Global terrestrial

1
Global terrestrial carbon estimation

• map ecosystem extents
• assume C storage (t/ha) in
• vegetation
• litter
• soils

LGM terrestrial biosphere 750-1500 Gt
smaller? (35-70 smaller?)
(Crowley, 1995)
2
Glacial atmospheric CO2 lowering must be due to
greater storage in ocean
Modern surface pCO2 (Takahashi et al., 2002)

• at equilibrium, atmospheric pCO2 determined by
  Henrys Law
• pCO2 CO2 / K0
• need mechanisms to lower CO2 or raise K0
  (solubility)

3

• dissolved inorganic carbon (DIC)
• SCO2 CO2 HCO3- CO32-
• 1 90 10
• where CO2 ? CO2(aq) H2CO3
• Therefore we can lower CO2 by
• decreasing DIC
• shifting DIC equilibrium to right
• cooling (slightly influences K1 K2)
• freshening (slightly influences K1 K2)
• alkalinityDIC change

4
Temperature salinity (effects on K values only)

• LGM temperature (colder)
• CO2 more soluble in cold waters (K0?)
• DIC also shifts away from CO2 (CO2?)
• could account for -30 ppm
• LGM salinity (saltier)
• CO2 less soluble in salty waters (K0?)
• DIC also shifts toward CO2 (CO2?)
• could result in 10 ppmv

(Takahashi et al., 2002)
5
What else determines the speciation of DIC (at
constant T, S)? Electroneutrality In any
solution, the sum of cation charges must balance
the sum of anion charges Conservative
alkalinity Excess of conservative cations over
conservative anions (conservative no change
with pH, T, or P) Alk S(conserv. cation
charges) - S(conserv. anion charges) (Na
2Mg2 2Ca2 K) - (Cl-
2SO42-) ? 2350 meq/kg
6
The conservative alkalinity excess positive
charge is balanced primarily by three
non-conservative acid-base systems DIC, boron,
and water Titration alkalinity Moles of H
equivalent to the excess of proton acceptors
(bases) over proton donors (acids) Alk ? HCO3-
2CO32- B(OH)4- OH- H
carbonate alk borate alk water alk DIC
therefore shifts to right as conservative
alkalinity increases, providing more negative
charges
7
DIC speciation and pH
H OH-

• pH and DIC systems move together in terms of
  charge
• DIC buffers pH changes
• add strong acid CO2 forms, consuming H,
  hindering pH drop

8

• Conservative alkalinity and DIC together
• increase Alk/DIC DIC shifts to right (pCO2
  drops)
• decrease Alk/DIC DIC shifts to left (pCO2
  rises)
• add Alk/DIC at 1/1 very little change in DIC
  speciation

CaCO3 Dissolution ?AlkDIC 21 Precipitation
?AlkDIC 21 Organic matter Respiration
?AlkDIC Photosynthesis ?AlkDIC CO2
gas Invasion ?AlkDIC Evasion
?AlkDIC Increase Decrease Lesser
increase Lesser decrease
9

• Carbonate system parameters
• carbonate system can be reduced to four
  interdependent, measurable parameters
• DIC
• alkalinity
• pCO2
• pH
• full characterization requires measurement of
  only two

10
Some useful approximations DIC ? HCO3-
CO32- Alk ? carbonate alk HCO3-
2CO32- Therefore HCO3- ? 2DIC Alk CO32-
? Alk DIC And since pCO2 K2HCO3-2 /
K0K1CO32- It follows that pCO2 ? K2(2DIC
Alk)2 / K0K1(Alk DIC) Using average surface
water values 1 increase in DIC gives 10
increase in pCO2 1 increase in Alk gives 10
decrease in pCO2
11

• Role of seafloor CaCO3
• Carbonate
• compensation
• CaCO3 dissolves with
• low T
• high P
• low CO32-

DIC removed
DIC added
supersaturation
under- saturation
12

• Carbonate compensation
• say, DIC added to deep ocean at start of
  glaciation
• deep ocean equilibrium shifts to left and CO32-
  drops
• seafloor CaCO3 dissolves, releasing AlkSCO2 in
  21 ratio
• pushes equilibrium back to right until CO32-
  recovers
• since initial SCO2 addition was simple
  rearrangement within ocean, whole ocean has net
  AlkSCO2 gain
• at sea surface, this shifts equilibrium to right
  (CO2 drops)