Excess alkalinity and its impacts on pCO2 estimation in coastal and estuarine waters of the Yellow Sea

초록

Excess alkalinity (TA(EX)) 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 TA(EX) along the western coast of South Korea by applying an overdetermination method, which allows for the quantification of discrepancies (i.e., TA(EX)) 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 TA(EX) calculations, which increase significantly below this threshold. Elevated TA(EX) concentrations were found in waters with salinity below 25, with some instances exhibiting TA(EX) values reaching up to 50 mu mol kg(-1), suggesting riverine influence. Additionally, elevated TA(EX) values (> 20 mu mol kg(-1)) were also observed in locations markedly undersaturated with respect to atmospheric CO2, indicating contributions from in-situ biological production. The high TA(EX) values associated with increased water transparency during autumn and winter months suggested that light penetration may significantly enhance biological activity, subsequently increasing TA(EX) levels. These findings highlight the importance of riverine inputs and biological processes in shaping the spatial and temporal distribution of TA(EX). In the study area, TA(EX) should be accounted for in seawater partial pressure of CO2 (pCO(2)) calculations using the DIC-TA pair, as TA(EX) significantly influences these calculations compared to the pH-TA and pH-DIC pair.

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