:[
..c
a. Qi
0
CHAPTER 1 • The Carbonate System in Marine Environments
31
1.5
CaC0 3 Dissolution in Sea Water
The precipitation or formation of solid CaC03 in surface waters and the dissolution
of solid CaC0 3 in deep waters is very important in transferring CO2 from surface waters to deep waters. CaC03(s) is also present in pelagic sediments of the world oceans.
The saturation state of sea water with respect to CaC0 3 is determined from
where [Ci+] [CO~-] is the ion product of the concentration of Ca 2 + and CO~- and K;p
is the solubility product, at the "in situ" conditions, of S, t and P. Since Ca 2 + is a major
constituent of sea water (within 1%), its concentration can be estimated from the salinity. The solubility product for calcite formed by formanifera and aragonite formed
by pteropods can be determined from equations given in the appendix. The values of
[CO~-] can be determined from the measured carbonate parameters (pH and TA or
TA and Te0 2 ).
Values of Q for calcite and aragonite for Atlantic and Pacific waters are shown in
Fig. 1.19. The surface values of Q for calcite are near 5.0 and decrease below 1.0 in deep
water. The surface water value of Q is 3.0 for aragonite. Aragonite is 1.5 times more
soluble than calcite at a given t, P and salinity. The waters of the Pacific become undersaturated (Q< 1.0) at shallower depths than in the Atlantic. Approximate saturation levels in North Atlantic and North Pacific waters are given in Table 1.5.
The greater solubility of these minerals in deep waters is related to the effect of
pressure on the solubility of CaC03(s). Since two divalent ions are formed during the
dissolution, the volume change is large and negative due to electrostriction. The Pa0
2
0
1000
2000
3000
4000
5000
3
4
5
6
-0- Atlantic Ocean
.... Pacific Ocean
7
o
2
3
4
-0- Atlantic Ocean
..... Pacific Ocean
Fig. 1.19. The depth profile of the aragonite and calcite saturation state for the Atlantic and Pacific oceans
(Millero 1996)
5
..c
a. Qi
0
CHAPTER 1 • The Carbonate System in Marine Environments
31
1.5
CaC0 3 Dissolution in Sea Water
The precipitation or formation of solid CaC03 in surface waters and the dissolution
of solid CaC0 3 in deep waters is very important in transferring CO2 from surface waters to deep waters. CaC03(s) is also present in pelagic sediments of the world oceans.
The saturation state of sea water with respect to CaC0 3 is determined from
where [Ci+] [CO~-] is the ion product of the concentration of Ca 2 + and CO~- and K;p
is the solubility product, at the "in situ" conditions, of S, t and P. Since Ca 2 + is a major
constituent of sea water (within 1%), its concentration can be estimated from the salinity. The solubility product for calcite formed by formanifera and aragonite formed
by pteropods can be determined from equations given in the appendix. The values of
[CO~-] can be determined from the measured carbonate parameters (pH and TA or
TA and Te0 2 ).
Values of Q for calcite and aragonite for Atlantic and Pacific waters are shown in
Fig. 1.19. The surface values of Q for calcite are near 5.0 and decrease below 1.0 in deep
water. The surface water value of Q is 3.0 for aragonite. Aragonite is 1.5 times more
soluble than calcite at a given t, P and salinity. The waters of the Pacific become undersaturated (Q< 1.0) at shallower depths than in the Atlantic. Approximate saturation levels in North Atlantic and North Pacific waters are given in Table 1.5.
The greater solubility of these minerals in deep waters is related to the effect of
pressure on the solubility of CaC03(s). Since two divalent ions are formed during the
dissolution, the volume change is large and negative due to electrostriction. The Pa0
2
0
1000
2000
3000
4000
5000
3
4
5
6
-0- Atlantic Ocean
.... Pacific Ocean
7
o
2
3
4
-0- Atlantic Ocean
..... Pacific Ocean
Fig. 1.19. The depth profile of the aragonite and calcite saturation state for the Atlantic and Pacific oceans
(Millero 1996)
5