Calcite depth profile

As in most parts of today s deep ocean the concentrations of Ca and of CO are nearly constant with water depth, profiles of CaCOs content with depth reflect mainly the increase in the solubility of the mineral calcite with pressure (see Figure 2). This increase occurs because the volume occupied by the Ca and ions... 

Saturation state of seawater, Cl, with respeot to (a) calcite and (b) aragonite as a function of depth. The dashed vertical line marks the saturation horizon. North Pacific profile is from 27.5°N 179.0°E (July 1993) and North Atlantio profile is from 24.5°N 66.0°W (August 1982) from CDIAC/WOCE database http //cdiac.esd.oml.gov/oceans/CDIACmap.html) Section P14N, Stn 70 and Section A05, Stn 84. Source From Zeebe, R.E. and D. Wolf-Gladrow (2001) Elsevier Oceanography Series, 65, Elsevier, p. 26. 

Initially, this Martian brine was equilibrated at Pco2 = 50 mbars within each of the ten layers. Under these conditions, virtually all the Fe (99.99%) precipitates as siderite (FeCOo), and 77.6 to 96.6% of the Ca precipitates as calcite (CaCOo) (Fig. 5.18). After equilibration of each 0.5-km layer separately, we then froze the profile from the top down, layer by layer, assuming that the freezing process would be sufficiently slow that all soluble salts would be ejected into the lower, unfrozen, layers. This process leads to increasing salt concentrations with depth (Fig. 5.18). These freezing simulations were done assuming that all Fe was removed in the initial evaporative concentration. Freeze concentration leads to the additional precipitation of calcite and... 

Typical vertical saturation profiles for the North Atlantic, North Pacific, and Central Indian oceans are presented in Figure 4.10. The profiles in the Atlantic and Indian oceans are similar in shape, but Indian Ocean waters at these GEOSECS sites are definitely more undersaturated than the Atlantic Ocean. The saturation profile in the Pacific Ocean is complex. The water column between 1 and 4 km depth is close to equilibrium with calcite. This finding is primarily the result of a broad oxygen minimum-C02 maximum in mid-water and makes choosing the saturation depth (SD) where Oc = 1 difficult (the saturation depth is also often referred to as the saturation level SL). 

Figure 8, A detailed profile of calcite and aragonite saturation states and sediment marker depth in the Northwestern Atlantic Ocean, (Percentages are estimates of the amount of calcite dissolution which must occur to produce a given marker level.)...

The carbon-14 age of calcite-rich deep sea sediments as a function of depth in the sediments at different locations in the ocean. Expedition names and core numbers are indicated along with the core location and water depth. Data (circles) indicate a 5—10 cm C mixed layer in the surface sediments everywhere in the deep ocean due to bioturbation by benthic fauna. The figure in the upper left illustrates the idealized relation between profile slope and sedimentation rate. Redrawn from Peng and Broecker (1984). 

The numerical model CoTReM was applied to investigate the depth dependent effects of respiration and redox processes related to CaCO dissolntion (Pfeifer et al. 2002 cf. Fig. 15.16 in chapter 15). Interestingly, if calculated until a steady-state situation is reached, the model-derived calcite dissolution and precipitation rates produce an almost perfect fit to the measured CaC03 profile in the sediment (Fig. 9.8), which suggests that 90 % of the CaC03 flux to the sea floor is redissolved in the sediment. 

Figure 3 Bathymetric profiles of calcium carbonate (calcite) saturation for hydrographic stations in the Atlantic and Pacific Oceans (data from Takahashi etai 1980). Carbonate saturation here is expressed as ACOa ", defined as the difference between the in situ carbonate ion concentration and the saturation carbonate ion concentration at each depth ACOa " = [C03 ]seawater - [COa Jsaturation)-The saturation horizon corresponds to the transition from waters oversaturated to waters undersaturated with respect to calcite (A 003 = 0). This level is deeper in the Atlantic than in the Pacific because Pacific waters are COa-enriched and [C03 ]-depleted as a result of thermohaline circulation patterns and their longer isolation from the surface. The Atlantic data are from GEOSECS Station 59 (30°12 S, 39°18 W) Pacific data come from GEOSECS Station 235 (16°45 N,161°23 W).

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