Award: OCE-1744653

The work done as part of this project has been published in 3 related articlers in Marine Chemistry. These were published with their main title as "Chemical speciation models based upon the Pitzer activity coefficient equations, including the propagation of uncertainties." and with the following sub-titles: (1) Artificial seawater from 0 to 45 °C; (2) Tris buffers in artificial seawater at 25 ◦C, and an assessment of the seawater ‘Total’ pH scale; (3) Seawater from the freezing point to 45 °C, includiing acid-base equilibria. In addition, work has been done to make available code that can be used by others to replicate these calculations. This code was previewed at the 2023 OCB Workshop in Woods Hole (June 2023). As a result, the marine science communiity now has available a carefully crafted program that employs the Pitzer model for the major acid-base systems in seawater media (carbonic acid, boric acid, water) and for Tris buffer in synthetic seawater. In principle, this can be used to both to estimate the magnitude of the assumptions that have been made when using stoichiometric equilibrium constants over a range of seawater, as well as the likely uncertainty of such assumptions – a key to the ultimate traceability of marine acid-base measurements. Work is still proceeding, extending these models to include low levels of a variety of key trace metals. Also experimental work is being conducted that will improve some of the less well-defined parameters that have been identified in the papers mentioned above. Last Modified: 06/19/2023 Submitted by: Andrew G Dickson