Ephemeral hypoxia reduces oxygen consumption in the Caribbean coral Orbicella faveolata

Oxygen concentrations in coastal waters have declined globally by 10% since the mid-twentieth century, and ocean warming will further reduce the solubility of oxygen in coastal habitats. Some nearshore reefs experience periodic hypoxic conditions due to eutrophication, especially during the wet season. Here, we determined the combined impacts of hypoxia and elevated temperature on the reef-building coral, Orbicella faveolata, by exposing corals to normoxic or hypoxic conditions and ambient or elevated temperatures. Oxygen consumption was monitored using closed-system respirometry. Corals within hypoxic conditions consumed 34% less oxygen relative to corals in normoxic conditions. Corals in the elevated temperature normoxic treatment experienced a 10% increase in oxygen consumption relative to the control. Corals exposed to both stressors simultaneously experienced a 62% reduction in oxygen consumption. These results suggest that increased temperature may exacerbate the negative effects of hypoxia on O. faveolata.

Dead Zones in the Oceans

As this chapter shows, the open oceans are also running out of dissolved oxygen as seen at Station Papa in the subarctic Pacific Ocean, thanks to work done on Canadian weather ships starting in the 1950s. Not only are areas of severe hypoxia, or oxygen minimum zones, expanding, but the level of dissolved oxygen in all oceans is decreasing. The open oceans are losing oxygen because of climate change. The warming of the oceans reduces the solubility of oxygen in water and stimulates oxygen use by respiring organisms. This chapter explores how climate change is also altering circulation and the mixing of oxygen into oxygen-poor waters. Even where oxygen remains above dead-zone levels, its depletion is another sign of how climate change is reshaping the biosphere. The expansion of low-oxygen water has shifted the habitats of fish and invertebrates, such as the giant squid, over thousands of miles, and has disrupted the nitrogen cycle of the entire biosphere. The chapter explains that because of oxygen depletion, biological production of the oceans may decline due to the loss of nitrogen, while release of a potent greenhouse gas (nitrous oxide) may increase.

Hydrogen Peroxide Production in an Electrochemical Flow-by Reactor using Gas Diffusion Electrodes Modified with Organic Redox Catalysts

This paper presents a proposal to use an electrochemical flow-by reactor for hydrogen peroxide electrogeneration using cathodes formed from the incorporation of organic redox catalysts (2-ethylanthraquinone, 2-tert-butylanthraquinone, alizarin, and azobenzene) in the structure of gas diffusion electrodes. These electrodes help circumvent the low solubility of oxygen in aqueous solutions. Organic redox catalysts, which typically contain quinone or azo groups in their structure, were added to the electrode mass in a 10% proportion. The electrodes were used to study the electrogeneration of hydrogen peroxide in situ, in an acid medium (0.1 mol L-1 H2SO4 and 0.1 mol L-1 K2SO4, pH 1), inside an electrochemical flow-by reactor. Comparative analysis among the different catalysts indicated that the best electrode for hydrogen peroxide electrogeneration was the gas diffusion electrode modified with 10% of 2-ethylanthraquinone. With an underflow rate of 200 L h-1, hydrogen peroxide was formed with a maximum yield of 998.12 mg L-1 after 2 h at -2.0 V vs Pt//Ag/AgCl, for which the energy consumption was 11.21 kWh kg-1. The use of the electrochemical flow-by reactor was much more efficient, in that it yielded higher concentrations of hydrogen peroxide with extremely low energy consumption, compared to that obtained when using an electrochemical cell. In addition, for ensuring appropriate usage of the electrodes, optimizing their potential for the maximum generation of hydrogen peroxide, and obtaining the highest efficiency for the reduction of oxygen, a fuzzy algorithm was developed to help support the user’s decision.

Anoxic bottom water condition during the Deccan volcanism: Multi-proxy evidences from a shallow marine sequence in Rajahmundry, SE India

<p>Major events like global anoxic episodes and mass extinctions are often associated with the eruption of Large Igneous Provinces (LIPs) in the geological past. The Deccan Trap eruption in the end-Cretaceous period in India forms the second-largest LIP and has often been causally linked to the Cretaceous-Paleogene Boundary (K/PgB) mass extinction event. To date, however, environmental reconstructions from pre- and post-volcanic sequences (infra- and inter-trappean, respectively) have mostly been qualitative and fragmentary and as a result, the effects of volcanism on the adjacent environmental conditions are still not well understood. Here, we present evidence of bottom water anoxia as a direct consequence of the Deccan volcanism. For this work, we analyzed major and trace element abundance, total organic carbon (TOC), bulk carbon isotope composition (δ<sup>13</sup>C<sub>org</sub>), and molecular characterization of organic matter (OM) from shallow marine trappean sediments in Rajahmundry, SE India, where the main volcanic episodes separating the infra- and inter-trappean sediments also encompass the K/PgB. The infra-trappean shows overall low TOC (<0.1%) and δ<sup>13</sup>C<sub>org </sub>(–26.3±0.4‰) values, with relatively higher concentrations of longer-chained n-alkane homologues and detrital elements (Al, Ti, Th, K) suggesting a larger contribution from terrestrial derived OM. Across volcanism, however, there is considerable decrease in terrigenous influx, as well as lowering in Pristane/Phytane ratios (<0.6) and enrichment in redox-sensitive elements like Mo, U, V and Co. This is also accompanied by contemporaneous increases in TOC (~0.6%) and δ<sup>13</sup>C<sub>org </sub>values (~3.9‰), suggesting that the change from oxic to sub-oxic or anoxic condition after the main volcanic episode led to increased OM burial and perturbations in the shallow marine carbon reservoir. Higher supply of micro-nutrient during this interval, as evidenced from enrichment in Ba, Fe, Ni and Zn possibly suggest that hydrothermal recycling and initial phases of eutrophication led to depletion in the bottom-water oxygen levels. Temperature increases due to CO<sub>2</sub> degassing from volcanism may have further decreased the solubility of oxygen in the sea-waters; however, further studies from the volcanic province are required to ascertain the underlying causes and extent of perturbations and ultimately, to better constrain the complex environmental feedbacks associated with the Deccan volcanism.</p>

