While total alkalinity (A T ) is traditionally attributed to dissolved inorganic constituents, dissolved organic matter (DOM) can significantly contribute to A T as organic alkalinity (OrgAlk), introducing errors in calculated carbonate parameters, such as the CaCO 3 saturation state (Ω) and partial pressure of CO 2 ( p CO 2 ). This study presents measurements of OrgAlk in the Arctic Ocean sea ice system and assesses its influence on carbonate speciation, with OrgAlk contributing 0.1–1.0% to A T . Sea ice brine exhibited elevated DOM and OrgAlk, with an OrgAlk/DOC ratio of 0.13 ± 0.06 µmol kg − 1 µM − 1 , consistent with global ocean values. Correcting A T for OrgAlk increased computed p CO 2 up to 84 µatm and decreased Ω ≤ 0.2 for aragonite and ≤ 0.3 for calcite compared to un-adjusted values. Elevated brine p CO 2 suggests that conventional estimates of Arctic sea ice CO 2 uptake may be overestimated when A T is used as an input parameter, particularly in spring as OrgAlk is released. The omission of OrgAlk contributed greater errors to calculated carbonate parameters than the differences in boron from using direct measurements versus salinity based ratios, highlighting the necessity of accounting for even minor OrgAlk to refine predictions of surface p CO 2 , net air-sea CO 2 flux, and the fate of CaCO 3 minerals.
Rush et al. (Tue,) studied this question.