Ocean Acidification: Collaborative Research: Investigation of seawater CO2 system thermodynamics under high pCO2 conditions

评估高二氧化碳世界中海洋酸化的影响需要约束良好的模型，这些模型将可测量的碳系统参数相互关联：总溶解无机碳（CT）和总碱度（AT）、二氧化碳逸度（fCO2）、pH值和碳酸盐离子浓度（[co32 -]）。使用碳酸解离常数（K1‘和K2’）将CT和AT与fCO2联系起来用于海水分析的当前热力学模型已被证明在当前fCO2值约为380单位大气压时提供了良好的结果，但在本世纪末之前可能出现的二氧化碳浓度升高（500单位大气压）时就失效了。二氧化碳升高对生物和生态系统功能的影响的研究需要强大的热力学模型，以确保偶尔只涉及两个系统变量的测量结果能够提供对所研究系统整体的准确描述。由于对海洋酸化后果的准确预测对于指导管理和政策决策至关重要，因此开发准确的CO2热力系统模型至关重要。在这个项目中，南佛罗里达大学和SRI国际的研究人员将对CT、at、fCO2和pH进行最佳实践测量，随后评估K1‘、K2’和KB'的大小，从而产生海洋二氧化碳系统内部一致的热力学模型。拟议的工作得益于(a)最近开发和表征用于精确和准确海水pH测量的纯化指标，以及(b)开发准确的硼酸盐与盐度比率，从而更好地说明硼酸对海水缓冲强度的贡献。该研究将包括调查未表征的海水原质（例如来自溶解有机物）的AT贡献，以及碳酸盐和硼酸盐离子之间可能的相互作用，这些相互作用可能影响高pCO2条件下的CO2平衡。最近发展的用于直接测量海水中碳酸盐离子浓度的紫外光谱法将进一步促进拟议的工作。更广泛的影响：OCB海洋酸化首席研究员研讨会报告（2011年）确定了近期需要“确定碳酸盐系统的大pH变化的后果；随着pH值的变化，碳酸盐系统的反应可能与我们通常测量的范围不同。”由于对CO2系统扰动实验结果的解释依赖于对实验所依据的碳系统参数的准确了解，因此发展改进的碳系统平衡关系，特别是在高CO2水平下，对海洋酸化的研究至关重要。参与该项目的研究生和本科生将受益于学习碳系统的最佳实践以及对二氧化碳系统热力学的全面了解。现场组件将提供海上测量和CO2系统关系统计分析的实践经验。此外，我们打算开发一个海洋酸化教室和实验室模块，将在当地一所高中教授，服务于种族多样化的学生群体。在这次活动中制定的课程计划将在一年一度的皮内拉斯县高中科学/数学全区培训会上提交给教师。

Assessments of the effects of ocean acidification in a high CO2 world require well-constrained models that interrelate measurable carbon system parameters: total dissolved inorganic carbon (CT) and total alkalinity (AT), CO2 fugacity (fCO2), pH and carbonate ion concentration ([CO3 2-]). Current thermodynamic models that relate CT and AT to fCO2 using carbonic acid dissociation constants (K1' and K2') developed for seawater analyses have been shown to provide good results at current fCO2 values ca. 380 uatm, but break down at the elevated CO2 concentrations (500 uatm) that are likely to occur before the end of this century. Studies of the effects of elevated CO2 on organismal and ecosystem functions require robust thermodynamic models to ensure that results, which occasionally involve measurements of only two system-variables, provide accurate depictions of the investigated system in its entirety. Because accurate predictions of the consequences of ocean acidification are critical to guide management and policy decisions, development of accurate thermodynamic CO2 system models is essential.In this project, researchers at the University of South Florida and SRI International will perform best practices measurements of CT, AT, fCO2 and pH, and subsequently assess the magnitudes of K1', K2' and KB' that produce an internally consistent thermodynamic model of the marine CO2 system. The proposed work is facilitated by (a) the recent development and characterization of purified indicators for precise and accurate seawater pH measurements and (b) the development of accurate borate to salinity ratios that provide an improved account of the contributions of boric acid to the buffer intensity of seawater. The study will include investigations of the AT contributions of uncharacterized seawater protolytes (e.g. from dissolved organic matter) as well as the possible interactions between carbonate and borate ions that may influence CO2 equilibria under high pCO2 conditions. The proposed work will additionally be promoted by the recent development of UV spectrometric procedures for direct measurements of carbonate ion concentrations in seawater.Broader Impacts: The OCB Ocean Acidification Principal Investigator Workshop Report (2011) identified a near-term need to "determine the consequences of large pH change on the carbonate system; as pH shifts the carbonate system may respond in ways different from the range we customarily measure". Since interpretation of the results of CO2 system perturbation experiments depend on accurate knowledge of the carbon system parameters under which the experiments were performed, development of improved carbon system equilibrium relationships, especially at high CO2 levels, is vitally important to the study of ocean acidification.Graduate and undergraduate students involved in the project will benefit from learning carbon system best practices as well as obtaining a comprehensive understanding of CO2 system thermodynamics. The field component will provide hands-on experience in at sea measurements and statistical analysis of CO2 system relationships. Furthermore, we intend to develop an ocean acidification classroom and laboratory module that will be taught at a local high school serving an ethnically-diverse student population. The lesson plans developed during this activity will be presented to teachers at the annual District-wide Training for High School Science/Math for Pinellas County schools.