Calcareous ooze

In spite of these limitations, estimates for ocean storage capacity in excess of 100,000 billion GtC have been cited (Herzog et al., 1997). Such numbers would only be feasible if alkalinity (i.e., NaOH) is added to the ocean to neutralize the corresponding amounts of carbonic acid formed. Over thousands of years, the dissolution of calcareous oozes at the bottom of the ocean could provide such alkalinity (Archer et al., 1997 Broecker and Takahashi, 1978). 

All of these measures of saturation are very useful in predicting the geographic distribution of sedimentary carbonates. For example, sediments lying below waters that are undersaturated with respect to calcite should be devoid of calcareous oozes. Since direct measurement of [COj ] observed difficult, its concentration is usually computed from two more easily measured parameters, the carbonate alkalinity and pH of a seawater sample. 

Based on thermodynamic considerations, sediments that lie at depths below the saturation horizon should have 0% CaCOj. This then explains why calcareous oozes are restricted to sediments lying on top of the mid-ocean ridges and rises and why the sediments of the North Pacific are nearly devoid of calcite and aragonite. (The low %CaCOj in the sediments of the continental margin is a result of dilution by terrestrial clay minerals.)... 

Once the PIC reaches the seafloor, it is still subject to dissolution if the bottom waters are undersaturated. Protection against postdepositional dissolution is provided by rapid burial. Calcareous oozes are created when burial is achieved by sedimenting particles that are predominantly PIC. 

The model provided in Figure 20.1 is for an ocean basin whose abyssal plains all lie below the CCD. This most closely resembles the conditions in the North Pacific, whereas the rest of the ocean basins have a significant portion of their abyssal plains lying above the CCD, and, hence, contain some calcareous oozes. From a global perspective, calcareous oozes are more abundant than siliceous oozes. This is caused by two phenomena (1) all seawater is undersaturated with respect to opal, whereas all surface waters and 20% of the deep waters are saturated with respect to calcite, and (2) siliceous plankton are dominant only in upwelling areas. 

As shown in Table 20.1, biogenous oozes are the most common type of pelagic oceanic sediment, with calcareous oozes dominating. 

In the South Pacific, the CCD is deep enough to permit the preservation of calcareous oozes except in the center of the basin, which as a result is covered by abyssal clays. The relatively rapid supply of hydrogenous sediments prevents the accumulation of calcareous oozes on the East Pacific Rise. In the North Pacific, abyssal clays dominate as this is the location where the CCD is shallowest. Aeolian transport is the source of the clay minerals that make up these deposits. 

Aside from Sr, the original biogenic components of calcareous oozes also contain variable and minor amounts of other elements, like Mg, Na and S, all of which affect the solubility of the biogenic phases. Magnesium is especially... 

Many chalks undergoing burial diagenesis in the present oceanic realm and those exposed on land were originally pelagic foram-nannofossil calcite oozes. However, calcareous oozes deposited in the periplatform environment are compositionally more complex. These oozes represent transitional carbonate deposits found between carbonate banks and the deep sea (Schlager and James,... 

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. 

Composition Red clay Calcareous ooze Siliceous ooze... 

Similar ponds of metalliferous sediment are observed close to other inactive sulfide stmctures throughout the TAG area (Rona et al., 1993). Metz et al. (1988) characterized the metalliferous sediment in a core raised from a sediment pond close to one such deposit, 2 km NNE of the active TAG mound. That core consisted of alternating dark red-brown layers of weathered sulfide debris and fighter calcareous ooze. Traces of pyrite, chalcopyrite, and sphalerite, together with elevated transition-metal concentrations were found in the dark red-brown layers. 

Biogenous oozes are either calcareous or siliceous. Calcareous oozes are predominantly the calcitic tests of coccolithophores and/or foraminifera, or the aragonitic tests of pteropods. The solubility of CaCOs increases with decreasing temperature and increasing pressure, and thus with increasing depth in the oceans. Aragonite is 1.45 times more soluble than calcite (Morse and Mackenzie, 1990), so aragonitic oozes are confined to shallower depths than the calcitic oozes. The compensation depth for each mineral is defined as the depth at which the rates of... 

Calcareous ooze and pelagic clays are the predominant deep-sea sediments in offshore regions... 

Table 1.5). The distribution of these sediments in the three great oceans shows a considerable degree of variation (Fig. 1.14). The distribution patterns strongly depend on the water depth, i.e. the position of the CCD. Calcareous ooze, primarily consisting of foraminiferal oozes and nanno-plankton oozes, covers vast stretches of the sea-... 

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)). 

Equation 2.1 describes the fractional porosity which ranges from 0 in case of none pore volume to 1 in case of a water sample. Multiplication with 100 gives the porosity in percent. Depending on the sediment type porosity occurs as inter- and intraporosity. Interporosity specifies the pore space between the sediment grains and is typical for terrigenous sediments. Intraporosity includes the voids within hollow sediment particles like foraminifera in calcareous ooze. In such sediments both inter- and intraporosity contribute to the total porosity. 

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