NOAA webinar: “Why are there so many ‘pH scales’ for measuring seawater ‘pH’ – What do these scales mean for measuring or using seawater ‘pH’?”, 26 January 2016

Date & time: 26 January 2016, 2pm – 3pm


Speaker: Andrew Dickson (SIO)

Abstract: pH is an important property of aqueous solutions because it affects a wide variety of chemical and biochemical properties through its role in acid-base reactions. This importance and the ease of pH measurement are the reasons why pH is perhaps the most measured chemical parameter in many environmental systems. A primary rationale for pH measurements is to enable calculation of the speciation in acid-base systems such as the CO2 system in seawater. However, the notional definition of pH, pH = –lg a(H+) , does not lend itself to straightforward application to seawater systems, and, as a results a number of alternate seawater ‘pH’ scales have been developed over the years. These various ‘pH’ scales have different meanings, and incorporate differing assumptions and calibration approaches, yet each of the various measurements is often simply referred to as ‘pH’, inviting confusion. This webinar will explain how these various ‘pH’ scales arose; detail how they differ; and outline the perceived advantages and disadvantages of the various approaches. Finally, it will discuss how to choose an approach that is suited to your scientific goals, and how best to implement it and use it.

About the speaker: Andrew Dickson is a professor of marine chemistry in the Marine Physical Laboratory division at the Scripps Institution of Oceanography, University of California, San Diego (UCSD). Dickson’s research focuses on improving our understanding of the chemistry of carbon dioxide in seawater, with a current emphasis on the effects of ocean acidification. He has played a key role in developing quality control standards for oceanic carbon dioxide measurements and leads a program to prepare, certify, and distribute CO2 reference materials to the world’s marine scientists. Born in Nairobi, Kenya, Dickson received a B.Sc. degree and a Ph.D from the University of Liverpool. Prior to joining Scripps, Dickson served as a postdoctoral research associate at the Marine Biological Association Laboratory in Plymouth, England and as a postdoctoral associate in the University of Florida, Department of Chemistry. He joined Scripps as an assistant research chemistry, became an associate research chemist, a professor-in-residence of marine chemistry then a professor.

Sponsor: This webinar is hosted by the US Interagency Working Group on Ocean Acidification, a collaborative working group of 13 federal agencies that aims to coordinate and foster Federal research and monitoring on ocean acidification (

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