Basins oceanic

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. 

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. 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. 

Besides the oceans, there are vast reserves of magnesium chloride in the Dead Sea Qaidam Basin, China and many salars of South America. 

Most commercial marine diatomite deposits exploit accumulations resulting from large blooms of diatoms that occurred ia the oceans during the Miocene geological epoch. Diatomite sediments older than the Jurassic period are rare in the fossil record. Commercial deposits of diatomite are accumulations of the fossil skeletons, which can occur in beds as thick as 900 m in some locations (5). Marine deposits must have been formed on the bottom of protected basins or other bodies of quiet water, undisturbed by strong currents, in an environment similar to the existing Santa Barbara Channel or Gulf of California (3,6). 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

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. 

Taylor and Marsh (7) investigated the long-term characteristics of temperature inversions and mixed layers in the lower atmosphere to produce an inversion climatology for the Los Angeles basin. In this area the cooler ocean currents produce an elevated inversion that is nearly always present and traps the pollutants released over the area within a layer seldom deeper than 1200 m and frequently much shallower. 

Over the past decade, plastic debris has become a common feature of beaches and coastal waters adjoining populated areas of Europe (36-38), the Mediterranean (39-41), North and Central America (42-44) and New Zealand (45). Plastics are also present in the open ocean both near the major shipping lanes and in the most remote regions of the world (the Arctic (46), the Benguela Current (47), the Cape Basin area of the South Atlantic (48), the Humboldt Current in the South Pacific (49), and the Antarctic (50, 51). 

In the Cape Basin region of the South Atlantic, polyethylene and polypropylene pellets were observed at concentrations of 1333-3600 pellets km (48). Since this area is far from any major shipping lane and is dominated oceanographically by the Antarctic West-Wind Drift with possibly some input from the Brazil Current, the source of the floating plastic was thought to be ships transporting the raw material in the South Atlantic (48). The weathered appearance of the pellets indicated that they had been adrift for an extended period and, therefore, carried long distances by the ocean currents. 

Rivers transport suspended sediments derived from the disintegration of basin surface layers. With reduced velocity, sediment is deposited in the river channel. The finest material is carried to the sea. It has been estimated that the average mechanical denudation rate for continents is 0.056 mm year (35). This is based on a total suspended load of 13.5 x 10 metric tons year (S). Presently, about two-thirds of the world s total suspended sediment load derives from Southern Asia and large Pacific Islands. Berner has estimated the increase in sediment loss in the U.S. and world since prehuman times to be approximately 200% (35). Current estimated erosion rate from the major land forms is provided in Table I. The relatively recent construction of large sediment trapping dams that normally caused sediment to be deposited in river valleys or transported to the ocean has drastically reduced sediment yields in great rivers. 

The synthesis of 1 kg of dry plant biomass requires the evapotranspiration of about 300 L of water, although smaller amounts of water are needed by some plants such as desert cacti. Approximately one-third of the annual continental rainfall (100 cm/yr) is returned to the atmosphere by evapotranspiration. Although it accounts for only about 10-15% of global evaporation, plant evapotranspiration can play a major role in local climates. For example, a molecule of water falling on the upper Amazon Basin is recycled on average five times during its eventual return to the Atlantic Ocean. 

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. 

Fig. 11-16 Partial pressure of CO2 in surface ocean water along the GEOSECS tracks (a) the Atlantic western basin data obtained between August 1972 and January 1973 (b) the central Pacific data along the 180° meridian from October 1973 to February 1974. The dashed line shows atmospheric CO2 for comparison. The equatorial areas of both oceans release CO2 to the atmosphere, whereas the northern North Atlantic is a strong sink for CO2. (Modified with permission from W. S. Broecker et al. (1979). Fate of fossil fuel carbon dioxide and the global carbon budget, Science 206,409 18, AAAS.)...

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... 

Kennett, J. P. and Ingram, B. L. (1995). A 20,000-year record of ocean circulation and climate change from the Santa Barbara Basin. Nature 377, 510-514. 

Cyperus rotundus L. is a weedy species, native to India, but widely distributed in countries on the Pacific Rim and islands in the Pacific Basin. Commonly referred to as purple nut sedge, it has been known in the Hawaiian Islands since the middle of the nineteenth century. In addition to its weedy nature, the taxon has attracted attention because of the antifebrile activity of its rhizomes. Chemical studies have disclosed the presence of several sesquiterpene derivatives, some of which have been implicated in the plant s medicinal use (cyperene and cyperinerol) (Wagner et ah, 1990, p. 1399). Our interest in this species is the existence of several chemotypes with interesting patterns of occurrence involving Pacific Rim countries and several oceanic islands, including the Hawaiian Islands, islands in the southern Pacific, and the Philippines. 

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