Total alkalinity (A_T) is one of four measurable cornerstone parameters for characterizing the marine carbonate system, yet its measurement by standard titration methods is subject to systematic misinterpretations in the presence of uncharacterized dissolved organic molecules in ocean and estuarine waters. A consequence of these misinterpretations may be the lack of thermodynamic consistency that is routinely observed among measured and calculated parameters of the carbonate system. In this work, a numerical model is used to illustrate (a) how proton-binding dissolved organic molecules influence the reported results of total alkalinity titrations in marine and estuarine settings and (b) how errors in interpretations of reported A_T values can then propagate through carbonate system calculations, thus distorting biogeochemical interpretations of calculated parameters. We examine five distinct approaches for alkalinity measurement by titration. Ideally, the difference between the measured (reported) A_T and the conventional (thermodynamic) definition of inorganic alkalinity (A_inorg) would be zero. However, in the presence of titratable organic matter, our model results show consistent non-zero differences that vary with the chemical properties of the organic matter. For all five titration approaches, the differences between reported A_T and A_inorg are greatest when the negative logarithm of the organic acid dissociation constant (pK_org) is between approximately 5 and 7. The differences between reported A_T and A_inorg also display previously undescribed variation among measurement approaches, most significantly when pK_org is between approximately 3 and 6 (typical of carboxylic acid groups). The measurement approaches that are most effective at limiting the unfavorable influence of these relatively low-pK organic acids on A_T are closed-cell titrations and single-step titrations that are terminated at a relatively high pH. For calculated carbonate system parameters relevant to in situ conditions (e.g., pH, pCO₂, calcium carbonate mineral saturation states), errors resulting from the presence of proton-binding organics are largest when calculations are based on the input pair of directly measured dissolved inorganic carbon (C_T) and directly measured A_T, and can vary in magnitude depending on the titration approach that is used to obtain A_T. The modeling results presented in this work emphasize the importance of (a) determining A_T in a manner that accounts for the ubiquity of organic alkalinity in marine and estuarine waters and (b) working toward a clearer understanding of the phenomena underlying the routine lack of internal consistency between measured versus calculated carbonate system parameters. Total alkalinity measurements should begin to incorporate either implicit or explicit evaluations of the titration characteristics of the natural organic carbon present in each sample. To that end, we recommend use of secondary titrations to directly measure organic alkalinity (sample-by-sample), characterization of relationships between total dissolved organic carbon concentrations and organic alkalinity (on local to regional scales), and/or exploration of novel curve-fitting procedures to infer the behavior of organic functional groups from titration data.

总碱度（A _T）是表征海洋碳酸盐系统的四个可测量基石参数之一，但是在海洋和河口水域中存在未表征的溶解有机分子的情况下，通过标准滴定法对其进行的测量会遭到系统的误解。这些误解的结果可能是缺乏在碳酸盐体系的测量和计算参数中常规观察到的热力学一致性。在这项工作中，使用一个数值模型来说明（a）质子结合的溶解有机分子如何影响海洋和河口环境中总碱度滴定的报告结果，以及（b）报告的A _T解释中的误差如何碳酸盐值随后可通过碳酸盐体系计算传播，从而扭曲了计算参数的生物地球化学解释。我们研究了通过滴定法测量碱度的五种不同方法。理想情况下，测得的（报告的）A _T与无机碱度（A _inorg）的常规（热力学）定义之间的差应为零。但是，在存在可滴定有机物的情况下，我们的模型结果显示出一致的非零差异，该差异随有机物的化学性质而变化。对于所有五种滴定方法，报告的A _T和A _inorg之间的差异当有机酸解离常数的负对数（p K _org）在大约5到7之间时，最大。在报告的A _T和A _inorg之间的差异也显示了以前未描述的测量方法之间的差异，当p K _org在大约3和6（通常是羧酸基）。最有效的方法是限制这些相对低p K的有机酸对A _T的不利影响闭孔滴定法和单步滴定法是在较高的pH值下终止的。对于与原位条件（例如，pH，p CO ₂，碳酸钙矿物饱和状态）相关的碳酸盐系统参数的计算，当基于直接测量的溶解物输入对进行计算时，由质子结合有机物的存在引起的误差最大。无机碳（C _T）和直接测量的A _T，其量值会取决于用于获得A _T的滴定方法。这项工作中提出的建模结果强调了（a）确定A _T的重要性以某种方式解释了海洋和河口水域中普遍存在的有机碱度；（b）致力于更清楚地了解在测量的碳酸盐系统参数与计算的碳酸盐系统参数之间通常缺乏内部一致性的现象。总碱度测量应开始对每种样品中存在的天然有机碳的滴定特性进行隐式或显式评估。为此，我们建议使用二次滴定法直接测量有机碱度（逐个样品），表征总溶解有机碳浓度与有机碱度之间的关系（在局部到区域范围内）和/或探索新曲线-拟合程序，可从滴定数据推断有机官能团的行为。