Abyssal zone

Most of the polychaetes and nematodes in the eutrophic abyssal zone belong to families considered to be deposit feeders (e.g. Kukert Smith,... 

The data in Table 2.11 show that more than 80% of the animal biomass occurs on the continental shelves, which represents less than 8% of the immersed surface area. The abyssal zone, which represents more than three-fourths of... 

Walker, D., Shibata, T. DeLong, S. E. (1979). Abyssal tholeiites from the Oceanographer Fracture Zone. Contrib. Mineral. Petrol., 70, 111-25. 

However, salinity values are easily obtained with a salinometer (which measures electrical conductivity and is appropriately calibrated with standard solutions and adjusted to account for T effects). The salinity of seawater increases if the loss of H2O (evaporation, formation of ice) exceeds the atmospheric input (rain plus rivers), and diminishes near deltas and lagoons. Salinity and temperature concur antithetically to define the density of seawater. The surface temperature of the sea reflects primarily the latitude and season of sampling. The vertical thermal profile defines three zones surface (10-100 m), where T is practically constant thermoclinal (100-1000 m), where T diminishes regularly with depth and abyssal... 

Figure 6.1 The major routes of sediment transport from land to the open ocean can simply be illustrated through the following sequence streams, rivers, estuaries, shallow coastal waters, canyons, and finally the abyssal ocean. Arrows indicate the effects of coastal currents and resuspension events on the transport and distribution of particles delivered to the coastal zone. There can be substantial storage in each of these environments. (From Degens, 1989, with permission.)...

The sediments of the abyssal plain of the central Black Sea region are mostly biogenic and are enriched with organic matter. The floor of the deepwater depression is covered with coccolith oozes. In peripheral zones, in addition, terrigenous lowly calcareous oozes and carbonate-free silts are observed. 

Marine sediments cover the ocean floor to a thickness averaging 500 m. The deposition rates vary with topography. The rate may be several millimetres per year in nearshore shelf regions, but is only from 0.2 to 7.5 mm per 1000 years on the abyssal plains. Oceanic crustal material is formed along spreading ridges and moves outwards eventually to be lost in subduction zones, the major trenches in the ocean. Because of this continual movement, the sediments on the seafloor are no older than Jurassic in age, about 166 million years. 

Modern oceanic mantle is defined solely by abyssal peridotites, which are samples of harzbur-gite and Iherzolite collected from fracture zones at oceanic spreading centers, and these samples are representative of shallow oceanic lithosphere that has been processed at mid-ocean ridges (see Chapter 2.04). Two types of continental mantle lithosphere are considered (i) cratonic mantle, which refers to xenoliths collected from kimberlites that sample portions of mantle beneath stable, Archean cratons and (ii) off-craton mantle, which refers to xenoliths collected from alkalic basalts that have sampled portions of the subcontinental mantle adjacent to ancient cratonic mantle (see Chapter 2.05). Also included with off-craton lithosphere are orogenic Iherzolites and ophiolites, which are slices of mantle tectonically emplaced typically at convergent margins. 

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