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Does warm or cold water take up more CO 2 ?

Does warm or cold water take up more CO 2 ?. E Maier-Reimer, J. Segschneider, and K. Six. Max-Planck-Institute for Meteorology, Hamburg, Germany. supported by CARBOOCEAN. EU FP6 IP 511176 (GOCE). Motivation.

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Does warm or cold water take up more CO 2 ?

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  1. Does warm or cold water take up more CO2? E Maier-Reimer, J. Segschneider, and K. Six Max-Planck-Institute for Meteorology, Hamburg, Germany supported by CARBOOCEAN EU FP6 IP 511176 (GOCE)

  2. Motivation • Recently, the high solubility of CO2 in cold water has been used to argue that the polar regions are key regions for CO2 uptake • Is this a valid argument? • It neglects the buffer system, and, possibly, ocean dynamics • Let‘s have a more complete look at the carbonate buffer system

  3. Motivation: • this is meant to be a reconsideration and clarification of well known facts about carbonate chemistry rather than a piece of ongoing research!

  4. Motivation • to answer if warm or cold water takes up more CO2 we need to investigate what determines ∂2DIC / (∂ pCO2 ∂ T) = ? based on and further reading: DOE 1994. Handbook of Methods for the Analysis of the Various Parameters of the Carbon Dioxide System in Sea Water Zeebe & Wolf-Gladrow, 2001. CO2 in Seawater: Equilibrium, Kinetics, Isotopes

  5. Inorganic carbon chemistry in sea water transfer of CO2 from atmosphere to ocean CO2 K0 K1 K2 CO2 + H2O HCO3- + H+ CO32- + 2 H+ K0= solubility (T,S,p) K1,K2 = equilibrium constants (T,S,p) Atmosphere Ocean solubility buffering simplified view leaving aside carbonic acid and boron compounds

  6. Solubility and equilibrium constants solubility constant K0: equilibrium constant CO2 + H2O HCO3- + H+ equilibrium constant HCO3- + H+ CO32- + 2 H+ based on Weiss 1974, Millero 1995

  7. Solubility and equilibrium constants K0 (T=30oC,S=35) =0.025mol/(kg bar) S=35 TA=2350

  8. the carbonate system at 360 ppm

  9. some words on buffering: Revelle factor • The Revelle factor traditionally relates the changes of the carbon pools DIC and [CO2] to their actual size: (d[CO2] / [CO2]) (dDIC / DIC) is no mystery! R= TA=const! 1 (d[CO2] / [CO2]) R DIC dDIC=

  10. Revelle factor • The Revelle factor traditionally relates the change of the carbon pools DIC and [CO2] to their actual size: (d[CO2] / [CO2]) (dDIC / DIC) R= TA=const! 1 (d[CO2] / [CO2]) R DIC dDIC=

  11. How is the Revelle factor determined? for simplicity: s:=[CO2], h:=[H+] +[H3O+]+ .. (1) DIC = s(1+K1/h + K1K2/h2) (2) TA = s(K1/h+2K1K2/h2) + BT/(1+h/KB)+KW/h-h change of pCO2 yields change in s and h: (3) dDIC = ∂DIC/∂s ds + ∂DIC/∂h dh (4) dTA = ∂TA/∂s ds + ∂TA/∂h dh (=0) (5) dh/ds = - (∂TA/ ∂s ) / (∂TA/ ∂h ) |using dTA=0, and Henry‘s law inserting (5) into (3) and derivation with respect to s yields: (6) dDIC/ds=(∂DIC/∂s)ds - (∂DIC/∂h) ((∂TA/∂s)/(∂TA/∂h)) explicit differentiation and multiplication of (6) yields (quite) lengthy expression (Zeebe&Wolf-Gladrow, p 71/72)

  12. Revelle factor - continued- dDIC = K0 dpCO2 (∂DIC/∂s - (∂DIC/∂h)(∂TA/∂s)/(∂TA/∂h)) in words: The Revelle factor is the total derivative of DIC with respect to [CO2] (s) or: Revelle factor is given by the ratio of the relative change of CO2 to the relative change of DIC we only discuss the resulting terms:

  13. Factor for buffering dDIC = K0 dpCO2(∂DIC/∂s - (∂DIC/∂h)(∂TA/∂s)/(∂TA/∂h)) x20 relative units

  14. Factors for buffering: RF(pCO2, T)

  15. Revelle factor the Revelle factor decreases with rising temperature (which may intuitively –and erroneous- imply that the uptake of anthropogenic CO2 increases along with temperature during global warming), while the increase of the Revelle factor with rising pCO2 implies reduced uptake

  16. Change of pools with increasing pCO2(T) (CO32- concentration, not charge) dpCO2=+1x10-5 ppm/K

  17. Surface and deep circulation (Wüst, 1950) subtropical gyre Gulf Stream AAIW NADW AABW

  18. Anthropogenic CO2 in the North Atlantic

  19. warm or cold? inventory divided into temperature bands

  20. Summary: Recent discussions indicate that some confusion may be prevalent in the climate research community about the role of cold water in the uptake of anthropogenic CO2. This may be due to the facts that: • the solubility of CO2 in sea water is higher in cold water - however, the buffer effect is not • Warm water takes up relatively more of an imposed atmospheric pCO2 increase • Ocean physics play a role: deep water formation regions are major sinks for CO2 because of deep mixing that transports CO2 to the ocean interior

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