Collaborative Research: A combined boron isotope, pH microelectrode and pH-sensitive dye approach to constraining acid/base chemistry in the calcifying fluids of corals

人类活动导致大气中二氧化碳含量上升，导致海洋变得更加酸性，这可能会使珊瑚建造骨骼以及最终建造整个珊瑚礁结构更具挑战性。 珊瑚对未来海洋酸化的反应将在很大程度上取决于它们产生钙化物质的内部液体（即所谓的钙化液体）的pH值如何受到周围海水的影响。因此，必须改进目前的方法，以准确测量珊瑚钙化液的pH值，以便了解并理想地预测它们对二氧化碳引起的海洋酸化的反应。在该项目中，将采用三管齐下的方法来测量三种造礁珊瑚内钙化液的pH值，以评估其钙化液的pH值如何对实验引起的海洋酸化作出反应。这项研究将提高我们对珊瑚对海洋酸化的反应的理解，从而有可能为寻求减轻大气二氧化碳上升对海洋生态系统的有害影响的决策者和立法者提供信息。这项工作将支持三名早期职业科学家，一名博士后研究员，研究生和本科生研究助理的发展，其中一些人来自地球和海洋科学的代表性不足的群体。研究结果将通过出版物、会议报告、PI网站、教育电影、课程作业以及地区学校、博物馆和科学中心的外展活动广泛传播。珊瑚和其他类型的海洋钙化者被认为通过主动升高钙化液的pH值来开始其碳酸钙骨骼的矿化，从而将碳酸氢根离子（约占海水溶解无机碳的90%）转化为碳酸根离子，即钙化中使用的碳形式。 该项目将比较硼同位素、pH微电极和pH敏感染料方法的组合，以测量三种石珊瑚钙化液的pH值，并评估其钙化液pH值（控制其钙化的主要因素）如何对实验引起的海洋酸化作出反应。因此，这种多管齐下的方法来测量钙化液的pH值相同的珊瑚物种在同等的培养条件下，将允许这些独立的方法的有效性的第一次系统的交叉检查。该组合方法还将产生具有不确定性的钙化流体pH值，这些不确定性可以通过这些独立测量的相互比较和统计处理来量化。 重要的是，这一多管齐下的办法将用于三种珊瑚，由于其原生沃茨的碳酸盐化学性质不同，它们在钙化部位具有不同的质子调节能力;一种深冷水珊瑚（强质子泵）;一种浅温带珊瑚（中度质子泵）;一种浅热带珊瑚（弱质子泵）。本研究的目标成果包括：（1）交叉检查三种独立方法估计珊瑚钙化液pH值的有效性，（2）量化与三种方法估计珊瑚钙化液pH值相关的不确定性，（3）推进我们对珊瑚钙化的机械理解，（4）探索海洋酸化影响珊瑚钙化的机制，（5）阐明为什么珊瑚对海洋酸化表现出如此不同的反应，（6）确定最易受海洋酸化影响的珊瑚类型，（7）探索限制珊瑚在古海洋学重建中使用的所谓“生命效应”，以及（8）现有珊瑚生物矿化模型的定量约束。

The anthropogenic elevation of atmospheric CO2 is causing the oceans to become more acidic, which may make it more challenging for corals to build their skeletons and, ultimately, entire reef structures. How corals respond to future ocean acidification will largely depend on how the pH of the internal fluid from which they produce their skeletons-their so-called calcifying fluid-is impacted by the surrounding seawater. It is therefore essential that current methods are refined to accurately measure the pH of corals' calcifying fluids in order to understand and, ideally, predict their responses to CO2-induced ocean acidification. In this project, a three-pronged approach to measure calcifying fluid pH within three species of reef-forming corals will be used to assess how their calcifying fluid pH responds to experimentally induced ocean acidification. This research will improve our understanding of corals' responses to ocean acidification and thus has the potential to inform the decisions of policy makers and legislators seeking to mitigate the deleterious effects of rising atmospheric CO2 on marine ecosystems. The work will support the development of three early career scientists, a postdoctoral fellow, graduate students, and undergraduate researcher assistants-several of whom are from underrepresented groups in the earth and ocean sciences. Results will be widely disseminated through publications, conference presentations, the PIs' websites, an educational film, coursework, and outreach activities at area schools, museums, and science centers.Corals and other types of marine calcifiers are thought to begin the mineralization of their calcium carbonate skeletons by actively elevating pH of their calcifying fluid, thereby converting bicarbonate ions (comprising ~90% of seawater dissolved inorganic carbon) to carbonate ions, the form of carbon used in calcification. This project will compare the combined boron isotope, pH microelectrode, and pH-sensitive dye approach to measure the calcifying fluid pH of three species of scleractinian corals, and to assess how their calcifying fluid pH (a primary factor controlling their calcification) responds to experimentally induced ocean acidification. As a result this multi-pronged approach to measuring calcifying fluid pH of the same coral species under equivalent culturing conditions will permit the first systematic cross-examination of the validity of these independent approaches. The combined approach will also yield values of calcifying fluid pH with uncertainties that can be quantified via inter-comparison and statistical treatment of these independent measurements. Importantly, this multi-pronged approach will be used on three coral species that due to differences in the carbonate chemistry of their native waters possess differing capacities for proton regulation at their site of calcification; a deep, cold-water coral (strong proton-pumper); a shallow, temperate coral (moderate proton-pumper); and a shallow, tropical coral (weak proton-pumper). Target outcomes of this research include (1) cross-examination of the validity of three independent approaches to estimating coral calcifying fluid pH, (2) quantification of uncertainty associated with the three approaches to estimating coral calcifying fluid pH, (3) advancement of our mechanistic understanding of coral calcification, (4) exploration of the mechanism by which ocean acidification impacts coral calcification, (5) elucidation why corals exhibit such varied responses to ocean acidification, (6) identification of coral types most vulnerable to ocean acidification, (7) exploration of so-called "vital effects" that limit the use of corals in paleoceanographic reconstructions, and (8) quantitative constraint of existing models of coral biomineralization.