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Glacial atmospheric CO 2 lowering must be due to greater storage in ocean

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

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Glacial atmospheric CO 2 lowering must be due to greater storage in ocean

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  1. 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 Henry’s Law • pCO2 = [CO2] / K0 • need mechanisms to lower [CO2] or raise K0 (solubility)

  2. 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 away from CO2 (‘to right’) • cooling (slightly influences K1 & K2) • freshening (slightly influences K1 & K2) • alkalinity:DIC change

  3. Temperature & salinity (effects on K values only) • LGM temperature (colder) • CO2more soluble in cold waters (K0) • DIC also shifts away from CO2 ([CO2]) • could account for -30 ppm • LGM salinity (saltier) • CO2less soluble in salty waters (K0) • DIC also shifts toward CO2 ([CO2]) • 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 = S(conserv. cation charges) - S(conserv. anion charges) = ([Na+] + 2[Mg2+] + 2[Ca2+] + [K+]…) - ([Cl-] + 2[SO42-]…)  2350 meq/kg

  5. The conservative alkalinity excess positive charge is balanced primarily by non-conservative anions from three systems: DIC, boron, and water Alk  [HCO3-] + 2[CO32-] + [B(OH)4-] + [OH-] – [H+] carbonate alk borate alk water alk DIC therefore shifts to right (away from CO2) as conservative alkalinity increases, providing more negative charges

  6. DIC speciation and pH H+ OH- • pH, DIC, and B systems ‘move together’ in terms of charge • DIC buffers pH changes • add strong acid: CO2 forms, consuming H+, hindering pH drop

  7. 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 CO2 gas Invasion: Alk:DIC Evasion: Alk:DIC Organic matter Respiration: Alk:DIC Photosynthesis: Alk:DIC CaCO3 Dissolution: Alk:DIC 2:1 Formation: Alk:DIC 2:1 Increase Decrease Lesser increase Lesser decrease

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

  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-] + 2[CO32-] Therefore: [HCO3-]  2DIC – Alk [CO32-]  Alk – DIC And since: pCO2 = K2[HCO3-]2 / K0K1[CO32-] 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

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