Lecture 10: Ocean Carbonate Chemistry:

1
Lecture 10 Ocean Carbonate Chemistry
Ocean Distributions Ocean
Distributions Controls on Distributions
What is the distribution of CO2 added to the
ocean?
See Section 4.4 Emerson and Hedges
2
Sarmiento and Gruber (2002) Sinks for
Anthropogenic Carbon Physics Today August 2002
30-36
3
CO2 rocks HCO3- clays
CO2
River Flux
Gas Exchange
Atm
Ocn
CO2 ? H2CO3 ? HCO3- ? CO32-
Upwelling/ Mixing
H2O CH2O O2
Ca2 CaCO3
CO2
BorgC
BCaCO3
Biological Pump
Controls pH of ocean Sediment diagenesis
4
Influences on pCO2
Ko Solubility of CO2 K1, K2 Dissociation
constants Function of Temperature, Salinity
Depends on biology and gas exchange
Depends on biology only
5
Influence of Nitrogen Uptake/Remineralization on
Alkalinity
NO3- assimilation by phytoplankton 106 CO2
138 H2O 16 NO3- ? (CH2O)106(NH3)16 16
OH- 138 O2 NH3 assimilation by
phytoplankton 106 CO2 106 H2O 16 NH4 ?
(CH2O)106(NH3)16 16 H 106 O2
NO3- uptake is balanced by OH- production Alk
? NH4 uptake leads to H generation Alk ?
Alk HCO3- 2 CO32- OH- - H
See Brewer and Goldman (1976) LO Goldman and
Brewer (1980) LO
Experimental Culture
6
Air-Sea CO2 Disequilibrium
7
Emerson and Hedges Plate 8
8
Effect of El Nino on ?pCO2 fields High resolution
pCO2 measurements in the Pacific since Eq. Pac-92
Eq Pac-92 process study
PCO2sw
Always greater than atmospheric
Cosca et al. in press
El Nino Index
9
Expression of Air -Sea CO2 Flux

• Magnitude
• Mechanism
• Apply over larger space time domain

k-transfer velocity From Sc wind speed
S Solubility From SST Salinity
F k s (pCO2w- pCO2a) K ? pCO2
pCO2a
pCO2w
From CMDL CCGG network
From measurements and proxies
10
Global Map of Piston Velocity (k in m yr-1) times
CO2 solubility (mol m-3) K from satellite
observations (Nightingale and Liss, 2004 from
Boutin).
11
?pCO2 fields
Overall trends known Outgassing at low
latitudes (e.g. equatorial) Influx at high
latitudes (e.g. circumpolar) Spring blooms
draw down pCO2 (N. Atl) El Niños decrease
efflux
12
JGOFS Gas Exchange Highlight 4 -
?pCO2 fieldsTakahashi climatology
Monthly changes in pCO2w
13
Fluxes JGOFS- Global monthly fluxes
Combining pCO2 fields with k F k s (pCO2w-
pCO2a)

