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About 30-40% of the carbon dioxide released by humans into the atmosphere dissolves into the oceans, rivers and lakes ^[1]^[2]. To maintain chemical equilibrium, some of it reacts with the water to form carbonic acid. Some of these extra carbonic acid molecules split up to give a carbonate ion and two hydrogen ions, thus increasing the ocean’s "acidity" (H⁺ ion concentration). This increasing acidity is thought to have a range of direct undesirable consequences such as depressing metabolic rates in jumbo squid^[3] and depressing the immune responses of blue mussels^[4]. (These chemical reactions also happen in the atmosphere, and as about 20% of anthropogenic CO₂ emissions are absorbed by the terrestrial biosphere^[2], also in the ground soils between absorbed CO₂ and soil moisture. Thus anthropogenic CO₂ emissions to the atmosphere can increase the acidity of land, sea and air.)

Other chemical reactions are also triggered which result in an actual net decrease in the amount of carbonate ions available. In the oceans, this makes it more difficult for marine calcifying organisms, such as coral and some plankton, to form biogenic calcium carbonate, and existing such structures become vulnerable to dissolution^[5]. Thus, ongoing acidification of the oceans also poses a threat to the food chains connected with the oceans.

Acidification

Dissolving CO
₂ in seawater increases the hydrogen ion (H⁺
) concentration in the ocean, and thus decreases ocean pH, by the following chemical reactions:

CO
_2(aq) + H
₂O ⇌ H
₂CO
₃

H
₂CO
₃ ⇌ H⁺ + HCO₃⁻

HCO₃⁻ ⇌ H⁺ + CO₃²⁻.

Bjerrum plot

is a graph of concentrations (or ratios of concentrations) of

Example

Chemical and mathematical derivation

Suppose that the interactions of carbon dioxide, hydrogen ions, bicarbonate and carbonate ions, all dissolved in water, are as follows:

CO
₂ + H
₂O ⇌ H⁺ + HCO₃⁻ (1)

HCO₃⁻ ⇌ H⁺ + CO₃²⁻. (2)

(Note that reaction (1) is actually a combination of two elementary reactions: CO
₂ + H
₂O ⇌ H
₂CO
₃ ⇌ H⁺ + HCO₃⁻.)

Assuming the mass action law applies to these two reactions, that water is abundant, and that the different chemical species are always well-mixed, their rate equations are:

{\frac {{\textrm {d}}[{\textrm {CO}}_{2}]}{{\textrm {d}}t}}=-k_{1}[{\textrm {CO}}_{2}]+k_{-1}[{\textrm {H}}^{+}][{\textrm {HCO}}_{3}^{-}],

{\frac {{\textrm {d}}[{\textrm {H}}^{+}]}{{\textrm {d}}t}}=k_{1}[{\textrm {CO}}_{2}]-k_{-1}[{\textrm {H}}^{+}][{\textrm {HCO}}_{3}^{-}]+k_{2}[{\textrm {HCO}}_{3}^{-}]-k_{-2}[{\textrm {H}}^{+}][{\textrm {CO}}_{3}^{2-}],

{\frac {{\textrm {d}}[{\textrm {HCO}}_{3}^{-}]}{{\textrm {d}}t}}=k_{1}[{\textrm {CO}}_{2}]-k_{-1}[{\textrm {H}}^{+}][{\textrm {HCO}}_{3}^{-}]-k_{2}[{\textrm {HCO}}_{3}^{-}]+k_{-2}[{\textrm {H}}^{+}][{\textrm {CO}}_{3}^{2-}],

{\frac {{\textrm {d}}[{\textrm {CO}}_{3}^{2-}]}{{\textrm {d}}t}}=k_{2}[{\textrm {HCO}}_{3}^{-}]-k_{-2}[{\textrm {H}}^{+}][{\textrm {CO}}_{3}^{2-}],

where [ ] denotes concentration, t is time, and $k_{1}$ and $k_{-1}$ are appropriate proportionality constants for reaction (1), called respectively the forwards and reverse rate constants for this reaction. (Similarly $k_{2}$ and $k_{-2}$ for reaction (2).)

At any equilibrium, the concentrations are unchanging, hence the left hand sides of these equations are zero. Then, from the first and fourth of these four equations, the ratios of rate constants equal the ratios of equilibrium concentrations, and these ratios, called $K_{1}$ and $K_{2}$ , are the equilibrium constants for these two reactions, i.e.

