PHASE PHENOMENA IN CALCITE-SEAWATER SYSTEM 



197 



2300 



2288 



g 2276 



"to 



o 

 o 



| 2264 



o 

 t_ 

 u 



E 



2252 



2240 



200 400 



PRESSURE, atm 



600 



Fig. 5 Dissolution behavior in Sargasso Sea water. 



relating pressure to concentration (or total C0 2 ). The pressure at which this line 

 intersects the background total CO2 line is called the lysocline pressure for the 

 particular system. 



Figure 6 shows the results of the same experiment using artificial seawater of 

 33.5% salinity, a pH of 8.136, and a total C0 2 of 2.289 millimoles/liter. The 

 lysocline pressure is somewhat less, although the intersection has been shifted to 

 the right by the higher total CO2 . Real comparisons between experiments 

 require very similar values of the total C0 2 for establishing the lysocline 

 pressure. 



Figure 7 shows the results of the same experiment using Sargasso Sea water 

 diluted 1 : 1 with distilled water. The 18.7% salinity mixture was equilibrated 

 with air at 770 torrs and 23°C before use. Because the range of standards did not 

 extend low enough to include the total C0 2 of this seawater, the ordinate is 

 expressed in observed counts per second. Here the lysocline pressure has been 

 depressed to 2 38.7 atm, indicating that the aggressiveness of seawater in 

 dissolving calcium carbonate is dependent upon its salinity. This follows from 

 the expression of salinity as a measure of the calcium and magnesium 

 concentrations of the water. 



