Oceans basins

Deposits that can be recovered without having to use explosives or other primary energy sources to break up the material in place ate called unconsoHdated deposits. These may be found stratified or disseminated as sutficial or subsurface deposits on the continental shelf or in deep ocean basins. 

Ocean Basins. Ocean basins are primarily formed from oceanic basalts and maybe interspersed with continental remnants, ridges, seamounts, or volcanic islands rising from the depths. Average water depth is around 4000 m but the most significant mineralization is generally found at 5000 m for manganese nodules, 4000 m for biogenic oozes, and 3000 m for hydrothermal metalliferous sulfides. The area is poorly explored, however. 

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. 

The outer shell of the earth, consisting of the upper mantle and the crust (Figure I4. lO), is formed of a number of rigid plates. These plates are 20 in number and are shown in Figure 14.1 I. Of these, six or seven are major plates, as can be seen in the map. The edges of these plates define their boundaries and the arrows indicate the direction of their movement. These plates contain the continents, oceans and mountains. They almost float on the partially molten rock and metal of the mantle. The outer shell, known as the lithosphere, is about 70 to 1,50 km thick. It has already moved great distances below the etirth s surface, ever since the earth was formed and is believed to be in slow and continuous motion all the time. The plates slide on the molten mantle and move about lO to 100 mm a year in the direction shown by the arrows. The movement of plates is believed to be the cause of continental drifts, the formation of ocean basins and mountains and also the consequent earthquakes and volcanic eruptions. 

The movement of these plates can ies with it continents, ocean basins and mountains. Scientists believe that convection currents are generated as a result of great heat within the earth, as illustrated in Figure 14. lO. Below the crust, the hot rocks and metal in liquid form rise to the crust, cool and sink into the mantle causing a turbulence through heat convection. The hot rocks become hardened at the surface of the mantle and push the crust which is part of the hug plates that are afloat the mantle. This movement of plates can cause the following ... 

If the plates pull down, they would sink into the mantle and melt to form ocean basins. Some of the molten rock of these plates may travel to the earth s surface through the crevice so formed due to heat convection and cause a volcano. 

If the Earth were a smooth sphere with the land planed off to fill the ocean basins the earth would be uniformly covered by water to a depth of 2430 m. 

The area, volume and average depth of the ocean basins and some marginal seas are given in Table 10-1. The Pacific Ocean is the largest and contains more than one-half of the Earth s water. It also receives the least river water per area of the major oceans (Table 10-2). Paradoxically it is also the least salty (Table 10-3). The land area of the entire Earth is strongly skewed toward the northern hemisphere. 

Table 10-2 A breakdown of the water balance for the four main ocean basins (cm/yr ...

Recently, the ocean-basin distribution of marine biomass and productivity has been estimated by satellite remote sensing. Ocean color at different wavelengths is determined and used to estimate near-surface phytoplankton chlorophyll concentration. Production is then estimated from chlorophyll using either in situ calibration relationships or from empirical functional algorithms (e.g., Platt and Sathyendranth, 1988 Field et al., 1998). Such studies reveal a tremendous amount of temporal and spatial variability in ocean biological production. 

Evaporite deposition is a much more episodic process and thus difficult to quantify. Because seawater is significantly undersaturated with respect to common evaporitic minerals, like gypsum and halite, evaporites are only formed when restricted circulation develops in an ocean basin in which evaporation exceeds precipitation. A geologically recent example is the Mediterranean Sea of 5-6 Myr ago. At this time excess evaporation exceeded the supply of ocean water through shallow inlet(s) from the Atlantic Ocean. As salinity increased, first CaS04, then NaCl precipitated. Over time, salt deposits 2-3 km thick formed. This thickness represents about 40 desiccations of the entire... 

Sturm ME, Goldstein SJ, Klein EM, Karson JA, Mnrrell MT (2000) Uranium-series age constraints on lavas from the axial valley of the Mid-Atlantic Ridge, MARK area. Earth Planet Sci Lett 181 61-70 Sun S, McDonongh WF (1989) Chemical and isotopic systematics of ocean basalts implications for mantle composition and processes. In Magmatism in the Ocean Basins. Saunders AD, Norry MJ (eds) Blackwell Scientific Pnbl. Oxford, p 313-345... 