K_{1}={\frac {k_{1}}{k_{-1}}}={\frac {[{\textrm {H}}^{+}]_{\textrm {eq}}[{\textrm {HCO}}_{3}^{-}]_{\textrm {eq}}}{[{\textrm {CO}}_{2}]_{\textrm {eq}}}},

(3)

K_{2}={\frac {k_{2}}{k_{-2}}}={\frac {[{\textrm {H}}^{+}]_{\textrm {eq}}[{\textrm {CO}}_{3}^{2-}]_{\textrm {eq}}}{[{\textrm {HCO}}_{3}^{-}]_{\textrm {eq}}}},

(4)

where the subscript 'eq' denotes that these are equilibrium concentrations.

Rearranging (3) gives

[{\textrm {HCO}}_{3}^{-}]_{\textrm {eq}}={\frac {K_{1}[{\textrm {CO}}_{2}]_{\textrm {eq}}}{[{\textrm {H}}^{+}]_{\textrm {eq}}}},

(5)

and rearranging (4), then substituting in (5), gives

[{\textrm {CO}}_{3}^{2-}]_{\textrm {eq}}={\frac {K_{2}[{\textrm {HCO}}_{3}^{-}]_{\textrm {eq}}}{[{\textrm {H}}^{+}]_{\textrm {eq}}}}={\frac {K_{1}K_{2}[{\textrm {CO}}_{2}]_{\textrm {eq}}}{[{\textrm {H}}^{+}]_{\textrm {eq}}^{2}}}.

(6)

The total CO
₂ in the system at all times is given by

{\textrm {Tot}}[{\textrm {CO}}_{2}]=[{\textrm {CO}}_{2}]+[{\textrm {HCO}}_{3}^{-}]+[{\textrm {CO}}_{3}^{2-}].

Substituting in

References

^ Millero, Frank J. (1995). "Thermodynamics of the carbon dioxide system in the oceans". Geochimica et Cosmochimica Acta. 59 (4): 661–677. {{cite journal}}: Cite has empty unknown parameter: |coauthors= (help)
^ ^a ^b Feely, R.A.; et al. (2004). "Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans". Science. 305(5682): 362-366. {{cite journal}}: Explicit use of et al. in: |first= (help); Unknown parameter |month= ignored (help)
^ Rosa, R. and Seibel, B. (2008). "Synergistic effects of climate-related variables suggest future physiological impairment in a top oceanic predator". P.N.A.S. 105(52): 20776-20780. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
^ Bibby, R.; et al. (2008). "Effects of ocean acidification on the immune response of the blue mussel Mytilus edulis". Aquatic Biology. 2: 67-74. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Explicit use of et al. in: |first= (help)
^ Cite error: The named reference orr05 was invoked but never defined (see the help page).

[millero95-1] Millero, Frank J. (1995). "Thermodynamics of the carbon dioxide system in the oceans". Geochimica et Cosmochimica Acta. 59 (4): 661–677. {{cite journal}}: Cite has empty unknown parameter: |coauthors= (help)

[Feely04-2] Feely, R.A.; et al. (2004). "Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans". Science. 305(5682): 362-366. {{cite journal}}: Explicit use of et al. in: |first= (help); Unknown parameter |month= ignored (help)

[3] Rosa, R. and Seibel, B. (2008). "Synergistic effects of climate-related variables suggest future physiological impairment in a top oceanic predator". P.N.A.S. 105(52): 20776-20780. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)

[4] Bibby, R.; et al. (2008). "Effects of ocean acidification on the immune response of the blue mussel Mytilus edulis". Aquatic Biology. 2: 67-74. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Explicit use of et al. in: |first= (help)

[orr05-5] Cite error: The named reference orr05 was invoked but never defined (see the help page).

[1]

[2]

[3]

[4]

[5]

