1. Glacial atmospheric CO 2 lowering must be due to greater storage in ocean at equilibrium, atmospheric pCO 2 determined by Henry’s Law pCO 2 = [CO 2 ] / K 0 need mechanisms to lower [CO 2 ] or raise K 0 (solubility) Modern surface pCO 2 (Takahashi et al., 2002)

2. dissolved inorganic carbon (DIC):  CO 2 = [CO 2 ] + [HCO 3 - ] + [CO 3 2- ] ~1% ~90% ~10% where CO 2  CO 2 (aq) + H 2 CO 3 Therefore we can lower [CO 2 ] by: decreasing DIC shifting DIC equilibrium away from CO 2 (‘to right’) cooling (slightly influences K 1 & K 2 ) freshening (slightly influences K 1 & K 2 ) alkalinity:DIC change

3. Temperature & salinity (effects on K values only) LGM temperature (colder) CO 2 more soluble in cold waters (K 0  ) DIC also shifts away from CO 2 ([CO 2 ]  ) could account for -30 ppm LGM salinity (saltier) CO 2 less soluble in salty waters (K 0  ) DIC also shifts toward CO 2 ([CO 2 ]  ) could result in +10 ppmv (Takahashi et al., 2002)

4. Alkalinity:DIC ratio also affects 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 =  (conserv. cation charges) -  (conserv. anion charges) = ([Na + ] + 2[Mg 2+ ] + 2[Ca 2+ ] + [K+]…) - ([Cl - ] + 2[SO 4 2- ]…)  2350  eq/kg

5. The conservative alkalinity excess positive charge is balanced primarily by non-conservative anions from three systems: DIC, boron, and water Alk  [HCO 3 - ] + 2[CO 3 2- ] + [B(OH) 4 - ] + [OH - ] – [H + ] carbonate alkborate alkwater alk DIC therefore shifts to right (away from CO 2 ) as conservative alkalinity increases, providing more negative charges

6. pH, DIC, and B systems ‘move together’ in terms of charge DIC buffers pH changes add strong acid: CO 2 forms, consuming H +, hindering pH drop DIC speciation and pH H + OH -

7. Conservative alkalinity and DIC together increase Alk/DIC: DIC shifts to right (pCO 2 drops) decrease Alk/DIC: DIC shifts to left (pCO 2 rises) add Alk/DIC at 1/1: very little change in DIC speciation CO 2 gas Invasion:  Alk:DIC Evasion:  Alk:DIC Organic matter Respiration:  Alk:DIC Photosynthesis:  Alk:DIC CaCO 3 Dissolution:  Alk:DIC 2:1 Formation:  Alk:DIC 2:1 IncreaseDecrease Lesser increaseLesser decrease

8. Takahashi et al. (2002) cold photosynthesis & stratification upwelling Organic matter Respiration:  Alk:DIC Photosynthesis:  Alk:DIC

9. Carbonate system parameters carbonate system can be reduced to four interdependent, measurable parameters: DIC alkalinity pCO 2 pH full characterization requires measurement of only two

10. Some useful approximations DIC  [HCO 3 - ] + [CO 3 2- ] Alk  carbonate alk = [HCO 3 - ] + 2[CO 3 2- ] Therefore: [HCO 3 - ]  2DIC – Alk [CO 3 2- ]  Alk – DIC And since: pCO 2 = K 2 [HCO 3 - ] 2 / K 0 K 1 [CO 3 2- ] It follows that: pCO 2  K 2 (2DIC – Alk) 2 / K 0 K 1 (Alk – DIC) Using average surface water values: 1% increase in DIC gives ~10% increase in pCO 2 1% increase in Alk gives ~10% decrease in pCO 2