Surface ocean pH over the last ~300 years: A synthesis and re-evaluation of coral-based reconstructions

大约三分之一的全球二氧化碳排放被海洋吸收，导致自工业化前时代以来海水酸度增加。这种现象被称为海洋酸化，不仅对许多海洋生态系统的健康构成严重威胁，而且还降低了海洋作为二氧化碳主要汇的能力，这反过来可能会加速大气中二氧化碳浓度的增加。因此，为了准确预测海洋对未来海洋酸化的化学和生物反应，必须了解自工业化前时代以来各海洋区域对大气中二氧化碳增加的反应。该项目旨在利用珊瑚骨骼重建过去300年来海洋表面酸度的历史。珊瑚骨骼的化学成分随着珊瑚生长的海水成分而变化，因此是过去海洋酸度变化的极好档案。该项目为当前和未来的海洋酸化提供了急需的历史视角。它支持一名研究生和至少一名本科生的教育和培训。本组织还通过有计划的外联活动，在当地初中和高中促进关于海洋酸化和珊瑚研究的教育，海洋酸化降低海水pH值和海水中碳酸根离子的浓度。它威胁着许多海洋生态系统的健康，特别是需要碳酸根离子来产生碳酸钙骨架的海洋钙化生物的生存。此外，它降低了海洋作为人为CO2主要汇的能力，这反过来可能会加速大气中CO2浓度的增加。然而，海水pH值的仪器记录很少，最多只跨越过去3- 40年。海洋钙化生物的碳酸盐骨骼的地球化学组成随这些生物所生活的海水的物理化学条件而变化，并提供了为数不多的机会来扩展我们对海水pH值过去变化的记录。特别是，长寿珊瑚骨骼的硼同位素组成被认为是海水pH值的一个非常有前途的替代物。然而，用海水pH值准确解释珊瑚硼同位素组成并不简单，因为越来越多的证据表明，pH值以外的许多因素，如海水温度和生物调节，也会影响珊瑚硼同位素组成。调查小组将综合和重新评估珊瑚对海洋表面pH值的限制，建立在最近对珊瑚钙化机制的更好理解的基础上。PI团队将（1）开发一种逆贝叶斯方法，用于精确重建海水pH值，考虑影响珊瑚硼同位素组成的所有因素;（2）通过将贝叶斯方法应用于已公布的珊瑚记录，在过去约300年中产生可靠的表层海洋pH值记录;（3）确定不同地点的表层海洋pH值变化的驱动因素。除了对当前和未来的海洋酸化提供急需的历史视角外，这个项目将产生一套数值方法，供社区随时使用，用于健壮的珊瑚-该奖项反映了NSF的法定使命，并通过使用基金会的智力价值进行评估，被认为值得支持和更广泛的影响审查标准。

Roughly a third of global carbon dioxide emission is absorbed by the ocean, causing an increase in seawater acidity since the pre-industrial era. This phenomenon, known as ocean acidification, not only poses serious threat to the health of many marine ecosystems, but also decreases the ocean’s capacity as a major sink for carbon dioxide which in turn will likely accelerate the increase of carbon dioxide concentration in the atmosphere. Therefore, to accurately predict ocean’s chemical and biological responses to future ocean acidification, it is essential to understand how various ocean regions have already responded to the atmospheric dioxide increase since the pre-industrial era. This project seeks to use coral skeletons to reconstruct histories of surface ocean acidity over the past ~300 years. The chemistry of coral skeletons changes with the composition of the seawater in which corals grow and is thus an excellent archive of past changes in ocean acidity. This project provides a much-needed historical perspective on the current and future ocean acidification. It supports the education and training of one graduate student and at least one undergraduate. It also promotes the education about ocean acidification and coral research in local middle and high schools through planned outreach activities.Ocean acidification reduces seawater pH and the concentration of carbonate ions in seawater. It threatens the health of many marine ecosystems, especially the survival of marine calcifying organisms that need carbonate ions to produce their calcium carbonate skeletons. Furthermore, it decreases the ocean’s capacity as a major sink for anthropogenic CO2 which in turn will likely accelerate the increase of CO2 concentration in the atmosphere. However, instrumental records of seawater pH are sparse and at most only span the last ~3-4 decades. Geochemical compositions of the carbonate skeletons of marine calcifying organism vary as a function of the physicochemical conditions of the seawater in which these organisms live, and provide one of the few opportunities to extend our records of past changes in seawater pH. In particular, the boron isotope composition of long-lived coral skeleton is regarded as a very promising proxy of seawater pH. However, accurate interpretation of coral boron isotope composition in terms of seawater pH is not straightforward, as growing evidence suggests that many factors other than pH, such as seawater temperature and biological regulation, can also influence coral boron isotope composition. The investigator team will synthesize and re-evaluate coral-based constraints on surface ocean pH, building on recent improved understanding of the mechanisms of coral calcification. The PI team will (1) develop an inverse Bayesian method for accurate seawater pH reconstruction considering all factors influencing coral boron isotope composition; (2) produce robust surface ocean pH records over the last ~300 years by applying the Bayesian method to published coral records; (3) determine the drivers of surface ocean pH variations at different sites on annual to multi-decadal scales. In addition to providing a much-needed historical perspective on the current and future ocean acidification, this project will produce a suite of numerical methods that are readily to be used by the community for robust coral-based seawater pH reconstruction and for accelerating future experimental studies in this field.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.