@@ Line 26: / Line 26: @@
 ==Chemical and mathematical derivation==
-Suppose that [[carbon dioxide]], [[water]], [[hydron|hydrogen ions]], [[bicarbonate]] and [[carbonate]] [[ions]] interact through the following chemical reactions:
+Suppose that the interactions of [[carbon dioxide]], [[hydron|hydrogen ions]], [[bicarbonate]] and [[carbonate]] [[ions]], all dissolved in [[water]], are as follows:
-: {{chem|CO|2(aq)}} + {{chem|H|2|O}} {{eqm}} {{chem|H|2|CO|3}}
+: {{chem|CO|2}} + {{chem|H|2|O}} {{eqm}} H<sup>+</sup> + HCO<sub>3</sub><sup>−</sup> {{space}} {{space}} {{space}} {{space}} {{space}} {{space}} {{space}} (1)
-: {{chem|H|2|CO|3}} {{eqm}} H<sup>+</sup> + HCO<sub>3</sub><sup>−</sup>
+: {{space}} {{space}} {{space}} HCO<sub>3</sub><sup>−</sup> {{eqm}} H<sup>+</sup> + CO<sub>3</sub><sup>2−</sup>. {{space}} {{space}} {{space}} {{space}} {{space}} {{space}} {{space}} (2)
-: HCO<sub>3</sub><sup>−</sup> {{eqm}} H<sup>+</sup> + CO<sub>3</sub><sup>2−</sup>.
+(Note that reaction (1) is actually a combination of two [[elementary reaction]]s: {{chem|CO|2}} + {{chem|H|2|O}} {{eqm}} {{chem|H|2|CO|3}} {{eqm}} H<sup>+</sup> + HCO<sub>3</sub><sup>−</sup>.)
+Assuming the [[mass action law]] applies to these two reactions, that water is [[Abundance (chemistry)|abundant]], and that the different chemical species are always well-mixed, their [[rate equation]]s are:
+: <math>\frac{\textrm{d}[\textrm{CO}_2]}{\textrm{d}t}= -k_1[\textrm{CO}_2] + k_{-1}[\textrm{H}^+][\textrm{HCO}_3^-], </math>
+: <math>\frac{\textrm{d}[\textrm{H}^+]}{\textrm{d}t}= k_1[\textrm{CO}_2] - k_{-1}[\textrm{H}^+][\textrm{HCO}_3^-] + k_2[\textrm{HCO}_3^-] - k_{-2}[\textrm{H}^+][\textrm{CO}_3^{2-}], </math>
+: <math>\frac{\textrm{d}[\textrm{HCO}_3^-]}{\textrm{d}t}= k_1[\textrm{CO}_2] - k_{-1}[\textrm{H}^+][\textrm{HCO}_3^-] - k_2[\textrm{HCO}_3^-] + k_{-2}[\textrm{H}^+][\textrm{CO}_3^{2-}], </math>
+: <math>\frac{\textrm{d}[\textrm{CO}_3^{2-}]}{\textrm{d}t}= k_2[\textrm{HCO}_3^-] - k_{-2}[\textrm{H}^+][\textrm{CO}_3^{2-}], </math>
+where [{{space}}] denotes [[concentration]], ''t'' is time, and <math>k_1</math> and <math>k_{-1}</math> are appropriate [[Proportionality (mathematics)|proportionality]] constants for reaction (1), called respectively the forwards and reverse [[Reaction rate constant|rate constants]] for this reaction. (Similarly <math>k_2</math> and <math>k_{-2}</math> for reaction (2).)
+'''At any [[Chemical equilibrium|equilibrium]]''', the concentrations are unchanging, hence the left hand sides of these equations are zero. Then, from the first and fourth of these four equations, the ratios of rate constants equal the ratios of equilibrium concentrations, and these ratios, called <math>K_1</math> and <math>K_2</math>, are the [[equilibrium constant]]s for these two reactions, i.e.
+: <math> K_1 = \frac{k_1}{k_{-1}} = \frac{[\textrm{H}^+]_{\textrm{eq}}[\textrm{HCO}_3^-]_{\textrm{eq}}}{[\textrm{CO}_2]_{\textrm{eq}}}, </math> {{space}} {{space}} {{space}} {{space}} (3) {{space}} {{space}} {{space}} {{space}}
+: <math> K_2 = \frac{k_2}{k_{-2}} = \frac{[\textrm{H}^+]_{\textrm{eq}}[\textrm{CO}_3^{2-}]_{\textrm{eq}}}{[\textrm{HCO}_3^-]_{\textrm{eq}}}, </math> {{space}} {{space}} {{space}} {{space}} {{space}} (4)
+where the subscript 'eq' denotes that these are equilibrium concentrations.
+Rearranging (3) gives
+: <math> [\textrm{HCO}_3^-]_{\textrm{eq}} =  \frac{K_1[\textrm{CO}_2]_{\textrm{eq}}}{[\textrm{H}^+]_{\textrm{eq}}}, </math> {{space}} {{space}} {{space}} {{space}} (5)
+and rearranging (4), then substituting in (5), gives
+: <math> [\textrm{CO}_3^{2-}]_{\textrm{eq}} =  \frac{K_2[\textrm{HCO}_3^-]_{\textrm{eq}}}{[\textrm{H}^+]_{\textrm{eq}}}
+=  \frac{K_1K_2[\textrm{CO}_2]_{\textrm{eq}}}{[\textrm{H}^+]_{\textrm{eq}}^2}. </math> {{space}} {{space}} {{space}} {{space}} (6)
+{{space}}
+The total {{chem|CO|2}} in the system at all times is given by
+: <math> \textrm{Tot}[\textrm{CO}_2] =  [\textrm{CO}_2] + [\textrm{HCO}_3^-] + [\textrm{CO}_3^{2-}]. </math>
+Substituting in
 ==References==