Spectrophotometric Measurement of Carbonate Ion in Seawater over a Decade: Dealing with Inconsistencies

• Published in: Environmental Science & Technology
• Main Authors: Fernández-Guallart, E., Fajar, Noelia, García-Ibáñez, Maribel I., Castaño, Mónica, Santiago, Rocío, El Rahman Hassoun, Abed, Pérez, Fiz F., Easley, Regina, Álvarez, Marta
• Other Authors: Ministerio de Ciencia, Innovación y Universidades (España), Xunta de Galicia, National Oceanic and Atmospheric Administration (US), Natural Environment Research Council (UK), Agencia Estatal de Investigación (España), Ministerio de Ciencia e Innovación (España), European Commission, INTERREG Atlantic Area
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Chemical Society 2022
• Subjects: Ocean acidification; Saturation states; Bio-geochemistry; Oceanic carbon cycle; Time-series; CO2 system monitoring; CO2 system variables; Climate goal; Antarctic; Referencia; Cierva; Antarc*
• Online Access: http://hdl.handle.net/10261/274757; https://doi.org/10.1021/acs.est.1c06083; https://doi.org/10.13039/100000192; https://doi.org/10.13039/501100000270; https://doi.org/10.13039/501100010801; https://doi.org/10.13039/501100011033; https://doi.org/10.13039/501100000780; https://doi.org/10.13039/501100004837

With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). The spectrophotometric methodology for carbonate ion determination in seawater was first published in 2008 and has been continuously evolving in terms of reagents and formulations. Although being fast, relatively simple, affordable, and potentially easy to implement 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 data set (carbonate ion, pH, and alkalinity) obtained from 2009 to 2020 to assess the differences among the five current approaches of the methodology through an internal consistency analysis and discussing the sources of uncertainty. Overall, the results show that none of the approaches meet the climate goal (± 1 % standard uncertainty) for ocean acidification studies for the whole carbonate ion content range in this study but usually fulfill the weather goal (± 10 % standard uncertainty). The inconsistencies observed among approaches compromise the consistency of data sets among regions and through time, highlighting the need for a validated standard operating procedure for spectrophotometric carbonate ion measurements as already available for the other measurable CO2 variables. E.F.G. was supported by a Personal Técnico de Apoyo contract (PTA2016-12441-I) and N.M.F. was supported by a Juan de la Cierva postdoctoral contract (FJCI2015-24394), both from the Spanish Ministry of Science, Innovation and Universities and GAIN Grupo de Referencia Competitiva IN607A 2018/2 from Xunta de Galicia. M.I.G.-I. was supported by NOAA’s Ocean Acidification Program (OAP) via Award No. NA17OAR0170332, and by NERC’s CUSTARD (Carbon Uptake and Seasonal Traits of Antarctic Remineralisation Depths) project NE/P021263/1. A.E.R.H. was supported via the 2018 NF-POGO Shipboard Fellowship. F.F.P. was supported by the BOCATS2 (PID2019-104279GB-C21/AEI/10.13039/501100011033) ...