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

摘要

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 ℃. 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.