Trenches, deep-ocean

The Deep Sea Drilling Project (DSDP), currently the Integrated Ocean Drilling Program (IODP) of the National Science Foundation, has undertaken the most systematic evaluation of ocean hydrate deposits. The DSDP has recovered hydrate cores in the deep oceans from both coasts of the United States, from the Mid-America Trench off Guatemala, and off the coast of Peru. Atotal of 23 oceanic hydrate cores have been recovered, including the Gulf of Mexico and three Soviet... 

Other options that have been considered for HLW include outer space ejection and burial in deep ocean trenches. The consensus worldwide is that deep geological isolation is the best option. The United States leads in studying a specific site, Yucca Mountain. In other countries, even those generating a larger percentage of their power with nuclear power, the small volumes awaiting burial allow them more time to choose a location. 

There has been considerable interest in the possibility of disposing of industrial CO2 waste as hydrate in the deep ocean trenches. There have even been experiments con-... 

Disposal in deep oceanic trenches associated with subduction zones has also been proposed [25]. Subduction zones include areas of the earth along some continental margins... 

Other options that have been considered for HLW include outer space ejection and burial in deep ocean trenches. The consensus worldwide is that deep geological isolation is the best option. 

FIGURE 2.10 A schemaKc of ocean topography. The continental shelf, which may contain submarine canyons, extends from the shoreline to the deep ocean, abruptly ending at the continental slope. From the foot of the continental slope extends a more gentle continental rise. The deep ocean contains such features as trenches, active or extinct underwater volcanoes (seamounts and guyots), and mid-ocean ridges. 

You have been asked to prepare an outline design for the pressure hull of a deep-sea submersible vehicle capable of descending to the bottom of the Mariana Trench in the Pacific Ocean. The external pressure at this depth is approximately 100 MPa, and the design pressure is to be taken as 200 MPa. The pressure hull is to have the form of a thin-walled sphere with a specified radius r of 1 m and a uniform thickness t. The sphere can fail in one of two ways ... 

About 80% of the earth s surface is covered with aqueous solution. This liquid layer, the oceans, is called the hydrosphere. The average depth of the hydrosphere is about three miles but at ocean deeps or trenches, it changes precipitously to depths over twice that. 

The distribution of sediment types in the Pacific Ocean is much different from that of the Atlantic. Except for the coastline of the northwest United States, the Pacific is ringed by deep-sea trenches and, hence, has relatively narrow continental shelves. The trenches effectively trap all the terrigenous particles carried to the sea by river runoff. The Pacific Ocean is much wider than the other oceans thus the flux of wind-borne lithogenous particles is spread over a much greater area and produces a much lower mass flux, on an areal basis, to the seafloor. This makes other particles relatively important in determining the composition of the sediments in the Pacific ocean. 

There are several types of environments on Earth where significant water exists at prevalent low temperatures such that ice and liquid aqueous solutions commonly coexist permafrost, snow, glaciers, lake and river ice, sea ice, and parts of the atmosphere (polar troposphere, global upper troposphere, and stratosphere). In addition, the deep sea floor occurs at temperatures very close to the freezing point of water. For example, temperatures in the oceanic abysses hover around 2°C at a maximum hydrostatic pressure of 1100 bars (10,660 m) in the Mariana Trench (Yayanos, 1995). Table 4.1 summarizes some of these environments. Furthermore, in some permafrost and sea-floor environments, the presence of nonpolar gases under pressure can stabilize a modified form of ice known as gas hydrates even where temperatures are not quite low enough for ordinary ice to form. 

Trenches—The deep, trough-like depressions in the ocean floor that oceanic crust descends into when it is destroyed. 

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