Analysis of Corrosion Rate With Addition of Pumps in Commercial Steel in Sea Water Media

Corrosion or rusting is very common in metals is a decrease in the ability of a metal due to the environment or chemicals. Sea water is a corrosive environment for metals because it contains sodium chloride (NaCl), calcium sulfate (CaSO4), calcium carbonate (CaCO3), and dissolved oxygen (O2) which affect the corrosion process of the material. The presence of dissolved oxygen will cause the rate of corrosion in metals to increase with increasing oxygen content (O2), the solubility of oxygen in water is a function of pressure, temperature and chloride content. The process of corrosion is almost the same for all materials, especially in metals occurs slowly but surely, corrosion can cause a material to have a limited service life, where the material expected to be used for a long time turns out to have a shorter life span than the average usage life.

Titanium Production via Titanium Sulfide

A new metallurgical process via titanium sulfide from ilmenite is proposed and experimentally approved: It consists of several stages; 1) The ilmenite ore is exposed to gaseous CS2 to selectively sulfurize to FeS, which is wet-chemically removed. 2) The residual oxide is again exposed to CS2 to form TiS2. 3) TiS2 is electrochemically reduced to metallic Ti using molten CaCl2-CaS as an application of OS process. TiFeO3 was exposed to Ar-CS2 mixed gas flow at 1173 K to form the mixture of FeS+TiO2. FeS was easily separated by immersing in H2SO4 solution at 313 K. After recovery of TiO2, it was converted completely to TiS2 by the second sulfurization with CS2. TiS2 could be reduced to Ti powder by calciothermic reduction and simulteneous electrolysis in a CaS-CaCl2 melt for about 6 hours at 1173 K and 3.0 V. The impurity decreased to a low level such as 0.021 mass%S due to very small solubility of S in a-Ti. However, 1.06 mass%O remained because of wide solubility of oxygen in a-Ti and water contamination in initial CaCl2.

Oxygen/nitrogen-assisted embrittlement of titanium alloys exposed at elevated temperature

Due to high solubility of oxygen and nitrogen in titanium alloys, the influence of the diffusion zone on the macroscopic tensile properties of pre-oxidized annealed Ti-6Al-4V tensile specimens was examined at room temperature. Thin microtensile specimens were prepared with different thicknesses ranging from 100 µm to 500 µm and then exposed at 750°C for durations between 5 and 200h. A dedicated gripping technique was developed in the present study to investigate the brittleness of such pre-oxidized and ultrathin specimens at room temperature. Tensile testing was paired with digital image correlation techniques to assess both macroscopic deformation and full-field strain maps. High temperature pre-oxidation treatments significantly decreased the ductility of the specimen and the tensile strength of the materials (yield strength and ultimate tensile strength). Fractographic examinations revealed typical brittle fracture features in the oxygen/nitrogen-affected diffusion zone in the periphery of the cross-section while the fracture remained ductile in the core of the specimen for most of the specimens. Some specimens fully failed in a brittle manner for “(pre-ox. duration)1/2/thickness” configurations with ratio equal or higher than 0.45 h1/2.µm-1.

Оxygen solubility in melts of Ni – Co system at complex deoxidation by aluminium and silicon

Alloys of Ni – Co system are widely used in industry. Oxygen is one of the harmful impurities in these alloys; in metal it is present in dissolved form or in the form of nonmetallic inclusions. Getting the finished metal with a minimum oxygen concentration is one of the main tasks of production process of these alloys. With the complex deoxidation of the metal melt, the activity of oxides resulting from the deoxidation process is less than one, due to this, with the same content of deoxidizing elements, it is possible to obtain a metal with a lower oxygen concentration, therefore, more deeply deoxidized. At joint deoxidation with two deoxidizers, a stronger deoxidizer takes a predominant part in the reaction, however, if oxides of the deoxidizing elements form chemical compounds, it contributes to participation of a weaker deoxidizer in deoxidation process. A thermodynamic analysis of the joint influence of aluminum and silicon on the solubility of oxygen in the melts of Ni – Co system has been performed. Deoxidation reaction products may be formed as mullite (3Al2O3·2SiO2 ), and kyanite (Al2O3·SiO2 ). Presence of silicon in the melt enhances the deoxidizing ability of aluminum: insignificantly in the case of formation of compound 3Al2O3·2SiO2 and significantly in the case of formation of compound Al2O3·SiO2 . Oxygen solubility curves in the case of formation of compound Al2O3·SiO2 pass through a minimum, the position of which depends on the content of aluminum in the melt and doesn’t dependent on silicon content. Aluminum content in the minimum points is insignificantly reduced from nickel to cobalt as in the case of melts of Ni – Co–Al. Further additives of aluminum lead to an increase in oxygen concentration. Areas of compounds Al2O3 , 3Al2O3·2SiO2 , Al2O3·SiO2 and SiO2 depending on aluminum and silicon contents in the melt are determined. In melts of the Ni – Co system, the deoxidizing ability of aluminum and silicon increases with an increase in cobalt content in the melt. However, silicon enhances the deoxidizing ability of aluminum the weaker the higher cobalt content.