Gaining insights into the seawater carbonate system using discrete fCO2 measurements

García-ibáñez, Maribel I. ORCID: https://orcid.org/0000-0001-5218-0064, Takeshita, Yui, Guallart, Elisa F., Fajar, Noelia M., Pierrot, Denis, Pérez, Fiz F., Cai, Wei-Jun and Álvarez, Marta (2022) Gaining insights into the seawater carbonate system using discrete fCO2 measurements. Marine Chemistry, 245. ISSN 0304-4203

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Abstract

Understanding the ocean carbon sink and its future acidification-derived changes requires accurate and precise measurements with good spatiotemporal coverage. In addition, a deep knowledge of the thermodynamics of the seawater carbonate system is key to interconverting between measured and calculated variables. To gain insights into the remaining inconsistencies in the seawater carbonate system, we assess discrete water column measurements of carbon dioxide fugacity (fCO2), dissolved inorganic carbon (DIC), total alkalinity (TA), and pH measured with unpurified indicators, from hydrographic cruises in the Atlantic, Pacific, and Southern Oceans included in GLODAPv2.2020 (19,013 samples). An agreement of better than ±3% between fCO2 measured and calculated from DIC and pH is obtained for 94% of the compiled dataset, while when considering fCO2 measured and calculated from DIC and TA, the agreement is better than ±4% for 88% of the compiled dataset, with a poorer internal consistency for high-CO2 waters. Inspecting all likely sources of uncertainty from measured and calculated variables, we conclude that the seawater carbonate system community needs to (i) further refine the thermodynamic model of the seawater carbonate system, especially K2, including the impact of organic compounds and other acid-base systems on TA; (ii) update the standard operating procedures for the seawater carbonate system measurements following current technological and analytical advances, paying particular attention to the pH methodology that is the one that evolved the most; (iii) encourage measuring discrete water column fCO2 to further check the internal consistency of the seawater carbonate system, especially given the new era of sensor-based seawater measurements; and (iv) develop seawater Certified Reference Materials (CRMs) for fCO2 and pH together with seawater CRMs for TA and DIC over the range of values encountered in the global ocean. Our conclusions also suggest the need for a re-evaluation of the adjustments applied by GLODAPv2 to pH, which were based on DIC and TA consistency checks but not supported by fCO2 and DIC consistency.

Item Type: Article
Additional Information: Data availability: The data is publicly available in GLODAP (https://www.glodap.info/). Funding: For this work, M.I. García-Ibáñez was supported by NOAA's Ocean Acidification Program (OAP) via Award #NA17OAR0170332, and by NERC's CUSTARD (Carbon Uptake and Seasonal Traits of Antarctic Remineralisation Depths) project NE/P021263/1. N.M. Fajar was supported by grant IN607A2018/2 from the Axencia Galega de Innovación (GAIN, Xunta de Galicia, Spain). F.F. Pérez was supported by the BOCATS2 (PID2019-104279GB-C21) project funded by MCIN/AEI/10.13039/501100011033 and contributed to WATER:iOS CSIC PTI. W.-J. Cai was supported by NOAA's Ocean Acidification Program (OAP) via Award #NA17OAR0170332. M. Álvarez was supported by the RADPROF project. This work acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S).
Uncontrolled Keywords: alkalinity,atlantic ocean,carbonate chemistry,dissolved inorganic carbon,pacific ocean,pco,ph,seawater,seawater chemistry,southern ocean,spectrophotometric ph,water science and technology,chemistry(all),oceanography,environmental chemistry,sdg 14 - life below water ,/dk/atira/pure/subjectarea/asjc/2300/2312
Faculty \ School: Faculty of Science > School of Environmental Sciences
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Depositing User: LivePure Connector
Date Deposited: 26 Jul 2022 10:30
Last Modified: 13 Aug 2022 02:26
URI: https://ueaeprints.uea.ac.uk/id/eprint/86858
DOI: 10.1016/j.marchem.2022.104150

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