Deep-sea floor

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... 

Sedimentation rates range from centimeters per year in coastal sediments down to millimeters per thousand years on the deep-sea floor. Thus, the effects of molecular diffusion are generally greater than that of advection in shaping pore-water concentration profiles. 

Technically, whale falls represent another exemption caused by the rapid delivery of a large amount of POM to the deep-sea floor that can sustain a prolific benthic community for a significant period of... 

Clathrate hydrates Solid cages of water that form around small gas molecules such as methane, hydrogen, or carbon dioxide under conditions of high pressure and low temperature such as found on the deep sea floor and within the sediments. 

Hamilton (1959) has shown that a 150-700 meter-thick layer of unconsolidated sediments exists even on most deep sea floors. Let us consider a little more closely then the difference between the "open" sea situation, where sedimentary clays are in contact with sea water of roughly constant composition and an unconsolidated sediment which contains a pore fluid. 

The geological environments for these assemblages are those of weather ing, deep-sea floor sediments and continental shelf sediments, or shallow burial of these materials as sedimentary or tuffaceous rocks. 

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. 

Bender M.L. and Heggie D.T. (1984) Fate of organic carbon reaching the deep sea floor a status report. Geochim. Cosmochim. Acta 48, 977-986. 

Rowe, G.T., Boland, G.S., Phoel, W.C., Anderson, R.F., and Biscayne, PE. (1992) Deep-sea floor respiration as an indication of lateral input of biogenic detritus from continental margins. Cont. Shelf Res. 24, 132-139. 

Keywords Coasts Shelf Continental slope Continental footstep Underwater canyons Deep-sea floor Bottom sediments... 

The main components of marine sediments are inorganic aluminosilicate minerals which are usually accumulated on the sea floor by river and other geological activities, and also skeletons and shells of marine organisms (mainly calcium carbonate and silica) [2]. Of course, some metal salts or particulates which precipitate from seawater form new minerals, e.g. manganese nodules [2]. The chemical compositions of the three principal types of sediments in the ocean are shown in Table 12 [105], Most of the sediments found in the deep-sea floor are mixtures of these three principal minerals. Study of the sediments in the oceans and seashores can provide important data related to geochemical, oceanographical or biological circulation and deposition of elements, formation and distribution of marine sediments, and exploitation of marine resources. 

Gage, I. D. Tyler, P. A. (1991). Deep-Sea Biology A Natural History of Organisms on the Deep Sea Floor. Cambridge Cambridge University Press. 

Cryptococcus surugaensis sp. nov., a novel yeast species from sediments collected on the deep-sea floor of Suruga Bay. International Journal of Systematic and Evolutionary Microbiology, 53, 2095-8. 

Archer D., Emerson S., and Smith C. R. (1989b) Direct measurement of the diffusive sublayer at the deep sea floor using oxygen microelectrodes. Nature 340, 623-626. 

Jahnke R. A., Craven D. B., and Gaillard J.-F. (1994) The influence of organic matter diagenesis on CaC03 dissolution at the deep-sea floor. Geochim. Cosmochim. Acta 58, 2799-2809. 

The stability relationships between calcite, dolomite and magnesite depend on the temperature and activity ratio of Mg " /Ca " (Fig. 5d). Lower Mg/Ca activity ratios are required to induce the dolomitization of calcite and to stabilize magnesite at the expense of dolomite (Fig. 5d) (Usdowski, 1994). Formation waters from the Norwegian North Sea reservoirs have an average log(an g -/ cz- ) - TO to 0.0 and thus fall within the stability field of dolomite. Nevertheless, both calcite and dolomite are common cements in these rocks, indicating that dolomitization is a kinetically controlled reaction. Further evidence of this is revealed from Recent sediments, such as the Fraser River delta in Canada (Simpson Hutcheon, 1995) (log (aMg2+/aca=+) -2.2 to h-1.0), where the pore waters are saturated with respect to dolomite, but it is calcite rather than dolomite that precipitates. Calcite rather than dolomite forms below the deep>-sea floor, yet the pore waters plot at shallow, near sea bottom temperatures in the stability field of dolomite and shift with an increase in depth towards the stability field of calcite (Fig. 5d). This shift is due to a diffusion-controlled, downhole decrease in Mg/Ca activity ratio caused by the incorporation of Mg in Mg-silicate that results from the alteration of volcanic material, a process which is coupled with the release of calcium (McDuff Gieskes, 1976). 

Gage, J.D. and Tyler, P.A. (1991) Deep-sea biology a natural history of organisms at the deep-sea floor, Cambridge University Press, Cambridge. 

Lampitt, R.S. (1985) Evidence for the seasonal deposition of detritus to the deep-sea floor and its subsequent resuspension. Deep-Sea Research, 32, 885-897. 

Tunnicliffe, V., Juniper, S.K. and Sibuet, M. (2003) Reducing environments of die deep-sea floor, in Ecosystems of the World Ecosystems of the Deep Oceans (ed. P.A. Tyler), Chapter 4. 

Wyoming Elba Scotland Iceland Rare Oregon Western U.S., deep sea floor... 

Table 1.5 Relative areas of world oceans covered with pelagic sediments area of deep-sea floor = 268.1-10 km (from Berger (1976)).

Fig, 1.14 Distribution of dominant sediment types on the present-day deep-sea floor. The main sediment types are deep-sea clay and calcareous oozes which patterns are predominately depth-controlled, (from Davies and Gorsline (1976)). 

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