does warm or cold water take up more co 2 ?
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Does warm or cold water take up more CO2?
E Maier-Reimer, J. Segschneider, and K. Six
Max-Planck-Institute for Meteorology, Hamburg, Germany
EU FP6 IP 511176 (GOCE)
supported by CARBOOCEAN
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
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
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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:
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
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
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Inorganic carbon chemistry in sea water
transfer of CO2 from atmosphere to ocean
CO2
K0 K1 K2
CO2 + H2O HCO3- + H+ CO3
2- + 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
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Solubility and equilibrium constants
based on Weiss 1974, Millero 1995
solubility constant K0:
equilibrium constant CO2 + H2O HCO3- + H+
equilibrium constant HCO3- + H+ CO3
2- + 2 H+
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
K0 (T=30oC,S=35) =0.025mol/(kg bar)
Solubility and equilibrium constants
S=35TA=2350
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
the carbonate system at 360 ppm
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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 DICdDIC=
is no mystery!
TA=const!
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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 DICdDIC=
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
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)
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
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:
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Factor for buffering
dDIC = K0 dpCO2 (∂DIC/∂s - (∂DIC/∂h)(∂TA/∂s)/(∂TA/∂h))re
lati
ve u
nit
s
x20
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Factors for buffering: RF(pCO2, T)
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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 CO2 increases along with temperature during global warming), while the increase of the Revelle factor with rising pCO2 implies reduced uptake
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Change of pools with increasing pCO2(T)
(CO32- concentration,
not charge)
dpCO2=+1x10-5 ppm/K
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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
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
Anthropogenic CO2 in the North Atlantic
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Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al.
warm or cold? inventory divided into temperature bands
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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 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
Summary: