colonization of strawberry roots by arbuscular mycorrhizal fungi was determined on the basis of the presence of DNA fragments of a size corresponding to the types of the fungi tested for. As a result of the analyses, the most reaction products characterizing AM fungi were found in the roots of plants treated with the preparation Florovit Eko. The least fragments characteristic of AM fungi were detected in the roots of plants fertilized with NPK, which confirms the negative impact of mineral fertilizers on the occurrence of mycorrhizal fungi in the roots of strawberry plants. The roots of plants fertilized with Tytanit differed from the control plants by the presence of one of the clusters of fungi of the genus Glomus and by the absence of a cluster of fungi of the genus Scutellospora. In the roots of plants treated with other biopreparations there were reaction products indicating the presence of fungi of the genera Glomus, Scutellospora and Acaulospora, like in the roots of the control plants. The results will be used to assess the suitability of microbiologically enriched biopreparations in horticultural production.

Modeling the impact of oceanic circulation and marine productivity on Cretaceous seafloor anoxia

2020 ◽  
Author(s):  
Yannick Donnadieu ◽  
Marie Laugie ◽  
Jean-Baptiste Ladant ◽  
François Raisson ◽  
Laurent Bopp
Keyword(s):  
Land Surface ◽  
Oceanic Circulation ◽  
Equatorial Pacific Ocean ◽  
Oxygen Minimum Zones ◽  
Tethys Sea ◽  
Marine Biogeochemistry ◽  
Anoxic Events ◽  
Marine Productivity ◽  
The Impact

<p>Oceanic anoxic events (OAEs) are abrupt events of widespread deposition of organic-rich sediments and extensive seafloor anoxia. Mechanisms usually invoked as drivers of oceanic anoxia are various and still debated today. They include a rise of the CO2 atmospheric level due to increased volcanic activity, a control by the paleogeography, changes in oceanic circulation or enhanced marine productivity. In order to assess the role of these mechanisms, we use an IPCC-class model, the IPSL-CM5A2 Earth System Model, which couples the atmosphere, land surface, and ocean components, this last one including sea ice, physical oceanography and marine biogeochemistry which allows to simulate oceanic oxygen.</p><p>We focus here on OAE2, which occurs during the Cretaceous at the Cenomanian-Turonian boundary (93.5 Ma), and is identified as a global event with evidence for seafloor anoxia in the Atlantic and Indian Oceans, the Southwest Tethys Sea and the Equatorial Pacific Ocean. Using a set of simulations from 115 to 70 Ma, we analyze the long-term paleogeographic control on oceanic circulation and consequences on oceanic oxygen concentration and anoxia spreading. Short-term controls such as an increase of pCO<sub>2</sub>, nutrients, or orbital configurations are also studied with a second set of simulations with a Cenomano-Turonian (90 Ma) paleogeographic configuration. The different simulated maps of oxygen are used to study the evolution of marine productivity and oxygen minimum zones as well as the spreading of seafloor anoxia, in order to unravel the interlocking of the different mechanisms and their specific impact on anoxia through space and time.</p>

scholarly journals Geochemical composition of sapropel in lakes: reflections of paleoenvironmental conditions and anthropogenic influence

2020 ◽  
Author(s):  
Jonas Satkūnas ◽  
Vaidotas Valskys ◽  
Gytautas Ignatavičius ◽  
Alma Grigienė
Keyword(s):  
Heavy Metals ◽  
Environmental Changes ◽  
Human Impacts ◽  
Chemical Elements ◽  
Wide Spectrum ◽  
Anthropogenic Activity ◽  
Chemical Compositions ◽  
Eutrophic Lakes ◽  
Geochemical Composition ◽  
The Impact

Abstract Geochemical and lithological parameters of sapropel in lakes, combined with pollen data and radiocarbon 14C datings, contain a wide spectrum of environmental information. This includes records of fluctuations of water level and changes of conditions of sedimentation, accumulation of organic matter and chemical elements due to climate change, human impacts and other environmental changes. Four lakes with different trophic states and anthropogenic pressures were chosen for this study in Lithuania. Lake Balsys has a mesotrophic state while Lakes Didžiulis, Salotė and Gineitiškės have eutrophic states. X-ray fluorescence spectrometry was used to analyse concentrations of chemical elements, loss-on-ignition to determine organic, mineral and carbonate matter, pollen analysis and radiocarbon dating were applied for determination of paleoenvironmental conditions and age of sediments. Results of this study demonstrated rather different chemical compositions of sapropels in these lakes. Human impacts are evident in the upper layers of sapropel in all lakes, however very specific and complex geochemical composition was determined in deeper layers of sapropel in the different lakes. Higher concentrations of elements like Cr and Zn are expected in deeper layers of sapropel and are attributed to lithogenic association of trace elements. Pb and Cu were detected in upper layers of sapropel which indicates the impact of anthropogenic activity. Sapropel of eutrophic lakes (Salotė and Gineitiškės) is enriched by high concentrations of heavy metals (galbūt naudoti tiesiog chemical elements?) (Pb, Cr, Cu, Zn). Their main source was multidimensional anthropogenic pollution leading to a biogenic-anthropogenic association of elements. Sapropel with low concentrations of heavy metals exhibits a different inter-association matrix because most of the elements tend to form lithogenic-clastogenic associations.

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