Carbonate critical depth

Kolia et al. (1976) plotted the lysocline and the carbonate critical depth (Figure 4.20) using methods similar to those of Biscaye et al. (1976). Unfortunately, they did not use the 0 weight % intercept of the CCD which appears to be generally 100 to 400 m deeper than the carbonate critical depth. Also, their use of the term lysocline is not the same as the FL, because it is entirely based on the relation between water depth and carbonate content of the sediment, not... 

Figure 4.20. Carbonate lysocline and carbonate critical depth (CCrD) variations with latitude in the Indian Ocean. Data from Bengal and Arabian fans are excluded. (After Kolia et al., 1976.)...

The carbonate compensation depth (CCD) occurs where the rate of calcium carbonate dissolution is balanced by the rate of infall, and the calcium carbonate content of surface sediments is close to Owt.% (e.g., Bramlette, 1961). The CCD has been confused with the calcium carbonate critical depth (sometimes used interchangeably with the lysocline discussed next), where the carbonate content of the surface sediment drops below 10 wt.%. A similar marker level in deep-sea sediments is the ACD, below... 

E. L. Shock (1990) provides a different interpretation of these results he criticizes that the redox state of the reaction mixture was not checked in the Miller/Bada experiments. Shock also states that simple thermodynamic calculations show that the Miller/Bada theory does not stand up. To use terms like instability and decomposition is not correct when chemical compounds (here amino acids) are present in aqueous solution under extreme conditions and are aiming at a metastable equilibrium. Shock considers that oxidized and metastable carbon and nitrogen compounds are of greater importance in hydrothermal systems than are reduced compounds. In the interior of the Earth, CO2 and N2 are in stable redox equilibrium with substances such as amino acids and carboxylic acids, while reduced compounds such as CH4 and NH3 are not. The explanation lies in the oxidation state of the lithosphere. Shock considers the two mineral systems FMQ and PPM discussed above as particularly important for the system seawater/basalt rock. The FMQ system acts as a buffer in the oceanic crust. At depths of around 1.3 km, the PPM system probably becomes active, i.e., N2 and CO2 are the dominant species in stable equilibrium conditions at temperatures above 548 K. When the temperature of hydrothermal solutions falls (below about 548 K), they probably pass through a stability field in which CH4 and NII3 predominate. If kinetic factors block the achievement of equilibrium, metastable compounds such as alkanes, carboxylic acids, alkyl benzenes and amino acids are formed between 423 and 293 K. 

Quantification of changes in soil carbon dynamics, including SOM turnover rate and distribution of SOC with depth, is therefore critical for determining carbon storage in soils and for modeling soil carbon cycling. 

The LJ parameters, elk and a, have been determined from the critical constants, Tc and pc, by adopting the recommendation of Nicolas et al. [11] kTJe = 1.35 andpco3/e = 0.142. However, different values for the potential depth of benzene, 22, have been determined so as to fit the vapor pressure at temperatures from 307.2 K to 553.2 K. The LJ parameters used in this work are summarized in Table 1, where the parameters for graphitic carbon atom are taken from those suggested by Steele [10]. We used the modified Lorentz -Berthelot rule for the cross parameters, that is, the arithmetic mean for o and the geometric mean for e by introducing the binary parameter ktj defined as Eq. (4). 

The one key critical point that all of the iron-enrichment experiments have failed to show is an increase in the export of carbon to the deep sea. Even the Southern Ocean experiments, where a CO2 drawdown occurred, did not result in an increase in export flux. Sediment traps set out at a depth of... 

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