Latest News (February 2019)

New member of our team

We are delighted to welcome postdoctoral scholar Dr Ellen Briggs to our group. She is employed at the Scripps Institution of Oceanography (SIO), and will work with Andrew Dickson on the Harned cell experiments, and heat capacity determinations, that are a part of the joint project with Simon Clegg and Matthew Humphreys at the University of East Anglia.

Ellen completed her Ph.D at SIO with Todd Martz in 2017, and the theme of her dissertation was the expansion of marine biogeochemical observations through the creation of novel autonomous sensors for constraining the aqueous carbon dioxide system. She focused on the development of solid state sensors capable of rapid (<60 s) and simultaneous measurement of pH and AT (total alkalinity) of seawater for monitoring the aqueous carbon dioxide system. Initial results with these ISFET devices indicate precision of 2-10 μmol kg-1 for AT and 0.005 for pH. They require no external reagents, have low power consumption, and meet the rugged demands required for integration with autonomous platforms. The prototype sensor has undergone preliminary field testing, and been deployed at Kaneohe Bay, Hawaii. Ellen also served as Co-Chief Scientist, in 2018, on the US GO-SHIP repeat hydrography cruise S04P. With her considerable laboratory and instrumental skills she will be a valuable contributor to our project, and to the work of SCOR WG145.

Experiments

Pablo Lodeiro and Eric Achterberg (GEOMAR, Kiel) have almost completed a large series of solubility measurements of the uncharged buffer substance Tris (or THAM, tris(hydroxymethyl)aminomethane) in aqueous NaCl solutions from 5 oC to 45 oC, and of NaCl in aqueous Tris. These measurements will help us to quantify the interactions in artificial seawater solutions containing TrisH+/Tris pH buffer that control the activity coefficients of the Tris and the pH. We will fit the results to obtain the relevant interaction parameters in the Pitzer model. This work will contribute to the accurate model of the buffer system that we are developing in order to calculate pH, and chemical speciation, for applications involving both seawater and other natural waters (of varying composition).

We are also currently analysing the results of the laboratory intercomparison exercise in which the electromotive forces of a series of test solutions were 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. One of the important findings, so far, is that the different methods of electrode construction employed at the labs, and the varying lengths of time each set of electrodes is used, can lead to significant variations in performance. In particular, the test solution containing the highest Cl- molality could not be reliably measured in some cases. We are discussing how to solve this problem, and to what extent the design of the solutions to be measured in our experimental programme needs to be altered.