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Quantifying pH Dynamics in a Changing Ocean
Mathilde Hagens & Jack MiddelburgEarth Sciences
Utrecht University
Future Ocean
CO2 rich, Warmer and Low O2
• What are the consequences for ocean CO2 uptake?– Revelle factor: sensitivity of CO2 to DIC changes
• How will (seasonal and long-term) pH dynamics change?– Buffer factor: sensitivity of H+ to DIC and other
acid/base additions
pH = f (T, S, DIC, TA ….)
Total derivative of pH:
How to obtain the partial derivatives?• Numerically (small perturbations)• Analytically • Straightforward for DIC, but for TA …...
Partial derivative of TA
This buffer factor is based on the assumption that all but H+ remain constant
Sensitivity of TA to X
Buffer factor if all total concentrations are constant
Term for changes in total concentration of acid-base TotX
Term for changes in concentration of species X
where:
and
In the case of ocean acidification (X=H2CO3 and TotX=DIC):
Why this math?
• Generalised sensitivities:– Consistent with prior work by Frankignoulle (1994)
and Egleston et al. (2010)– All relevant acid-base systems
• Sensitivities:– project changes in pH dynamics– elucidate factors governing seasonal pH dynamics
• Similar approach applies to Revelle Factor
Revelle Factor extended
Revelle and Suess (1957)Sundquist et al. (1979)
• Includes all acid-base systems via partial derivative
• Consistent with prior work that included only carbon dioxide, borate and water dissociation
Sensitivity now and in 2100
Sensitivity Unit Present 2100 CO2
2100T
2100 CO2 + T
1601 2627 1517 2480
-1751 -2705 -1674 -2567
• Positive values: addition increases pH • Negative values: addition decreases pH• Ocean acidification increases sensitivity• Ocean warming lowers sensitivity
(mol kg-1)-1
(mol kg-1)-1
Projections
pH changes and gradients will increase CO2 uptake will decrease
Eutrophication and Ocean Acidification
What governs pH seasonality?
• Station ALOHA in the Pacific Ocean• Station DYFAMED in the Mediterranean Sea• Iceland Sea station in the North Atlantic
• Time series on pH, DIC, TA, T, S, borate, sulphate, fluoride, nutrients..
ALOHA
Harmonic least square fitPredicted using sensitivities
DYFAMED
Harmonic least square fitPredicted using sensitivities
Iceland Sea
Harmonic least square fitPredicted using sensitivities
Attribution of pH changes Temperature (T)Alkalinity (TA)Inorganic carbon (DIC)
Iceland SeaALOHADYFAMED
Winter pH: + T, - DICSummer pH: - T, + DIC
Winter pH: + T, - DICSummer pH: - T, + DIC
Complex pattern: T with DIC and TA
Seasonality in pH
• pH can be predicted
• TA, DIC and T most important
• T and DIC often compensate
Iceland
DyfamedBATS
Estoc
ALOHA
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
T
DIC
TA
pH a
mpl
itude
Thank you
• Generalised sensitivity factors • Extension to Revelle factor• Projections for future pH sensitivity• Understanding of pH seasonality
• Interested? PhD thesis “Impact of biogeochemical processes on pH dynamics in marine systems”
• http://dspace.library.uu.nl/handle/1874/313165.