News (August 2018)


We have now mostly completed a laboratory intercomparison exercise in which the electromotive forces of a series of test solutions are being measured using Harned Cells at the national metrology laboratories of Germany, France, and Japan; the National Institute of Standards and Technology; and the laboratory of WG 145 member Andrew Dickson at Scripps Institution of Oceanography (SIO) . The intercomparison involves two test solutions, one of very low ionic strength (0.1 mol kg-1) and one of high ionic strength (5.0 mol kg-1). Samples of both solutions were prepared at SIO and then distributed to all participants for measuring. Also, each laboratory prepares and measures their own samples.

Most of these laboratories are also making Harned cell measurements to contribute to the development of the speciation model. The purpose of the intercomparison is to quantify the consistency that can be expected of data from the different labs. Our first finding has been that the measurements on the very concentrated solution have highlighted differences in electrode preparation and treatment by the laboratories, which are important for our future work.


Our draft manuscript describing the needs of oceangraphers for chemical speciation modelling tools, the results of surveys of the chemical oceanography community, and reviews of modelling tools by Working Group members, is now in the final stages of preparation. It has been commented on by Working Group members, and will be submitted to Best Practices in Ocean Observing.

This month Andrew Dickson will be advertising a postdoc position at his laboratory at Scripps. The researcher will be to carry out Harned cell measurements on salt solutions, and develop novel methods for the accurate measurement of heat capacities of solutions using a differential scanning calorimeter. If you are interested, please contact

Working Group member Martha Gledhill has been awarded a grant from the German Research Council DFG to characterise the chemistry of marine dissolved organic matter using the NICA-Donnan modelling approach. The results from this project will represent an important step in extending seawater speciation models to include dissolved organic matter. The project will start in January 2019.


Simon Clegg, Andrew Dickson, and members of the national metrology laboratories of German and France will be attending the 17th ICPWS (the International Conference on the Properties of Water and Steam) in Prague at the beginning of September. There are sessions on the thermodynamic properties of seawater, and marine chemistry and seawater pH, which are very relevant to the activities of WG 145. We will be discussing our future work and its relationship to the concerns of the Joint Committe on Seawater, and particularly the development of marine pH and metrological traceability to SI units.

David Turner will be representing the Working Group at the Advanced Workshop on the Solution Chemistry of TCEs (technology-critical elements), to be held in January 2019 in Bialstock, Poland. The workshop includes consideration of  trace element speciation calculations, and the measurement of equilibrium constants and their incorporation into databases.


News (May 2018)


At GEOMAR the measurements of the solubility of Tris in aqueous NaCl solutions from 25 oC to 45 oC have now been completed, and the remaining set of experiments (for 0 oC to 20 oC) will begin shortly. As described in the news entry for April, the data will be used to help quantify the effects of Na+ and Cl ions on Tris activity coefficients and to determine the values of interaction parameters in the Pitzer speciation model we are developing.


We have just uploaded a report describing the results of our surveys of chemical oceanographers to assess their needs for chemical speciation modelling tools. This report can be found on the Publications page of this website. The survey results will inform the design of the modelling programs that are one of the outputs of the Working Group. This design is being outlined, to encourage further input from the community, in the manuscript mentioned in last month’s post.

News (April 2018)

This is a summary of news about our current activities.


Pablo at GEOMAR has just completed the first of a series of measurements of the solubility of Tris in aqueous NaCl solutions at different temperatures. The data, together with the results of Harned Cell experiments to be carried by other WG 145 members, will be used to quantify the effects of Na+ and Cl- ions on Tris activity coefficients and to determine the values of interaction parameters in the Pitzer speciation model we are developing.

At Scripps Institution of Oceanography Andrew Dickson will very shortly have a new technician “in post”, who will be carrying out many of the Harned Cell experiments that we have planned for our project. One of his first tasks, after training, will be to take part in an inter-laboratory comparison of Harned cell measurements of emfs of a small number of standard solutions. Andrew Dickson’s laboratory will produce one set of these standard solutions, batches of which will be distributed to all laboratories. In addition, each laboratory will prepare samples of the same solutions, and measure both sets. The following laboratories are taking part: Scripps Institution of oceanography, NIST (Gaithersburg, USA), PTB (Braunschweig, Germany), LNE (Paris, France), NMIJ (Japan).

We are currently discussing our project with Jelena Miladinovic and her colleagues at the Faculty of Technology and Metallurgy, University of Belgrade. They are one of relatively few groups who carry out isopiestic experiments (very accurate measurements of water activity), which would be a valuable complement to Harned Cell data (which yield HCl activity products). We hope that Jelena and her group will be able to join our collaboration and, later this year, measure water activities of some of the key mixtures of Tris and seawater salts.


David, Heather, Simon, and other members of WG 145 are preparing a manuscript describing the results of our online survey of chemical oceanographers regarding their usage/needs for chemical speciation models, and the reviews of current models carried out by WG 145 members early in the life of this Working Group. The manuscript will also contain our detailed proposals for the speciation modelling tools that will be produced by WG 145 (chemical species includes, inputs and outputs, links with “core” chemical oceanography models such as CO2SYS, etc.). It is expected that our survey results will be placed on this website, both in order to be referenced by the manuscript and for general comment.


At the beginning of September 2018, in Prague, there is an ICPWS conference (17th International Conference on the Properties of Water and Steam). Andrew Dickson will be participating in the session and workshop “Marine chemistry and seawater pH”. It is likely that Simon Clegg will attend too, in order to talk about our project. We hope other members of the collaboration will also be able to come to the meeting. The detailed programme of the conference isn’t available yet, but the website is

Working Group meeting, and Ocean Sciences 2018

Our third full Working Group meeting was held on Sunday 11 February, immediately preceding the AGU/ASLO Ocean Sciences meeting. Items for discussion included our survey of community needs for chemical speciation modelling programs, and progress in our funded project and the related experiments now being planned or carried out in several countries. The report on the Working Group meeting is now available here.

