Ocean Acidification: The Other CO2 Problem
Figures
Scott C. Doney,1 Victoria J. Fabry,2 Richard A. Feely,3 and Joan A. Kleypas4
Q. Why is surface ocean
PCO2 < atmospheric PCO2?
Q.pH measured
or calculated?
Q. What is GEOSECS?
Q. Why is Ω calcite > Ωaragonite?
Q. Why is Ω > 1?
Q. What would pH be for Ω = 1.0?
Annual Reviews
Fig. 1. (A) Atmospheric CO2 emission scenario and concentrations based on the Los Alamos National
Laboratory general circulation model after Caldeira and Wickett (4)
R. A. Feely et al., Science 305, 362 -366 (2004)
Published by AAAS
Meridional Sections of C*
Q. Where is calcite line?
Q. Why shoaled?
Q. Why in North Pacific?
Q. How is this C* calculated?
Doney et al (2009) Annual Reviews
also
Sabine et al (2004)
Anthropogenic CO2 = DC*
See Gruber (1998) GBC, 12, 165-191
DC* = Cmeas – Ceq (S, T, Alk° ) – r C:O2 (O2 – O2sat) – ½ (Alk - Alk° + r N:O2 (O2-O2sat)
Ceq = DIC for PCO2 = 280 matm
Alk° = preformed alkalinity
Approach:
Take measured DIC (Cmeas).
Subtract preformed value (amount water had when it sank)
Subtract how much DIC has been added by respiration using O2 – O2sat.
Subtract how much DIC has been added by CaCO3 dissolution using the change
in alkalinity. Correct for alkalinity due to NO3 production.
Used to separate anthropogenic CO2 from the large variable background carbon ©
Fig. 4. Maps of anthropogenic CO2 on the (A) 26.0 and (B) 27.3 potential density surfaces
26.0 is at about 200m
27.3 is at about 1000m
C. L. Sabine et al., Science 305, 367 -371 (2004)
Published by AAAS
Fig. 1. Column inventory of anthropogenic CO2 in the ocean (mol m-2)
C. L. Sabine et al., Science 305, 367 -371 (2004)
Published by AAAS
From:
Takahashi (2004)
Fig. 3. Map of the 1994 distribution of Revelle factor, ({delta}PCO2/{delta}DIC)/(PCO2/DIC), averaged for
the upper 50 m of the water column
C. L. Sabine et al., Science 305, 367 -371 (2004)
Published by AAAS
Revelle Factor
The Revelle buffer factor defines how much CO2 can be absorbed by
homogeneous reaction with seawater. B = dPCO2/PCO2 / dDIC/ DIC
B = CT / PCO2 (∂PCO2/∂CT)alk = CT (∂PCO2/∂H)alk
PCO2 (∂CT/∂H)alk
After substitution
B ≈ CT / (H2CO3 + CO32-)
For typical seawater with pH = 8, Alk = 10-2.7 and CT = 10-2.7
H2CO3 = 10-4.7 and CO32- = 10-3.8; then B = 11.2
Field data from GEOSECS
Sundquist et al., Science (1979)
dPCO2/PCO2 = B dDIC/DIC
A value of 10 tells you that a change of 10%
in atm CO2 is required to produce a 1% change
in total CO2 content of seawater, By this
mechanism the oceans can absorb about half of
the increase in atmospheric CO2
B↑ as T↓ as CT↑
As B goes up it becomes harder to put CO2 into the ocean
Revelle Factor Numerical Example (using CO2Sys)
CO2 + CO32- = HCO3-
CO2
350ppm + 10% = 385ppm
Atm
Ocn
CO2 → H2CO3 → HCO3- → CO32-
at constant alkalinity
DIC
11.3 mM
1640.5 mM
183.7
1837
+1.2 (10.6%)
+27.7 (1.7%)
-11.1 (-6.0%)
+17.9 (+0.97%)
12.5
1668.2
174.2
1854.9
The total increase in DIC of +17.9 mM is mostly due to a big change
in HCO3- (+27.7 mM) countering a decrease in CO32- (-11.1 mM).
Most of the CO2 added to the ocean reacts with CO32- to make HCO3-.
The final increase in H2CO3 is a small (+1.2 mM) portion of the total.
Values of K’ versus Temperature
The values here are for S = 35, T = 25C and P = 1 atm.
Constant
K’H
K’1
K’2
K’w
Apparent Seawater Constant (K')
10-1.53
10-6.00
10-9.10
10-13.9
Specific Temperature Example (slightly different constants):
As Temp ↓ K1 and K2 get smaller (values here from Millero, 1995)
So at T = 25°C pK’1 = 5.847 K’2 = 8.916
0°C pK’1 = 6.101 K’2 = 9.376
As Temp ↓ KH gets larger
So at T = 25°C pK’H = 1.547
0°C pK’H = 1.202
How does distribution diagram change?
Is CO2 more/less soluble due to these effects?
Construct a Distribution Diagram for H2CO3 – Closed System
a. First specify the total CO2 (e.g. CT = 2.0 x 10-3 = 10-2.7 M)
b. Locate CT on the graph and draw a horizontal line for that value.
c. Locate the two system points on that line where pH = pK1 and pH = pK2.
d. Make the crossover point, which is 0.3 log units less than CT
e. Sketch the lines for the species
Annual Reviews
Annual Reviews
After Zachos et al. (2008)
Indicates “fossil fuel” added
Published by AAAS
J. C. Zachos et al., Science 308, 1611 -1615 (2005)
Walvis Ridge PETM
Weight % CaCO3
Published by AAAS
J. C. Zachos et al., Science 308, 1611 -1615 (2005)
Paleocene-Eocene Thermal
Maximum (PETM) ~ 55 Ma
Characterized by:
• Warming (5-9°C) of tropical and high latitude sea
surface temps and deep waters
• Mass extinction on sea floor (largest in last 90 m.y.)
• Increase in diversity of terrestrial fauna & flora
• Significant perturbation to the global carbon cycle
involving a large increase in greenhouse gas levels
Biogenic [clathrate] methane
(Dickens, 1995)
13C: -60‰
methane
Sources of “fossil fuel”
2300 GtC
www.explorecrete.com
Peat or Coal Oxidation
Volcanism
(Kurtz et al., 2003)
13C: -22‰
(Dickens, 1995; Schmitz et al., 2004; Svensen et
al., 2004)
13C: -7‰ or lighter (sediment
volatilization)
wildfires, no
bioturbation
> 20,000 PgC
European Space Agency www.esa.int
7000 GtC
USGS Hawaiian Volcano Observatory hvo.wr.usgs.gov/kilauea
Panchuk et al. (2007)