Sea floor

One method for measuring the temperature of the sea is to measure this ratio. Of course, if you were to do it now, you would take a thermometer and not a mass spectrometer. But how do you determine the temperature of the sea as it was 10,000 years ago The answer lies with tiny sea creatures called diatoms. These have shells made from calcium carbonate, itself derived from carbon dioxide in sea water. As the diatoms die, they fall to the sea floor and build a sediment of calcium carbonate. If a sample is taken from a layer of sediment 10,000 years old, the carbon dioxide can be released by addition of acid. If this carbon dioxide is put into a suitable mass spectrometer, the ratio of carbon isotopes can be measured accurately. From this value and the graph of solubilities of isotopic forms of carbon dioxide with temperature (Figure 46.5), a temperature can be extrapolated. This is the temperature of the sea during the time the diatoms were alive. To conduct such experiments in a significant manner, it is essential that the isotope abundance ratios be measured very accurately. 

Consumption of natural gas, as of the mid-1990s, was about 2000 x 10 /yr. Using seismic detection equipment, exploration firms search for gas reserves buried deep underground and beneath the sea floor. Advanced computer systems process the seismic data to pinpoint the most likely locations for reserves. These advanced systems have both cut the time required for data analysis, by 80%, and gready improved the success rate for new drill rigs. 

The flow of hydrothermal solutions iato the oceans from hydrothermal vents, ie, springs coming from the sea floor ia areas of active volcanism, and the chemical reactions occurring there by high temperature alteration of basalts ate of significance ia the mass balance of and. Eurthermore,... 

Since methane is almost always a byproduct of organic decay, it is not surprising that vast potential reserves of methane have been found trapped in ocean floor sediments. Methane forms continually by tiny bacteria breaking down the remains of sea life. In the early 197Qs it was discovered that this methane can dissolve under the enormous pressure and cold temperatures found at the ocean bottom. It becomes locked in a cage of water molecules to form a methane hydrate (methane weakly combined chemically with water). This "stored" methane is a resource often extending hundreds of meters down from the sea floor. 

Jack-up rigs. For drilling in water depths of up to 400 ft (122 m), the legs are cranked downward until they reach the sea floor and then jacked up so that the platform is 15 to 30 ft (4.6 m to 9.1 m) above the surface. Workers often reach the rig by helicopter (left). 

The structures used (platforms) require monitoring in addition to sub-sea pipelines, satellite wells and other equipment (e.g. manifolds) on the sea floor. Corrosion inhibitors are widely used in internal-streams (from the reservoir and many of the downstream operations). Corrosion monitoring can provide valuable data for assessing the effectiveness of the inhibitors used and for optimising dosage rates. 

Oceans occupy 70.8% or 125 million square miles of the surface of the earth. Within or beneath this inner space are foods, fuels, and minerals. Thus interest in the sea is obvious. At least 4/5 of all life on earth exists in saltwater. It is predicted that of the oil and gas demand in future years will come from oil at 2,000 ft. depths operated by manned submarines and marine robots. All the equipment needed to collect and store oil or gas will be installed and operated on the sea floor. Underwater housing and decompression chambers will be required. The sea bottom is also reported to include trillions of tons of copper, nickel, cobalt, iron, and other important minerals. 

From ships to submarines to mining the sea floor, certain plastics can survive sea environments, which are considered more hostile than those on earth or in space. For water-surface vehicles many different plastic products have been designed and used successfully in both fresh and the more hostile seawater. Figure 2-55 is an example where extensive use is made using unreinforced and reinforced plastics meeting structural and nonstructural product requirements. Included are compartments, electronic scanners, radomes, optically transparent devices, food storage and dispensing containers, medical products, buoyant devices, temperature insulators, and many more. 

POi that is incorporated into the authigenic apatite is thought to be supplied primarily via the decomposition of organic materials at the sea floor. A variety of additional processes, such as cycling at redox boundaries or incorporation by microbial communities, may act to elevate pore water concentrations, promoting... 

Nearly all of the detrital particles sinking into the deep ocean decompose and release the associated P. A small percentage (approximately 8%), however, do survive and accumulate on the sea floor. This P is then buried in the sediments (F i) and represents the ultimate removal of P from the ocean. 

Plate 4. The global sea floor topography from satellite altimetry and ship depth soundings, as described in Smith and Sandwell, 1997. (Kindly provided by Dr Walter Smith of NOAA.)... 

Urabe, T. and Sato, T. (1978) Kuroko deposits of the Kosaka mine. Northeast Honshu, Japan, Product of submarine hot-springs in Miocene sea floor. Econ. Geol, 73, 161-179. 

In 1990s, hydrothermal venting and mineralization were discovered on the sea floor of the back-arc basin, back-arc rift, and island arc surrounding the Japanese Islands as well as other western Pacific regions. 

Rubin KH, Macdougall JD, Perfit MR (1994) °Po- °Pb dating of recent volcanic eraptions on the sea floor. Nature 368 841-844... 

Kolodny Y, Kaplan IR (1970) Uranium isotopes in sea-floor phosphorites. Geochim Cosmochim Acta 34 3-24... 

Aller RC, DeMaster DJ (1984) Estimates of particle-flux and reworking at the deep-sea floor using Th-234/U-238 disequilibrinm. Earth Planet Sci Lett 67 308-318 Amid D, Cochran JK, Hirschberg DJ (2002) disequihbrium as an indicator of the seasonal... 

The materials so transported are deposited in a new environment, on land (terrestrial deposition), rivers (fluvial deposition), along coastal areas (marginal deposition) or on the sea floor (marine deposition). Dissolved components are deposited either by precipitation, or by evaporation or by the action of biological agencies. 

As a guide to the evolutionary history of the continents, Patterson decided to measure the lead isotope ratios of Earth s crust as a whole. As rocks erode, their minerals are collected and mixed in the oceans, where they eventually settle in layers of sediment. Patterson organized a formidable series of experiments to measure the lead isotopes on land, in various layers of ocean water, and in sediments on the sea floor. 

Figure 2.8 Reconstruction of a Middle Cambrian sea floor about 600,000,000 years ago. The fauna includes siliceous sponges (the upright cones), jellyfish, and two genera of trilobites (Paradoxides, the large form, and Eliipsocephalus, the small form). Bacteria had probably already been in existence for millions of years.

The interior zones - the core and the mantle - at high temperature interact very little with the surface, although here and there and now and then there is input to the surface from volcanoes and sea-floor black smokers . The surface also receives dust and debris from extra-terrestrial bodies and more rarely from more sizeable meteorites. 

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