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Processes in the Oceans
The extrapolated values to [Mg] = 0 can be used to estimate the concentrations at high
temperature. The concentrations of Ca 2+ and Sr 2+ coming from the vents are shown in
Figure 10.28 and Figure 10.29, respectively.
The extrapolated pH of the hydrothermal waters is close to 4.0 (see Figure 10.30). The SO 4
2–
ion shows a loss in the hydrothermal waters as expected (see Figure 10.31). The trace metals Mn 2+ , Fe 2+ , and Zn 2+ show increases as the Mg decreases (Figure 10.32 to Figure 10.34).
The measurements of Na + and Cl – versus Mg 2+ are not as conclusive (see Figure 10.35 and
Figure 10.36, respectively). The loss of Na + and Cl – may occur at the triple point of seawater
(~350°C, liquid and vapor are in equilibrium). A comparison of the estimated composition
Temperature (°C)
0
2
4
6
8
10
12
14
Si (µM)
200
400
600
800
Figure 10.22
Concentration of SiO 2 as a function of the temperature for the Galapagos vent waters.
Si (µM)
0
200
400
600
800
Mg (mM)
51.0
51.5
52.0
52.5
53.0
Figure 10.23
Concentration of magnesium as a function of the silica concentration.