Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. 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 EU FP6 IP (GOCE) supported by CARBOOCEAN

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Motivation Recently, the high solubility of CO 2 in cold water has been used to argue that the polar regions are key regions for CO 2 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

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. this is meant to be a reconsideration and clarification of well known facts about carbonate chemistry rather than a piece of ongoing research! Motivation:

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Motivation to answer if warm or cold water takes up more CO 2 we need to investigate what determines ∂ 2 DIC / (∂ pCO 2 ∂ T) = ? based on and further reading: DOE Handbook of Methods for the Analysis of the Various Parameters of the Carbon Dioxide System in Sea Water Zeebe & Wolf-Gladrow, CO 2 in Seawater: Equilibrium, Kinetics, Isotopes

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. from Hooss Inorganic carbon chemistry in sea water

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Inorganic carbon chemistry in sea water transfer of CO 2 from atmosphere to ocean CO 2 K 0 K 1 K 2 CO 2 + H 2 O HCO H + CO H + K 0 = solubility (T,S,p) K 1,K 2 = equilibrium constants (T,S,p) Atmosphere Ocean solubility buffering simplified view leaving aside carbonic acid and boron compounds

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Solubility and equilibrium constants based on Weiss 1974, Millero 1995 solubility constant K 0 : equilibrium constant CO 2 + H 2 O HCO H + equilibrium constant HCO H + CO H +

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. solubility(T=30 o C,S=35) =0.025mol/(kg bar) Solubility and equilibrium constants K0K0 S=35 normalized to 1 DOE, 1994

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. K 0 (T=30 o C,S=35) =0.025mol/(kg bar) Solubility and equilibrium constants S=35 TA=2350

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. the carbonate system at 360 ppm CO 3 2- (x5) CO 2 (x100) mmol/kg B(OH) 4 - (x10) HCO3 -

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. the carbonate system at 360 ppm

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. The Revelle factor traditionally relates the changes of the carbon pools DIC and [CO2] to their actual size: (d[CO2] / [CO2]) (dDIC / DIC) some words on buffering: Revelle factor R= 1 (d[CO2] / [CO2]) R DIC dDIC= is no mystery! TA=const!

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. The Revelle factor traditionally relates the change of the carbon pools DIC and [CO2] to their actual size: (d[CO2] / [CO2]) (dDIC / DIC) Revelle factor R= TA=const! 1 (d[CO2] / [CO2]) R DIC dDIC=

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. How is the Revelle factor determined? for simplicity: s:=[CO 2 ], h:=[H + ] +[H 3 O + ]+.. (1) DIC = s(1+K 1 /h + K 1 K 2 /h 2 ) (2) TA = s(K 1 /h+2K 1 K 2 /h 2 ) + B T /(1+h/K B )+K W /h-h change of pCO 2 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)

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Revelle factor - continued- dDIC = K 0 dpCO 2 (∂DIC/∂s - (∂DIC/∂h)(∂TA/∂s)/(∂TA/∂h)) in words: The Revelle factor is the total derivative of DIC with respect to [CO 2 ] (s) or: Revelle factor is given by the ratio of the relative change of CO 2 to the relative change of DIC we only discuss the resulting terms:

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Factor for buffering dDIC = K 0 dpCO 2 (∂DIC/∂s - (∂DIC/∂h)(∂TA/∂s)/(∂TA/∂h)) relative units x20

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Factors for buffering: RF(pCO 2, T)

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Revelle factor the Revelle factor decreases with rising temperature (which may intuitively –and erroneous- imply that the uptake of anthropogenic CO 2 increases along with temperature during global warming), while the increase of the Revelle factor with rising pCO 2 implies reduced uptake

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Change of pools with increasing pCO 2 (T) (CO 3 2- concentration, not charge) dpCO 2 =+1x10 -5 ppm/K

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Surface and deep circulation (Wüst, 1950) NADW AABW Gulf Stream subtropical gyre AAIW

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Anthropogenic CO 2 in the North Atlantic

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. warm or cold? inventory divided into temperature bands

Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. 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 CO 2. This may be due to the facts that: the solubility of CO 2 in sea water is higher in cold water - however, the buffer effect is not Warm water takes up relatively more of an imposed atmospheric pCO 2 increase Ocean physics play a role: deep water formation regions are major sinks for CO 2 because of deep mixing that transports CO 2 to the ocean interior Summary: