Salinity-based equilibrium constants are widely used to estimate trace element speciation and solve the marine carbonate system. However, this approach is necessarily limited to solutions with seawater stoichiometry. As part of SCOR Working Group 145 and a collaborative NERC/NSF-funded project, we have been developing models that use thermodynamic equilibrium constants, together with activity coefficients, taking into account the concentration-dependent effects of individual solutes on speciation. Consequently, these models are applicable to waters that depart from standard seawater composition. Total uncertainties, as well as uncertainty contributions from each individual element of the model, are calculated. Recent Ocean Sciences Meetings have provided opportunities to query the oceanographic community on model priorities and features and provide updates on progress. A draft model will be ready to share with the community at Ocean Sciences 2020!

Lunchtime event (box lunch provided) at Ocean Sciences 2020
Thursday, 20 February: 12:45 – 13:45 (SDCC, 1A, UL)
At the lunchtime event, we will review this approach and discuss necessary steps for further development and adoption by oceanographers. We will also describe and demonstrate draft software to highlight key capabilities of this approach:

1. Calculate the change in pH of a seawater Tris/TrisH⁺ buffer when the composition is altered by adding or removing different salts (web-based application)
2. Calculate how the three stoichiometric equilibrium constants for the carbonate system (K₀, K₁, and K₂) vary in response to composition changes of the seawater medium (web-based application)
3. A Python environment in which some of these types of calculations can be done interactively

SCOR Exhibit Booth at Ocean Sciences 2020

Tuesday 18 February to Thursday 20 February:  See times below 

At the SCOR booth (Booth 341) in the OSM exhibit hall, attendees will be able to have a guided hands-on experience with running the draft speciation modeling software and an opportunity to ask questions and provide feedback to the authors.
The tentative schedule for demonstration times at the SCOR booth are as follows – any updates/changes to this will be announced in the OCB and SCOR newsletters closer to OSM 2020:

• Tuesday, February 18: 11:00-12:00, 16:00-17:00
• Wednesday, February 19: 11:00-12:00, 13:00-14:00
• Thursday, February 20: 10:00-11:00, 14:00-16:00

If you are interested in learning more and/or attending these events, please fill out this expression of interest form by January 15. This will enable us to develop our booth demonstration schedule, order enough box lunches, and provide you with updates/information and access to the draft models.

Relevant science presentations at Ocean Sciences 2020

• CP34A-02 – Modelling Chemical Speciation in Seawater pH Buffers, Standard Seawater and Other Natural Waters: Applications and Uncertainties (Wed. Feb. 19, eLightning presentation)
• CP44F-1434 – Determining the Pitzer interaction coefficients of TRIS in aqueous solutions of NaCl, TRISHCl and (TRISH)₂SO₄ by solubility measurements. A new experimental contribution towards the development of a traceable chemical speciation model of pH buffers used for applications involving seawater and other natural waters (Thurs. Feb. 20, poster session 16:00-18:00)

For more information, please contact: Simon Clegg (s.clegg@uea.ac.uk) or David Turner (david.turner@marine.gu.se). Simon and David are both members of SCOR Working Group 145.