A further meeting was held on the 12th February, for the sub-group of Working Group members carrying out experiments, plus other scientists carrying out related work (Regina Easley and Jason Waters of NIST, Wei-Jun Cai of the University of Delaware, and Robert Byrne of the University of South Florida). We discussed the progress of these experiments, future plans, and links to projects outside of the Working Group. The summary of these discussions has been circulated to Working Group members.

We prepared a two page summary of WG 145 current activities and objectives which was available at the exhibit booths of both SCOR and NSF’s Ocean Carbon and Biogeochemistry programme. You are welcome to download it from the link above.

New Associate Members

We are pleased to announce that the following scientists have become Associate Members of SCOR Working Group 145: Dr Regina Easley of the National Institute of Standards and Technology of the USA, Dr Daniela Stoica of the Laboratoire national de métrologie et d’essai, Paris (France); Dr Frank Bastkowski of the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany); and Dr Igor Maksimov of the National Metrology Institute of Japan.

These associate members of the Working Group are either making new Harned Cell measurements that contribute to the development of the chemical speciation model (see an earlier 2017 post “Four institutions join the project”), or are engaged in projects that are very closely related to the aims of the Working Group. We are very grateful for their contributions, and those of their institutes.

First set of measurements completed

Our colleagues at the National Metrological Institute of Japan, Igor Maksimov and Toshiaki Asakai, have completed a set of Harned Cell measurements of HCl activities in HCl/TrisHCl solutions at different concentrations and temperatures. These data will be used to develop the chemical speciation model of Tris (2-Amino-2-hydroxymethyl-propane-1,3-diol, or THAM) buffers in seawater.They are the first of many sets of similar measurements that will be made in solutions containing Tris, TrisH+, Cl- and the inorganic components of seawater.

New postdoc to join UEA group

We are pleased to announce that Matthew Humphreys, currently working at the National Oceangraphy Centre in Southhampton, will be joining Simon Clegg at UEA. He has been appointed to a 3 year postdoc position to work on the development of the chemical speciation model. He starts work on 1 November 2017.

Matthew is a chemical oceanographer, and his field of study is the marine carbonate system. He did his Ph.D with WG 145 associate member Eric Achterberg.

Matthew’s position is supported by a grant from the Natural Environment Research Council of the UK, which is part of the UK/USA collaboration with WG 145 member Andrew Dickson (whose contribution is supported by the US National Science Foundation).

Planning the experimental programme

Simon Clegg has just completed a visit of two and a half months to the University of Gothenburg, Sweden, where he worked with WG 145 Chair David Turner. Experimental work needed for the development of the chemical speciation model was planned, and the current “state of the science” Pitzer model of artificial seawater was assembled and the parameters checked. Our initial goal is to develop a metrologically traceable model of Tris/TrisH+ buffers in artificial seawaters, as a function of both salintiy and temperature. The planned experiments reflect this, and include solutions such as Tris/TrisH+ in NaCl(aq), H+/TrisH+/Cl- solutions, and Tris/TrisH+ in aqueous NaCl/Na2SO4, for example.

The large experimental effort will be shared between Andrew Dickson at Scripps Institution of Oceanography, and our colleagues at the national metrological institutes of Germany, France, and Japan, and at GEOMAR in Kiel (Germany).

Two projects related to ours

We have recently learned of two new/recent projects that, while entirely independent of
our research, are closely related:

  • Robert (Bob) Byrne at the University of South Florida, has a three year project entitled “Development of Spectrophotometric pH Measurement Capabilities in Estuaries” (supported by NSF).
  • Wei-Jun Cai at the University of Delaware has been funded by NOAA to work on improving scientists’ ability to measure pH in dilute seawater (estuarine environments), and to evaluate the behaviour of different types of electrode. He will be collaborating with scientists at the National Institute of Standards and Technology.

We look forward to exchanging information (and collaborating, if possible) with both Bob and Wei-Jun, beginning with a web-based conference in December 2017.

Four institutions join the project

Following the success of WG 145 members Simon Clegg, Heather Benway, and Andrew Dickson in obtaining 3 year grants from NERC (in the UK) and NSF in the USA, we are very pleased to announce major additions to our collaboration:

  • Frank Bastkowski and Steffen Seitz, of Physikalisch-Technische Bundesanstalt (PTB), Braunschweig.
  • Igor Maksimov and Toshiaki Asakai, of the National Metrology Institute of Japan.
  • Daniela Stoica, of the Laboratoire national de métrologie et d’essai, Paris.
  • Pablo Lodeiro and Eric Achterberg, of GEOMAR (the Helmholtz Institute of Ocean Research, Kiel).

The first three groups will all be making Harned Cell measurements of HCl activities in solutions containing Tris/TrisH+ buffer, and the components of seawater (beginning with NaCl).

Pablo and Eric will be measuring salt solubilities in aqueous mixtures, to obtain values of the activities of the salts at saturation. They may also be carrying out potentiometric titrations.

The purpose of both types of experiments is to obtain the activities of dissolved species in the solutions, and so determine the parameters of the Pitzer the chemical speciation model we are developing. These parameters, whose values are functions of temperature and pressure, express the strength of interactions between pairs of cations and anions, and then triplets of ions (two ions of one sign, and one ion of opposite sign). They can only be determined by fitting to measurements.