Collaborative Research: Refining the use of scleractinian cold-water coral skeleton-bound d15N as a proxy for marine N cycling

最近的研究表明，冷水珊瑚及其骨骼为海洋氮循环提供了有价值的信息。这些信息可以揭示驱动和响应地球气候变化的过程。冷水珊瑚遍布全球海洋，可以以年代际精度确定年代，提供过去N循环的时空记录。此外，单一骨架可以用来重建表层和深海的组成。尽管冷水珊瑚带来了希望，但我们并不完全了解它们是如何记录海洋氮循环的变化的。我们必须加强这方面的认识，然后才能利用冷水珊瑚，在不同的空间和时间、不同的珊瑚种类、不同的生活方式和摄食模式下，产生可靠的海洋氮循环记录。本项目研究了珊瑚骨架中有机氮的同位素组成与海洋氮循环特性的关系。这项研究包括一系列的实验室实验，测量从自然环境中取样的活珊瑚，以及测量来自不同海洋区域和深度地平线的珊瑚骨骼材料，这些材料都保存在博物馆中。该项目涉及圣奥拉夫学院、波莫纳学院和圣安东尼奥山学院（南加州最大的社区学院之一）的本科生。这些学生将在合作实验室与科学家和同行一起进行研究。参与该项目将培养学生的研究技能和科学知识，为深造做好准备，并为学生成为科学工作者做好准备。该项目还将开发包括YouTube视频在内的教育材料，以提高人们对海洋科学的兴趣，并提高人们对气候变化如何影响全球海洋的认识。这些教育材料将与来自代表性不足群体的高中生合作编写。研究海洋N循环历史的主要工具是从泛光带输出的颗粒有机氮（δ15N-PON）的同位素组成，可通过有孔虫试验、缺氧沉积物和软珊瑚等沉积档案获取。最近，研究表明，非共生硬核型冷水珊瑚（CWC）骨架中捕获的有机氮的δ15N记录了从海洋表面输出的δ15N- pon （Wang et al. 2014; Wang et al. 2017）。然而，为了可靠地应用CWC δ15N作为代理，我们必须解释CWC骨架内有机氮的δ15N与珊瑚生长区域输出的δ15N- pon之间约8.5‰的偏移（Wang et al. 2014）。必须考虑到δ15N偏移的性质，才能确信CWC记录的海洋N循环历史跨越空间和时间，跨越不同的珊瑚物种，以及不同生活方式条件的珊瑚。通过珊瑚培养实验、对自然环境中活珊瑚样本的测量以及不同海洋区域和不同深度的珊瑚骨骼材料档案，本研究将测试这种偏移是否源于：(1)CWC组织和骨骼之间的生物合成同位素偏移，(2)CWC组织和饮食之间不寻常的营养转移，以及/或(3)珊瑚摄食的δ15N相对于输出的δ15N- pon升高的物质。这项工作还将提供CWC中氮周转时间的估计，这将为CWC的营养生态学提供信息。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。

Refining the use of scleractinian cold-water coral skeleton-bound d15N as a proxy for marine N cyclingRecent studies show that cold-water corals and their skeletons provide valuable information about the marine nitrogen (N) cycle. This information can shed light on the processes that both drive and respond to changes in Earth’s climate. Cold-water corals are found across the global ocean and can be dated with decadal precision, offering spatial and temporal records of the N cycle in the past. In addition, a single skeleton can be used to reconstruct both surface and deep ocean composition. Despite the promise of cold-water corals, we don’t fully understand how they record changes in the marine N cycle. We must strengthen this understanding before we use cold-water corals to produce reliable records of marine N cycling across space and time, across different coral species, and under different lifestyle and feeding patterns. This project examines how the isotopic composition of organic N trapped in coral skeletons is linked to marine N cycle properties. The study includes a series of lab experiments, measurements of live corals sampled from the natural environment, and measurements of coral skeletal material from different ocean regions and depth horizons archived in museums. The project involves undergraduates at St. Olaf College, Pomona College and Mt. San Antonio College, one of the largest community colleges in Southern California. These students will conduct the research with scientists and peers in collaborating labs. Participation in the project will build student research skills and scientific knowledge for advanced study and prepare students for the scientific workforce. The project will also develop educational materials, including YouTube videos, to promote interest in marine science and awareness of how climate change influences global oceans. These educational materials will be created in collaboration with high school students from underrepresented groups. The main tool used to investigate marine N cycle history is the isotope composition of particulate organic nitrogen (δ15N-PON) exported from the euphotic zone, which can be accessed using sedimentary archives such as foraminiferal tests, anoxic sediments and soft corals. Recently, the δ15N of organic N trapped within asymbiotic scleractinian cold-water coral (CWC) skeletons has been shown to record the δ15N-PON exported from the surface ocean (Wang et al. 2014; Wang et al. 2017). In order to reliably apply CWC δ15N as a proxy, however, we must explain a ~8.5‰ offset between the δ15N of organic nitrogen within the CWC skeleton and the exported δ15N-PON in regions of coral growth (Wang et al. 2014). The nature of the δ15N offset must be accounted for to be confident that CWC records marine N cycle history consistently across space and time, across different coral species, and for corals with different lifestyle conditions. Through coral culture experiments, measurements of live corals samples from the natural environment, and archives of corals skeletal material from different ocean regions and depth horizons, this research will test whether the offset arises from: (1) a biosynthetic isotope offset between CWC tissue and skeleton, (2) an unusual trophic transfer between CWC tissue and diet, and/or (3) coral feeding on material with elevated δ15N relative to exported δ15N-PON. This work will also provide estimates of N turnover time in CWC, which are scant, and will inform trophic ecology of CWC.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.