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

大气二氧化碳的人为升高正在导致海洋变得更加酸性，这可能会使珊瑚建造骨骼并最终建造整个珊瑚礁结构变得更具挑战性。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骨骼的内部液体--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，准确测量珊瑚钙化流体的pH值，以便了解并最好是预测它们对二氧化碳引起的海洋酸化的反应。在这个项目中，将使用一种三管齐下的方法来测量三种珊瑚礁形成珊瑚中的钙化流体pH值，以评估它们的钙化流体pH值对实验诱导的海洋酸化的反应。这项研究将提高我们对珊瑚对海洋酸化反应的理解，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政策制定者和立法者的决策提供信息。这项工作将支持三名早期职业科学家的发展，他们是一名博士后、研究生和本科生研究员助理-其中几人来自地球和海洋科学中代表性较低的群体。研究结果将通过出版物、会议报告、PIs网站、教育影片、课程和地区学校、博物馆和科学中心的推广活动广泛传播。珊瑚和其他类型的海洋钙化剂被认为通过主动提高其钙化流体的pH值，开始其碳酸钙骨架的矿化，从而将碳酸氢根离子(占海水溶解的无机碳的90%)转化为碳酸盐离子，碳酸盐离子用于钙化作用。该项目将比较硼同位素、pH微电极和pH敏感染料的组合方法来测量三种硬珊瑚的钙化液pH，并评估它们的钙化液pH(控制它们钙化的主要因素)对实验诱导的海洋酸化的反应。因此，这种多管齐下的方法在同等养殖条件下测量同一珊瑚物种的钙化液pH值，将使首次系统地交叉检查这些独立方法的有效性。这种结合的方法还将产生钙化液pH值的值，这些值的不确定度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，这种多管齐下的办法将用于三种珊瑚：一种是深水冷水珊瑚(强质子泵珊瑚)；一种浅水温带珊瑚(中等质子泵珊瑚)；以及一种浅水热带珊瑚(弱质子泵珊瑚)。这项研究的目标成果包括：(1)对估算珊瑚钙化流体pH的三种独立方法的有效性进行交叉检验，(2)量化与估算珊瑚钙化流体pH的三种方法相关的不确定性，(3)促进我们对珊瑚钙化的机理的理解，(4)探索海洋酸化影响珊瑚钙化的机制，(5)阐明珊瑚对海洋酸化表现出如此不同的反应，(6)确定最容易受到海洋酸化影响的珊瑚类型，(7)探索在古海洋重建中限制使用珊瑚的所谓“生命效应”，(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.