Organic alkalinity is a poorly understood component of total titration alkalinity in aquatic environments. Using a numerical method, the effects of organic acid (HOA) and its conjugate base (OA⁻) on seawater carbonate chemistry and buffer behaviors, as well as those in a hypothetical estuarine mixing zone, are explored under both closed- and open-system conditions. The simulation results show that HOA addition leads to pCO₂ increase and pH decrease in a closed system when total dissolved inorganic carbon (DIC) remains the same. If opened to the atmosphere (pCO₂ = 400 µatm), CO₂ degassing and re-equilibration would cause depressed pH compared to the unperturbed seawater, but the seawater buffer to pH change \(\left( {\beta _{{{\text{DIC}}}} \, = \left( {\frac{{\partial \ln \left( {\left[ {{\text{H}}^{ + } } \right]} \right)}}{{\partial {\text{DIC}}}}} \right)^{{ - 1}} } \right)\) indicates that weaker organic acid (i.e., higher pK_a) results in higher buffer capacity (greater β_DIC) than the unperturbed seawater. In comparison, OA⁻ (with accompanying cations) in the form of net alkalinity addition leads to pCO₂ decrease in a closed system. After re-equilibrating with the atmosphere, the resulting perturbed seawater has higher pH and β_DIC than the unperturbed seawater. If river water has organic alkalinity, pH in the estuarine mixing zone is always lower than those caused by a mixing between organic alkalinity-free river (at constant total alkalinity) and ocean waters, regardless of the pK_a values. On the other hand, organic alkalinity with higher pK_a provides slightly greater β_DIC in the mixing zone, and that with lower pK_a either results in large CO₂ oversaturation (closed system) or reduced β_DIC (in mid to high salinity in the closed system or the entire mixing zone in the open system). Finally, despite the various effects on seawater buffer through either HOA or OA⁻ addition, destruction of organic molecules including organic alkalinity via biogeochemical reactions should result in a net CO₂ loss from seawater. Nevertheless, the significance of this organic alkalinity, especially that comes from organic acids that are not accounted for under the currently recognized “zero proton level” (Dickson in Deep Sea Res 28:609–623, 1981), remains unknown thus a potentially interesting and relevant research topic in studying oceanic alkalinity cycle.

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有机碱度对海水缓冲能力的影响：数值研究

在水生环境中，有机碱度是总滴定碱度的一个鲜为人知的成分。使用数值方法，有机酸（HOA）及其共轭碱（OA的影响^- ）上海水碳酸盐化学和缓冲行为，以及那些在一个假设的河口混合区，都闭环和开系统下探索条件。模拟结果表明，当总溶解无机碳（DIC）保持不变时，封闭系统中HOA的添加会导致p CO _2的增加和pH值的降低。如果向大气开放（p CO ₂  = 400 µatm），则CO ₂与未扰动的海水相比，脱气和重新平衡将导致pH值降低，但是海水缓冲剂会改变pH值\（\ left（{\ beta _ {{{\ text {DIC}}}}} \，= \ left（{\压裂{{\ partial \ ln \ left（{\ left [{{\ text {H}} ^ {+}} \ right]} \ right）}} {{\ partial {\ text {DIC}}}}}} \右）^ {{ - 1}}} \右）\）表示弱有机酸（即，更高的pK_一）在更高的缓冲能力（更大的成果β _DIC）比未受扰动的海水。相比较而言，OA ^{- （}伴随阳离子）在净碱度此外引线的形式，以p CO ₂在封闭系统中减少。与大气重新平衡后，将所得扰动海水具有较高的pH和β _DIC比未受扰动的海水。如果河水具有有机碱度，则河口混合区中的pH总是低于无有机碱河（总碱度恒定）与海水混合引起的pH，而与pK _a值无关。在另一方面，具有较高的有机碱度的pK_一个提供稍大β _DIC在混合区中，并且具有较低的pK_一个在大CO任一结果₂的过饱和（密闭系统）或降低β _DIC（在封闭系统中或在开放系统中的整个混合区中达到高盐度）。最后，尽管通过任HOA或OA上海水缓冲器的各种效果^-此外，破坏的有机分子，包括生物地球化学经由反应有机碱度应导致二氧化碳净₂从海水损失。然而，这种有机碱的重要性，特别是来自目前公认的“零质子水平”下没有考虑的有机酸（Dickson in Deep Sea Res 28：609-623，1981），仍然未知，因此潜在地有趣和研究海洋碱度循环的相关研究课题。