Seawater deep ocean

Ocean Basins. Known consohdated mineral deposits in the deep ocean basins are limited to high cobalt metalliferous oxide cmsts precipitated from seawater and hydrothermal deposits of sulfide minerals which are being formed in the vicinity of ocean plate boundaries. Technology for drilling at depth in the seabeds is not advanced, and most deposits identified have been sampled only within a few centimeters of the surface. 

Joly observed elevated "Ra activities in deep-sea sediments that he attributed to water column scavenging and removal processes. This hypothesis was later challenged with the hrst seawater °Th measurements (parent of "Ra), and these new results conhrmed that radium was instead actively migrating across the marine sediment-water interface. This seabed source stimulated much activity to use radium as a tracer for ocean circulation. Unfortunately, the utility of Ra as a deep ocean circulation tracer never came to full fruition as biological cycling has been repeatedly shown to have a strong and unpredictable effect on the vertical distribution of this isotope. 

Radium, like most other group II metals, is soluble in seawater. Formation of Ra and Ra by decay of Th in marine sediments leads to release of these nuclides from the sediment into the deep ocean. Lead, in contrast, is insoluble. It is found as a carbonate or dichloride species in seawater (Byrne 1981) and adheres to settling particles to be removed to the seafloor. 

Elderfield and Greaves [629] have described a method for the mass spectromet-ric isotope dilution analysis of rare earth elements in seawater. In this method, the rare earth elements are concentrated from seawater by coprecipitation with ferric hydroxide and separated from other elements and into groups for analysis by anion exchange [630-635] using mixed solvents. Results for synthetic mixtures and standards show that the method is accurate and precise to 1% and blanks are low (e.g., 1() 12 moles La and 10 14 moles Eu). The method has been applied to the determination of nine rare earth elements in a variety of oceanographic samples. Results for North Atlantic Ocean water below the mixed layer are (in 10 12 mol/kg) 13.0 La, 16.8 Ce, 12.8 Nd, 2.67 Sm, 0.644 Eu, 3.41 Gd, 4.78 Dy, 407 Er, and 3.55 Yb, with enrichment of rare earth elements in deep ocean water by a factor of 2 for the light rare earth elements, and a factor of 1.3 for the heavy rare earth elements. 

Bacon and Anderson [42] determined 230thorium and 228thorium concentrations, in both dissolved and particulate forms, in seawater samples from the eastern equatorial Pacific. The results indicate that the thorium isotopes in the deep ocean are continuously exchanged between seawater and particle surfaces. The estimated rate of exchange is fast compared with the removal rate of the particulate matter, suggesting that the particle surfaces are nearly in equilibrium with respect to the exchange of metals with seawater. 

The radiocarbon ratio also evolves very rapidly from its initial value of -50 to an average value of about -8 per mil. This evolution is not a consequence of evaporative concentration but, instead, of an approach to equilibrium with atmospheric carbon dioxide. Average surface seawater contains significantly less radiocarbon than does the atmosphere because its isotopic composition is affected by exchange with the deep ocean as... 

Because seawater is slightly compressible, the in-situ density of a parcel of seawater will increase as it is lowered into the deep ocean. As shown in Table 3-5, this effect is small, causing only a 4% increase if the seawater parcel is lowered from 0 to 4000 m (in the absence of any exchange of heat or salt with adjacent parcels). The hydrostatic... 

Many chemical reactions in seawater do not achieve equilibrium. The most notable are ones that involve marine organisms. Since organisms require energy, they cannot survive if their constituent biochemicals are at equilibrium. Equilibrium is also not likely to be achieved if some other process is adding or removing a chemical faster than equilibrium can be reattained. For example, calcium carbonate shells should spontaneously dissolve in deep ocean water, but some sink so fest that they can reach the sediments where they eventually become buried and, hence, preserved. In other words, the equilibrium approach is most applicable to reactions that attain equilibrium fester than any other competing processes acting on the chemical of interest. 

The oxidation munber of nitrogen in all organic compoimds is -III. Most of the dissolved nitrogen in seawater is in the form of DON except in the deep ocean where nitrate concentrations are very high. The mean smfece water DON concentration is 6 2 p,M N and in deep waters it is 4 2 p,M N. PON generally represents only a small fraction of the fixed nitrogen pool. 

Injection of compressed CO2 into the deep ocean has already been tested. The goal of this approach is to emplace the CO2 into waters with low temperatures, ensuring the formation of relatively immobile gas hydrates. This strategy has the potential to sequester thousands of gigatonnes of carbon, but likely environmental impacts include (1) a change in the pH in the seawater near the emplaced gas hydrates, (2) benthic kills, (3) other ecosystem impacts, and (4) release back to the atmosphere as an eventual consequence of meridional overturning circulation. 

The density of seawater varies from a maximum of c = 29, observed in deep antarctic waters, to a minimum of c = 25 in subtropical oceanic thermoclinal waters. The high density of polar waters causes them to sink beneath subtropical waters and constitutes the driving force of deep oceanic circulation. 

Hart R. (1970). Chemical exchange between seawater and deep ocean basalts. Earth. Planet. Sci. Letters., 9 269-279. 

Feasibility of Large-Scale CO2 Ocean Sequestration. This project, operated by the Monterey Bay Aquarium Research Institute will usea Remotely Operated Vehicle (ROV) to deploy small quantities of liquid CO2 in the deep ocean. Below about 10,000 feet the density of liquid CO2 exceeds that of seawater, and the liquid CO2 is quickly converted into a solid hydrate by reacting with the surrounding water. Using a Raman spectrometer, scientists will assess the impact that the CO2 hydrate material has on the ocean floor and ecosystem. 

Fabbricino, M., and Korshin, G. V. (2005). Formation of disinfection by-products and applicability of differential absorbance spectroscopy to monitor halogenation inchlorinated coastal and deep ocean seawater. Desalination 176, 57-69. 

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