Deep-sea trenches

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. 

The level of compression of carbon dioxide required is dependent on the disposal option but can generally be said to be in the range of 150-180 bar for disposal in saline aquifers and depleted oil reservoirs. Disposal in coal measures may require less compression (80-100 bar) and deep sea trenches more (250-300 bar). High capacity carbon dioxide injection plants are complex and require multi-stage compression steps. This amount of compression requires significant levels of power, this has been estimated by Saxena and Flintoff and summarised in Table 6.6 for... 

Taylor S. R. (1977) Island arc models and the composition of the continental crust. In Island Arcs, Deep Sea Trenches, and Back-Arc Basins, Geophys. Monogr. 1 (eds. M. Taiwan and W. C. Pitman). American Gephysical Union, Washington, DC, pp. 325-335. 

For the foreseeable future, the vast majority of research for disposal applications is likely to be focused on understanding and mitigating environmental concerns that arise from disposal and is unlikely to be directed at reducing the cost of disposal (Freund and Ormerod, 1997). Freund and Ormerod (1997) cite estimates for transport and disposal cost that range from 4.7 to 21 per ton of CO2 depending upon whether the sequestration is to take place in a nearby depleted oil and gas well or a deep-sea trench that is located some distance from an onshore fossil-fueled power plant. In the absence of research that pairs current and future power plant sites with disposal sites on a global basis, we will assume an intermediate value of 55 per tonne of carbon ( 15 per tonne of CO2) for all transport and disposal costs and hold this cost constant throughout the time period under study. 

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 ... 

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... 

Boetius, A., S. Scheibe, A. Tselepides, and H. Thiel. 1996. Microbial biomass and activities in deep-sea sediments of the eastern Mediterranean Trenches are benthic hotspots. Deep-Sea Research 143 1439—1460. 

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. 

Kato, C. (1999). Molecular analyses of the sediment and isolation of extreme barophiles from the deepest Mariana Trench. In Extremophiles in Deep-sea Environments, ed. 

Richards, F. A., and Benson, B. B. (1960). Nitrogen/argon and nitrogen isotope ratios in two anaerobic environments, the Cariaco Trench in the Caribbean Sea and Dramsfjord, Norway. Deep-Sea Res. 7, 254-264. 

Fry B., Jannasch H. W., Molyneaux S. J., Wirsen C. O., Muramoto J. A., and King S. (1991) Stable isotope studies of the carbon, nitrogen and sulfur cycles in the Black Sea and the Cariaco Trench. Deep-Sea Res. 38, S1003-S1019. 

Jacobs L., Emerson S., and Huested S. S. (1987) Trace metal geochemistry in the Cariaco Trench. Deep-Sea Res. 34, 965-981. 

Foraminifera from the sediments of the Cariaco Trench (Fig. 7.6) (Hughen et al, 2004). Since the sediments of this anoxic basin are varved, the age filter applied to most sediment cores by bioturbation is not an issue. Calendar ages of the varves in the sediments of this basin were determined by matching the percent reflectance (a measure of the color of the sediments) with 5 0 variations in the ice of a Greenland ice core (described later in Fig. 7.19). Since the latter record is precisely dated back to 40 000 years by actual counting of annual ice layers, and the two records are undeniably correlated, it was possible to determine an accurate calendar age for the Cariaco Trench sediment core by using variations in the percent reflectance record. The results in Fig. 7.6 indicate offsets of up to 5 ky between C age and calendar age at about 30 ky BP and an abrupt shift at 40 calendar kiloyears (cal. ky) BP in which 7000 C years elapsed in only 2000 y. The results have been explained as variations in the source function and the ventilation of the deep sea and are now used to correct C dates back to more than 40 cal. ky BP. 

Lundberg, N. and Casey Moore, J. 1982. Structural features of the Middle America Trench slope off southern Mexico, Deep Sea Drilling Project Leg 66. In J.S. Watkins, J. Casey Moore et al. (Editors), Initial Reports of the Deep Sea Drilling Project, 66. US Government Printing Office, Washington DC, pp. 793-805. 

The continental slope is the "relatively steep (usually 3-6°) portion of the seafloor which lies at the seaward border of the continental shelf" (Heezen et al., 1959) in water depths ranging from 100-200 m to 1,400-3,200 m, and locally to much greater depths (Bouma, 1979). This area is located just above the transition between continental and oceanic crust. The continental slopes are narrow (20-100 km), covering an area approximately 2.87 X 10E6 km, 5.6% of the Earth s surface (Drake and Burke, 1974). About half of the world s continental slopes terminate in deep-water trenches or shallower depressions, the rest gradually merging with slopes of 1 100 to 1 700 into continental rises and their deep-sea fans (Curray, 1966). 

Piper, D.J.W. 1978. Turbidite muds and silts on deep sea fans and abyssal plains. In Sedimentation in Submarine Canyons, Fans, and Trenches, Stanley, D.J., and Kelling, G., eds., Dowden, Hutchinson... 

Maynard, J.B., R. Valloni and H.-S. Yu, 1982, Composition of Modern Deep-Sea Sands from Arc-related Basins, in Trench and Fore-arc Sedimentation, ed. J.K. Leggett (Geological Society of London, London) pp. 551-561. 

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