The stoichiometric dissociation constants of carbonic acid in seawater brines from 298 to 267 K

Papadimitriou, S, Loucaides S, Rerolle VMC, Kennedy P, Achterberg EP, Dickson AG, Mowlem M, Kennedy H.  2018.  The stoichiometric dissociation constants of carbonic acid in seawater brines from 298 to 267 K. Geochimica Et Cosmochimica Acta. 220:55-70.

Date Published:



antarctic sea-ice, anthropogenic co2, Below-zero temperature, boric-acid, Brines, carbonic acid, Dissociation constants, high-frequency measurement, inorganic carbon, ocean, ph, sea ice, subzero temperatures, system, thermodynamics


The stoichiometric dissociation constants of carbonic acid (K-1C(*) and K-2C(*)) were determined by measurement of all four measurable parameters of the carbonate system (total alkalinity, total dissolved inorganic carbon, pH on the total proton scale, and CO2 fugacity) in natural seawater and seawater-derived brines, with a major ion composition equivalent to that of Reference Seawater, to practical salinity (S-P) 100 and from 25 similar to degrees C to the freezing point of these solutions and -6 degrees C temperature minimum. These values, reported in the total proton scale, provide the first such determinations at below-zero temperatures and for SP >50. The temperature (T, in Kelvin) and SP dependence of the current pK(1C)(*) and pK(2C)(*) (as negative common logarithms) within the salinity and temperature ranges of this study (33 <= S-P <= 100, -6 degrees C <= t <= 25 degrees C) is described by the following best-fit equations: pK(1C)(*) = -176.48 + 6.14528 S-P(0.5) - 0.127714 S-P + 7.396 x 10(-5) S-P(2) + (9914.37 - 622.886 S-P(0.5) P + 29.714 S-P) T-1 + (26.05129 - 0.666812 S-P(0:57)) lnT (sigma = 0.011, n = 62), and pK(2C)(*) = -323.52692 + 27.557655 S-P(0:5) + 0.154922 S-P - 2.48396 x 10(-4) S-P(2) + (14763.287 - 1014.819 S-P(0:5) - 14.35223 S-P) T-1 + (50.385807 - 4.4630415 S-P(0:5)) lnT (sigma = 0.020, n = 62). These functions are suitable for application to investigations of the carbonate system of internal sea ice brines with a conservative major ion composition relative to that of Reference Seawater and within the temperature and salinity ranges of this study. (C) 2017 Elsevier Ltd. All rights reserved.