NOTICE: Due to a lapse in annual appropriations, most of this website is not being updated. Learn more.
Form submissions will still be accepted but will not receive responses at this time. Sections of this site for programs using non-appropriated funds (such as NVLAP) or those that are excepted from the shutdown (such as CHIPS and NVD) will continue to be updated.
An official website of the United States government
Here’s how you know
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Spectrophotometric Measurement of Carbonate Ion in Seawater over a Decade: Dealing with Inconsistencies
Published
Author(s)
Elisa Guallart, Noelia Fajar, Maribel García-Ibáñez, Mónica Castaño-Carrera, Rocío Santiago-Domenech, Abed El Rahman Hassoun, Fiz Pérez, Regina Easley, Marta Álvarez
Abstract
The spectrophotometric methodology for carbonate ion determination in seawater was first published in 2008 and has been continuously evolving in terms of reagents and formulation. Although the method proves to be fast, relatively simple and affordable, giving it the potential to easily be implemented in different platforms and facilities for discrete and autonomous observations, its use is not widespread in the ocean acidification community. This study uses a merged overdetermined CO2 system dataset (carbonate ion, pH and alkalinity) obtained between 2009 to 2020 to assess the differences between the five published approaches by means of an internal CO2 consistency analysis and discussion of uncertainty sources. Overall results show that neither approach meets the climate goal for ocean acidification studies (±1% standard uncertainty) but usually fulfils the weather goal (±10% standard uncertainty). The inconsistencies observed between approaches compromise the consistency of datasets between regions and in time, pointing to the need to develop a validated standard operational procedure as done for the other CO2 variables.
Guallart, E.
, Fajar, N.
, García-Ibáñez, M.
, Castaño-Carrera, M.
, Santiago-Domenech, R.
, El Rahman Hassoun, A.
, Pérez, F.
, Easley, R.
and Álvarez, M.
(2022),
Spectrophotometric Measurement of Carbonate Ion in Seawater over a Decade: Dealing with Inconsistencies, Environmental Science and Technology, [online], https://doi.org/10.1021/acs.est.1c06083, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=932191
(Accessed October 13, 2025)