Oxygen from seawater

Solution Cathodic protection is widely used to protect immersed metallic structures from corrosion. When this technique is applied, in the range of—0.8 to —1.2 V (SCE), dissolved oxygen from seawater reduces onto metallic surface according to... 

F.18 Until we find an economical way of extracting oxygen from seawater or lunar rocks, we have to carry it with us to inhospitable places and do so in compressed form in tanks. A sample of oxygen... 

In an attempt to scavenge pure oxygen directly from seawater, Aquanautics Corp. [26] has developed a process similar to that of Roberts. In the Aquanautics scheme, the solution containing the carrier (in this case, a linear pentadentade polyalkylamine chelate of Fe or Co) flows through both anode and cathode of the electrochemical cell. 

Plants developed from photosynthetic bacteria. As we have explained in Chapters 5 and 6, bacteria could evolve on the top surface of the Earth by increasing their ability to capture light (energy) and by obtaining and using more effectively 15-20 elements from seawater, later the seabed and land, and with three or four from the atmosphere, while utilising novel chemistry. The need to adapt to oxygen later forced the development of compartments already seen in differentiated ... 

Boetius and Suess (2004) note that clams, mussels, and tubeworms have distinct adaptations to obtain oxygen from the seawater and sulfide from the sediments. If fluid flow is reduced so that sulfide does not reach the seafloor, these communities are replaced by specially adapted faunas, such as Acharax, that are... 

Oxidation of DMS to DMSO and DMSO. DMS is chemically and biochemically oxidized to dimethylsulfoxide (DMSO). Mechanisms for the in situ oxidation of DMS to DMSO in seawater have received little attention, even though this may be an important sink for DMS. Hydrogen peroxide occurs in surface oceanic waters (22) and is produced by marine algae (98). It may participate in a chemical oxidation of DMS, since peroxide oxidizes sulfides to sulfoxides (991. Photochemical oxidation of DMS to DMSO occurs in the atmosphere and DMSO is found in rain from marine regions (681. DMS is also photo-oxygenated in aqueous solution to DMSO if a photosensitizer is present natural compounds in coastal seawater catalyzed photo-oxidation at rates which may be similar to those at which DMS escapes from seawater into the atmosphere (1001. 

Much of what is currently understood about the Cenozoic history, of deep-sea temperature, carbon chemistry, and global ice volume, has been gleaned from the stable isotope ratios of benthic foraminifera. Benthic foraminifera extract carbonate and other ions from seawater to construct their tests. In many species, this is achieved near carbon and oxygen isotopic equilibrium. Kinetic fractionation effects tend to be small and constant (Grossman, 1984, 1987). As a result, shell fi C and strongly covary with the isotopic... 

It is quite likely that precipitation of quartz in shallow-water Paleoproterozoic iron formations occurred directly from seawater or from a siliceous gel without complicated intermediate steps. Winter and Knauth s (1992) isotopic evidence for this is presented below. Knauth (1994) pointed out that experiments by Mackenzie and Gees (1971) show that direct precipitation of quartz from seawater is possible at room temperature, and he believes that extraordinary hydrothermal circulation systems are not required to explain the observed characteristics of iron formations. One explanation of the oxygen isotope data for chert, discussed below, is that Earth-surface temperatmes during... 

DIP. As with the previously described difference methods, a pellet from a separate split is subjected to oxidation/hydrolysis for determination of TDP, and DOP is derived by difference. This method has also been adapted for use in concentrating DOP for isotopic studies of phosphate oxygen in seawater (see Section 8.13.3.3.3 Cohnan, 2002). 

It has been inferred from carbon and sulfur dating that the concentration of oxygen in the Earth s atmosphere was less than I part per million volume (ppmv) prior to around 2.4 billion (Ga) years ago, whereas methane would have been present at levels of around 10 to 10 ppmv (compared with its present value of around 1.7 ppmv). Methane is generated in signihcant amounts by the anaerobic decomposition of organic matter in modem marine sediments, but is oxidised by sulfate under the ocean sea floor and never reaches the atmosphere. Prior to the watershed constituted by the appearance of oxygenic photosynthesis, the ocean had little sulfate to support anaerobic oxidation of methane, but as atmospheric oxygen and seawater sulfate levels rose, the consequent anaerobic oxidation of methane would have steadily reduced the net release of methane. 

---