Sun SS, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts implications for mantle composition and processes. In Magmatism in ocean basins. Saunders AD, Norry MJ (eds) Geol Soc Lond Spec Publ 42 313-345... 

Understanding the behavior of radionuclides in estuaries, as the dynamic interface between the continental hydrochemical systems and the ocean basins, requires consideration of broader chemical cycling in the hydrosphere. In this volume, the behavior of U- and Th-series isotopes in rivers is discussed by Chabaux et al. (2003), that in groundwaters by Porcelli and Swarzenski (2003), and that in oceans by Cochran and Masque (2003). General background information is provided by Bourdon et al. (2003). 

A survey of available Th data for the ocean basins demonstrated that the highest concentrations are found nearer to the coasts, and it was concluded that while eolian inputs likely dominated the budget in the open ocean and could account for increases near the coast, fluvial inputs may be more important in coastal regions. This implies that some a mechanism causes recycling of Th that has been removed to estuarine sediments (Huh et al. 1989). A study of an ice-covered region of the western Arctic Ocean found that significant amounts of °Th and Th were advected into the basin (Edmonds et al. 1998). Therefore, it appears that while long-lived Th isotopes are rapidly removed into estuarine sediments, transport into the ocean basins may continue. 

The redox properties of these systems are vitally important for possible abiotic chemical syntheses the main minerals present in young basalt ocean basins, at depths between 300 and 1,300 m, are pyrite (FeS2), pyrrhotite (FeS) and magnetite (Fe3C>4) (the PPM system). 

I apply these computational methods to various aspects of the Earth system, including the responses of ocean and atmosphere to the combustion of fossil fuels, the influence of biological activity on the variation of seawater composition between ocean basins, the oxidation-reduction balance of the deep sea, perturbations of the climate system and their effect on surface temperatures, carbon isotopes and the influence of fossil fuel combustion, the effect of evaporation on the composition of seawater, and diagenesis in carbonate sediments. These applications have not been fully developed as research studies rather, they are presented as potentially interesting applications of the computational methods. 

Metallic taste, 11 565 Metallic tungsten, 25 374 Metallic Type II superconductors, critical current density value in, 23 822 Metallic vanadates, 25 513 Metalliding, 15 251 Metalliferous oxides deposits of, 17 689-690 in ocean basins, 17 693 Metalliferous sulfide deposits, 17 690-691 Metalliferous sulfides, in ocean basins, 17 693-694... 

A system, which can be thought of as a lake, an ocean basin, a domain of the mantle or of the crust,. .. has a constant volume V in m3 (Figure 7.1). It receives an input Q of material (water, magma, sediments,. ..) in m3 a 1 and releases an equivalent output. Assuming that the system is well-stirred, C represents volumic concentrations in molm-3 of a conservative chemical species i. By conservative, it is meant (see... 

Two oceanic basins noted A and B contain initially a mass of sodium MA° and Mb°. Sodium residence time in each basin is rA and rB. Sodium exchange takes place... 

Figure 20. Calculated Fe isotope composition of seawater from different ocean basins based on a simple two-component mixing between Fe from aerosol particles and Fe from mid-oceanic-ridge (MOR) hydrothermal solutions. Atmospheric Fe fluxes (Jatm) for different ocean basins from Duce and Tindale (1991) MOR hydrothermal Fe flux ( mor) to different ocean basins were proportioned relative to ridge-axis length. Modified from Beard et al. (2003a).

The uniform isotopic composition of dissolved Mo in the oceans is readily understood in terms of the 10 -10 year Mo ocean residence time. For example, given an ocean mixing time of 10 years, and assuming that the 5 Mo contrast of different Mo isotope sources is <5%o (consistent with the range of values measured to date). Mo isotope variations between ocean basins or with depth should be <5%o/(10V10 ) = 0.05%o. Such variations are smaller than present analytical uncertainties. 

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