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ate alkalinity). Describe what properties you would measure and how you would use the data you
obtained to descriminate between these mechanisms.
3. How does calcite solubility vary with temperature and pressure in the ocean? Assume that tempera-
ture can be represented by a simple function of pressure:
T = 24 e P/5 +1
where pressure is in MPa and temperature in �C. Make a plot of the solubility product as a function of
depth between 0 and 5000 m using the equations in Examples 15.2 and 15.3. (Hint: remember to use
thermodynamic temperature).
Chemical Data from the North Pacific
4. Composition of seawater
Depth Salinity Cu N i Al
(a.) Calculate the molar concentrations of the major
0 0.54 2.49 90
ions in seawater listed in Table 15.2.
75 33.98 0.69 2.9 88
(b.) Calculate the ionic strength of this solution.
185 33.92 0.91 3.79 84
(c.) Using the equilibrium constants in Table 12.1,
375 34.05 1.45 5.26 70
calculate the concentration of carbonate ion in equi-
595 34 1.9 7.49 60
librium with this solution at 25�C.
780 34.19 2.15 9.07 52
(d.) Calculate the total alkalinity of this solution
985 34.37 2.38 9.64 48
assuming a pH of 8.1.
1505 34.55 2.8 9.79 45
5. Use the one-dimensional advection diffusion model
2025 34.61 3.18 10.6 47
in the depth interval of 595m to 4875 m and the
2570 34.65 3.46 10.8 50
chemical data from the North Pacific in the
3055 34.66 3.9 10.9 54
adjacent table to answer the following questions.
3533 34.66 4.26 10.7 63
For this locality, the ratio K was determined to be
4000 34.67 4.57 10.8 66
2300 and � to be 4. Is salinity conservative and the
4635 34.68 5.03 10.3 74
one-dimensional model applicable? Make a plot of
4875 34.68 5.34 10.4 79
S vs. �(z) (equation 15.33). Are Cu, Ni, and Al con-
Concentrations in nmol/kg; salinity in ppt.
servative? Are they being produced or scavenged?
For each of these elements, find a value of � or J to fit the one-dimensional advection-diffusion model
to the data.
6. Stanley and Byrne (1990) give the following stability constants for Zn complexes in seawater:
Zn2+ + Cl � ZnCl � * = 0.40
+
Zn2+ + HCO � ZnHCO � * = 0.83
3 3
700 January 25, 1998
W. M. W hit e Geochemistry
Chapter 15: Oceans
2
Zn2+ + CO � ZnCO3 � * = 2.87
3
2 2-
Zn2+ + 2CO � Zn(CO3) � * = 4.41
3 2
Zn2+ + H2O � Zn(OH)+ + H+ � * = -9.25
2
Zn2+ + SO � ZnCO4 � * = 0.90
4
Using these stability constants, a pH of 8.1, the ligand concentrations given in Table 15.2 (and the
equilibrium concentration of carbonate ion calculated with the equilibrium constant in Table 6.1 for a
temperature of 25�C), calculate the fraction of Zn present as each of these species plus free Zn2+.
7. Using the flows of water through mid-ocean ridge crest and flank hydrothermal systems and the
mass of the oceans given in Appendix I, how long does it take to cycle the entire ocean through these
systems?
8. In the San Clemente Basin, off the southern California coast, Barnes and Cochran (1990) found that
U concentrations in sediment pore waters decreased to 3.35 nM/l in the top 7 cm of sediment. Assuming
an effective diffusion coefficient (corrected for porosity and tortuosity in the sediment) of 68.1 cm2/yr,
calculate the flux (in nM/cm2) of U from seawater to sediment in this locality.
9. Using the fluxes of U to the ocean in Table 15.11, estimate the residence time of U in the ocean.
701 January 25, 1998
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