Collaborative research: Calibration of deep-sea coral paleoproxies for nutrients, carbonate ion, and temperature

海洋与大气交换热量、水分和二氧化碳，在过去和现在的地球气候中都起着重要作用。该项目旨在通过开发地球化学工具来分析深海珊瑚化石骨骼中的微量元素，以了解和量化过去深海的物理和化学性质。这种方法有可能揭示深海关键区域的营养和碳含量以及温度在上一个冰期循环中是如何变化的，而这在以前是不可能的。该项目将与巴塞罗那的西班牙同事合作进行，他们是在水族馆养殖中维护深海珊瑚的专家。研究小组将在几个月到几年的时间里培养独居珊瑚——石竹珊瑚（Desmophyllum dianthus），同时仔细控制它们生长的海水的化学成分和温度。通过校准这些生物的碳酸钙骨架的组成，相对于实验室和现代海洋中严格控制的海水特性，研究人员将建立定量关系，使分析年代久远的珊瑚化石和推断古代珊瑚生长的海水特性成为可能。这些化石可以从海底收集并确定年代。来自新西兰周围水域的大量收藏品已经存档，这是海洋-大气相互作用的关键区域。从该地区的存档和新的海水测量中了解海水的特性，将使主要研究人员能够将实验室发现的结论与自然海洋中珊瑚生长的关系进行检验。目标是开发工具，以确定在最后一个冰期循环中，海洋生产力和气体交换对大气二氧化碳的控制程度。除了培训K-12教师外，该项目还将支持一名博士生，促进国际交流。总体而言，该项目有助于美国技术专业知识的发展，并将使人们更好地了解我们不断变化的海洋如何影响全球气候。在这个合作项目中，一名化学古海洋学家和一名海洋微地球化学专家将合作开展一项广泛的实验室实验，该实验将利用目前在自动控制的海水化学和温度下在巴塞罗那城市研究所培养的大量（150只）活石龙海。激光烧蚀ICP-MS微地球化学技术将用于精确校准骨骼P/Ca（营养物）、Ba/Ca（营养物类型）、U/Ca（碳酸盐离子）和Mg/Li（温度）指标，并研究它们对pH、进料速率、钙化速率和温度的二次敏感性。在新西兰周围广泛的水文特征良好的亚热带和亚南极水域收获的以前未开发的活收集（疏浚）石竹珊瑚也将分析这些代用物。因此，该项目将对这些新的地球化学古代用物进行补充性的实验室和实地校准，然后可以在未来的努力中使用，以精确分析珊瑚化石的年代。来自正在进行的培养实验和开放海洋档案的独特样品，结合最先进的激光烧蚀ICP-MS系统和精密微铣削技术的能力，将大大减少一组重要的D. dianthi古代用物校准的不确定性。这项工作将成为未来珊瑚古重建研究的基石。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The ocean exchanges heat, moisture, and carbon dioxide with the atmosphere and plays a large role in earth's climate, both in the past and present day. This project seeks to understand and quantify physical and chemical properties of the deep ocean in the past by developing geochemical tools to analyze trace elements in the fossil skeletons of deep-sea corals. This approach has the potential to reveal how critical regions of the deep ocean changed in nutrient and carbon content, as well as temperature, over the last glacial cycle, in ways that have not been possible previously. The project will be carried out in collaboration with Spanish colleagues in Barcelona, who are experts in the maintenance of deep-sea corals in aquarium culture. The research team will grow living cultures of the solitary coral species Desmophyllum dianthus over a period of months to years, while carefully controlling the chemical composition and temperature of the seawater in which they grow. By calibrating the composition of the calcium carbonate skeletons of these organisms relative to tightly controlled seawater properties in the laboratory and in the modern ocean, the researchers will develop quantitative relationships that enable analysis of well-dated fossil corals and inference of the properties of the seawater in which the ancient corals grew. Such fossils can be collected from the sea bottom and dated. Large collections have been archived from the waters around New Zealand, a critical region for ocean-atmosphere interactions. Knowing the seawater properties from archived and new seawater measurements in this region will allow the principal investigators to test the conclusions found in the lab against relationships seen in corals growing in the natural ocean. The goal is to develop tools to establish the degree to which atmospheric carbon dioxide was controlled over the last glacial cycle by ocean productivity and gas exchange. The project will support a PhD student and facilitate international exchange in addition to training K-12 teachers. Overall, the project contributes to technical expertise development in the US and will allow an improved understanding of how our changing ocean affects global climate.In this collaborative project, a chemical paleoceanographer and a marine microgeochemistry expert will collaborate to carry out an extensive laboratory experiment that will take advantage of a large (150 individuals) collection of living D. dianthus, currently in culture at the Institut de Ciencies del Mar-Barcelona under automatically-controlled seawater chemistry and temperature. Laser ablation ICP-MS micro-geochemical techniques will be used to calibrate precisely the skeletal P/Ca (nutrient), Ba/Ca ("nutrient-type"), U/Ca (carbonate ion) and Mg/Li (temperature) proxies, and to investigate their secondary sensitivities to pH, feeding rate, calcification rate, and temperature. A previously unexploited collection of live-collected (dredged) D. dianthus corals, harvested over a broad range of hydrographically well-characterized subtropical and subantarctic waters around New Zealand, will also be analyzed for these proxies. The project will thus result in complementary laboratory and field-based calibrations of these new geochemical paleo-proxies, that can then be used in future efforts to analyze precisely dated collections of fossil corals. The unique set of samples from ongoing culture experiments and open-ocean archives, combined with the capabilities of a state-of-the-art laser ablation ICP-MS system and precision micro-milling techniques, will reduce significantly the uncertainties in calibrations for an important set of D. dianthus-based paleoproxies. This work will serve as a cornerstone for future coral paleo-reconstruction studies.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.