the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Metrological concepts applied to Total Alkalinity measurements in seawater: reference materials, inter-laboratory comparison and uncertainty budget
Abstract. Total alkalinity (TA) measurements in seawater are crucial for characterizing and monitoring the oceanic carbonate system. While international best practices and guidelines exist, the field still lacks widely available traceable reference materials and a well-established uncertainty budget of the measurement method. In this study, we applied key metrological principles – development of reference materials, inter-laboratory comparison and uncertainty quantification – to TA measurements. We developed two reference materials, including an artificial material with a rigorously characterized reference value and an associated uncertainty budget, being potentially traceable to the International System of units (SI). These materials were tested in an inter-laboratory comparison involving five laboratories and demonstrated the applicability and interest of the reference materials developed for quality control. Additionally, we established an uncertainty budget for the TA measurement method using two metrological approaches. The resulting expanded uncertainty was 5 µmol kg⁻¹ (k = 2) in TA, approaching the 4 µmol kg⁻¹ target set by the Global Ocean Acidification Observing Network for climate monitoring. These findings mark a significant step toward improving the quality and comparability of TA measurements, thereby strengthening long-term ocean carbonate system monitoring.
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                     RC1:  'Comment on egusphere-2025-3588', Anonymous Referee #1, 08 Oct 2025
                        
                                
                        
            
                        
            
                            
                    
            
            
            
                        The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3588/egusphere-2025-3588-RC1-supplement.pdfCitation: https://doi.org/10.5194/egusphere-2025-3588-RC1 
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                     RC2:  'Comment on egusphere-2025-3588', Anonymous Referee #2, 11 Oct 2025
                        
                                
                        
            
                        
            
                            
                    
            
            
            
                        The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3588/egusphere-2025-3588-RC2-supplement.pdf
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