• On first order flux and ?pCO2 maps do not look
  that different

14
CO2 Fluxes Status
Do different parameterizations between gas
exchange and wind matter?
Global uptakes Liss and Merlivat-83 1 Pg C
yr-1 Wanninkhof-92 1.85 Pg C
yr-1 WanninkhofMcGillis-98 2.33 Pg C
yr-1 Zemmelink-03 2.45 Pg C yr-1
Yes!
Global average k (21.4 cm/hr) 2.3 Pg C yr-1
We might not know exact parameterization with
forcing but forcing is clearly important
Compare with net flux of 1.3 PgCy-1 (1.9 -
0.6) in Sarmiento and Gruber (2002), Figure 1
15
What happens to the CO2 that dissolves in water?
CO2 is taken up by ocean biology to produce a
flux of organic mater to the deep sea
(BorgC) CO2 H2O CH2O O2 Some carbon is
taken up to make a particulate flux of CaCO3
(BCaCO3) Ca2 2HCO3- CaCO3(s) CO2
H2O The biologically driven flux is called the
Biological Pump. The sediment record of BorgC
and BCaCO3 are used to unravel paleoproductivity.
The flux of BorgC to sediments drives an
extensive set of oxidation-reduction reactions
that are part of sediment diagenesis. Carbonate
chemistry controls the pH of seawater which is a
master Variable for many geochemical processes.
16
Ocean Distributions versus depth, versus ocean
Atlantic
Pacific
Points 1. Uniform surface concentrations 2.
Surface depletion - Deep enrichment 3. DIC lt
Alk 4. DDIC gt DAlk
See Key et al (2004) GBC
Q?
17
Ocean Distributions of, DIC, Alk, O2 and PO4
versus Depth and Ocean
The main features are 1. uniform surface
values 2. increase with depth 3. Deep ocean
values increase from the Atlantic to the
Pacific 4. DIC lt Alk DDIC gt DAlk 5.
Profile of pH is similar in shape to
O2. 6. Profile of PCO2 (not shown) mirrors
O2.
18
Inter-Ocean Comparison
19
Carbonate ion (CO32-) and pH decrease from
Atlantic to Pacific
x 10-3 mol kg-1 x 10-6 mol
kg-1 Alk DIC CO32- pH Surface
Water 2.300 1.950 242 8.30 North
Atlantic 2.350 2.190 109 8.03 Deep
Water Antarctic 2.390 2.280 84 7.89 Deep
Water North Pacific 2.420 2.370 57 7.71 Deep
water
Deep Atlantic to Deep Pacific DAlk
0.070 DDIC 0.180 So DAlk/DDIC 0.40
CO32- decreases from surface to deep Atlantic to
deep Pacific. These CO32- are from CO2Sys. Can
Approximate as CO32- Alk - DIC
Q? CO2Sys
20
Controls on Ocean Distributions
A) Photosynthesis/Respiration Organic matter
(approximated as CH2O for this example) is
produced and consumed as follows CH2O O2 ?
CO2 H2O Then CO2 H2O ?
H2CO3 H2CO3 ? H HCO3- HCO3- ? H
CO32- As CO2 is produced during respiration we
should observe pH ? DIC ? Alk ? PCO2 ? The
trends will be the opposite for
photosynthesis. B) CaCO3 dissolution/precipitatio
n CaCO3(s) ? Ca2 CO3 2- Also written
as CaCO3(s) CO2 H2O ? Ca2 2
HCO3- As CaCO3(s) dissolves, CO32- is added to
solution. We should observe pH ? DIC ?
Alk ? PCO2 ?
21
Photosynthesis/respiration (shown as apparent
oxygen utilization or AOU O2,sat O2,obs) and
CaCO3 dissolution/precipitation vectors (from
Park, 1969)
CH2O O2 ? CO2 H2O as O2? AOU ? CO2 ?
22
Composition of Sinking Particles and Predicted
Changes
23
Ocean Alkalinity versus Total CO2 in the
Ocean (Broecker and Peng, 1982)
24
DDIC/DAlk 1.5/1 Work Backwards DAlk / DDIC
0.66 2/3 2 mol Org C
/ 1 mol CaCO3
Emerson and Hedges Color Plate
25
What is composition of sinking particles?
Data from annual sediment traps deployments
5 g POC g m-2 y-1 / 12 g mol-1 0.4 mol C m-2 y-1
40 g CaCO3 g m-2 y-1 / 105 g mol-1 0.38 mol C
m-2 y-1
Org C / CaCO3 1
From Klaas and Archer (2002) GBC
26
PIC/POC in sediment trap samples
27
POC and CaCO3 Export Fluxes
  This Study Previous Studies
POC (Gt a-1) POC (Gt a-1) POC (Gt a-1)
Global export 9.6 3.6 11.112.9 Laws et al., 2000b
Global export 9.6 3.6 9.2 Aumont et al., 2003c
Global export 9.6 3.6 8.6 Heinze et al., 2003c
Global export 9.6 3.6 8.710.0 Gnanadesikan et al., 2004c
Global export 9.6 3.6 9.6 Schlitzer, 2004d
Global export 9.6 3.6 5.86.6 Moore et al., 2004c
CaCO3 (GtC a-1) CaCO3 (GtC a-1) CaCO3 (GtC a-1)
Global export 0.52 0.15 0.91.1 Lee, 2001b
Global export 0.52 0.15 1.8 Heinze et al., 1999c
Global export 0.52 0.15 1.64 Heinze et al., 2003c
Global export 0.52 0.15 0.680.78 Gnanadesikan et al., 2004c
Global export 0.52 0.15 0.38 Moore et al., 2004c
Global export 0.52 0.15 0.84 Jin et al., 2006c
Global export 0.52 0.15 0.54.7 Berelson et al., 2007b

Based on Global Model results of Sarmiento et al
(2992) GBC Dunne et al (2007) GBC
28
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?
29
(No Transcript)
30
Revelle Factor Numerical Example (using CO2Sys)
CO2 CO32- HCO3-
350ppm 10 385ppm
CO2
Atm
Ocn
CO2 ? H2CO3 ? HCO3- ? CO32-
DIC
11.3 mM 1.2 (10.6) 12.5
1640.5 mM 27.7 (1.7) 1668.2
183.7 -11.1 (-6.0) 174.2
1837 17.9 (0.97) 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.
31
(No Transcript)