Highlights
- Excess alkalinity (TAEX) in western Korea coastal waters reached up to 50 μmol kg−1.
- Higher TAEX was observed in lower salinity waters, emphasizing riverine contributions.
- Seasonal TAEX peaks aligned with lower DIC and AOU, suggesting biological production.
- Quantifying TAEX in coastal areas is crucial to reduce carbon parameter calculation errors.
- TAEX estimates in low-salinity water must account for calculated TA uncertainty.
Abstract
Excess alkalinity (TAEX) represents an uncharacterized component of total alkalinity (TA), which can introduce significant uncertainty in the estimation of other carbonate parameters. This effect is particularly pronounced in productive coastal regions, where the use of measured TA as an input parameter may lead to inaccurate assessment. In this study, we evaluated the seasonal variability of TAEX along the western coast of South Korea by applying an overdetermination method, which allows for the quantification of discrepancies (i.e., TAEX) between measured TA and values calculated from pH and dissolved inorganic carbon (DIC). Samples with salinity below 20 were excluded due to difficulties in accurately quantifying uncertainties in TAEX calculations, which increase significantly below this threshold. Elevated TAEX concentrations were found in waters with salinity below 25, with some instances exhibiting TAEX values reaching up to 50 μmol kg−1, suggesting riverine influence. Additionally, elevated TAEX values (> 20 μmol kg−1) were also observed in locations markedly undersaturated with respect to atmospheric CO2, indicating contributions from in-situ biological production. The high TAEX values associated with increased water transparency during autumn and winter months suggested that light penetration may significantly enhance biological activity, subsequently increasing TAEX levels. These findings highlight the importance of riverine inputs and biological processes in shaping the spatial and temporal distribution of TAEX. In the study area, TAEX should be accounted for in seawater partial pressure of CO2 (pCO2) calculations using the DIC–TA pair, as TAEX significantly influences these calculations compared to the pH–TA and pH–DIC pair.
Ko Y. H., Shin S. H., Kim S. G., Park M. O., Seok M. W., Kim M. S., Lee K. & Kim T. W., 2025. Excess alkalinity and its impacts on pCO2 estimation in coastal and estuarine waters of the Yellow Sea. Marine Chemistry: 104499. doi: 10.1016/j.marchem.2025.104499. Article (subscription required).
