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Chemical Oceanography, 4th Edition
This order is due to the increase in polarizability of the d 10 electrons in the metals and
the large halide ligands. The complexes thus have more covalent character. Since the concentration of Cl – in seawater is much larger than that of the other halides, the Cl – complexes
will normally dominate (the values of K MX for the heavier halides are not large enough to
compensate for the low concentration). It is possible, however, for OH – ions to compete successfully with Cl – . For Cl – complexes to predominate, the value of log K MCl – log K MOH must
be greater than about –5.4. The values of log K MCl and log K MOH for various metal ions are
shown in Table 3.4. From this table, it is evident that the strength of the Cl – complexes is
greater than for the OH – complexes for Ag + , Cd 2+ , Hg 2+ , and Zn 2+ but not for Cu 2+ and Pb 2+ .
The SO 4
2– ion cannot compete with Cl – and OH – ions for the formation of complexes with
the d 10 cations. The addition of higher concentrations of Cl – (e.g., brines) can contribute to
Table 3.1 (continued)
Speciation, Concentration, and Distribution Types of Elements in Ocean Waters
Element
Probable Species
Range and Average Concentration
Type of Distribution
Sb
Sb(OH) 6
–
1.2 nM
?
Te
TeO 3
2– , HTeO 3
–
?
?
I
IO 3
–
0.2–0.5 μM, 0.4 μM
Nutrient type
Cs
Cs +
2.2 nM
Conservative
Ba
Ba 2+
32–150 nM, 100 nM
Nutrient type
La
LaCO 3
+
13–37 pM, 30 pM
Surface depletion
Ce
CeCO 3
+
16–26 pM, 20 pM
Surface depletion
Pr
PrCO 3
+
4 pM
Surface depletion
Nd
NdCO 3
+
12–25 pM, 10 pM
Surface depletion
Sm
SmCO 3
+
3–5 pM, 4 pM
Surface depletion
Eu
EuCO 3
+
0.6–1 pM, 0.9 pM
Surface depletion
Gd
GdCO 3
+
3–7 pM, 6 pM
Surface depletion
Tb
TbCO 3
+
0.9 pM
Surface depletion
Dy
DyCO 3
+
5–6 pM, 6 pM
Surface depletion
Ho
HoCO 3
+
1.9 pM
Surface depletion
Er
ErCO 3
+
4–5 pM, 5 pM
Surface depletion
Tm
TmCO 3
+
0.8 pM
Surface depletion
Yb
YbCO 3
+
3–5 pM, 5 pM
Surface depletion
Lu
LuCO 3
+
0.9 pM
Surface depletion
Hf
Hf(OH) 4
<40 pM
?
Ta
Ta(OH) 5
<14 pM
?
W
WO 4
2–
0.5 nM
Conservative
Re
ReO 4
–
14–30 pM, 20 pM
Conservative
Os
?
?
?
Ir
?
0.01 pM
?
Pt
PtCl 4
2–
0.5 pM
?
Au
AuCl 2
–
0.1–0.2 pM
?
Hg
HgCl 4
2–
2–10 pM, 5 pM
?
Tl
Tl + , TCl
60 pM
Conservative
Pb
PbCO 3
5–175 pM, 10 pM
Surface input, depletion at depth
Bi
BiO + , Bi(OH) 2
+
<0.015–0.24 pM
Depletion at depth