Over-determination of the carbonate system in natural sea-ice brine and assessment of carbonic acid dissociation constants under low temperature, high salinity, conditions

By over-determining the carbonate system in natural sea-ice brine samples, we have confirmed that stoichiometric equilibrium constants for the dissociation of carbonic acid in seawater (K-1(*),K-2(*))derived for general oceanic conditions may not be readily extrapolated to sea-ice brine systems. Dissolved inorganic carbon, total alkalinity, pH, and pCO(2) measurements in sea-ice brine have allowed us to rigorously examine the validity of K-1(*) and K-2(*) at salinities as high as 82 and in-situ temperatures as low as -4.8 degrees C. The use of seawater-derived constants yields average offsets between calculated and measured values ranging from 10% to 43% for brine salinities of 38-82. Future high-accuracy determination of sea-ice brine carbonate system components will require the specific determination of carbonate system equilibrium constants under appropriate temperature and salinity conditions. Furthermore, the community is in need of a means to evaluate the accuracy of carbonate system measurements in natural, high-salinity brine samples using the presently available analytical methods. (C) 2014 Elsevier B.V. All tights reserved.