Nitrogen isotopic (d15N) composition of carbonate-bound organic nitrogen in Deep Sea Corals: A new, high resolution proxy for N cycle studies

深海珊瑚碳酸盐结合有机氮的氮同位素 (d15N) 组成：氮循环研究的新高分辨率代理

• 批准号: 1234664
• 负责人: Maria Prokopenko
• 金额: $ 35.57万
• 依托单位: Pomona College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1234664&HistoricalAwards=false
• 关键词: Nitrogen; isotopic; d15N; composition; carbonate

The history of the nitrogen (N) cycle provides insight into the links between past climate and marine biogeochemical cycles. Interpretations of the history of the N cycle rely on the nitrogen isotopic composition (del15N) of Particulate Organic Nitrogen (del15N-PON) preserved in sedimentary "archives" such as: bulk organic nitrogen (ON) buried under suboxic/anoxic conditions in rapidly accumulating, organic-rich sediments; skeletal-bound ON in diatom frustules and foraminiferal tests, and organic skeletons of deep-sea proteinaceous corals. As is often is the case with paleo-proxies, these archives have distinct advantages and limitations, the latter including the restricted geographic occurrence of suboxic/anoxic sediments, limited temporal resolution due to bioturbation of sediments containing diatoms and foraminifera, and the limited time span for survival of the soft tissues of corals. Therefore, a multi-proxy approach is highly desirable for better understanding the patterns and causes of N cycle variability in the past. To improve upon the geographic and temporal resolution of del15N paleo-records, a scientist from Pomona College, collaborating with research groups from Claremont-McKenna College and Princeton University, will evaluate a new proxy for the history of the marine N cycle-- del15N of ON bound within the mineral lattice of deep-sea corals. Deep-sea corals can record both short-term regional and longer-term global variability in the N cycle. These organisms grow slowly, can be dated with a precision of 100 years, and have broad geographic distribution. Moreover, as demonstrated by previous research, the ON bound within the carbonate lattice is protected from diagenetic alteration. By analyzing coral specimens from disparate oceanographic environments, each chosen to represent a distinct del15N signature of PON exported from the euphotic zone, the researchers will determine whether the del15N of coral-bound ON reflects N isotopic composition of PON exported from the surface ocean. Furthermore, time-resolved records of del15N of coral-bound ON will be generated in fossil scleractinian deep-sea corals of established ages and compared to published del15N records based on more traditional proxies on decadal to millennial time scales. Much uncertainty currently exists as to which of the pools of exported PON (suspended vs. sinking) is the main food source for deep-sea corals. This issue will be addressed by comparing the del15N of modern corals from variable depths to the del15N of both suspended and sinking PON pools collected during several one-day cruises to San Pedro basin, one of the California Borderland basins.Funding for this project will support two early career female scientists and several undergraduate student research assistants from Pomona College and the new Climate Science lab in the Keck Science Department (including Claremont McKenna, Scripps, and Pitzer Colleges). Students will have an opportunity to participate in short research cruises to the San Pedro basin, to be trained in advanced analytical techniques, and present research at conferences. The results of this study will be used as topics for senior theses and independent study projects, extending the educational experience by exposing undergraduate students to both practical and intellectual aspects of climate-focused research.

氮（N）循环的历史提供了对过去气候和海洋生物地球化学循环之间联系的深入了解。氮循环历史的解释依赖于沉积物中保存的颗粒有机氮（del 15 N-PON）的氮同位素组成（del 15 N），如：大量有机氮（ON）埋藏在亚氧/缺氧条件下快速积累，富含有机物的沉积物中;硅藻壳和有孔虫测试中的硅藻结合ON，以及深海蛋白质珊瑚的有机骨架。与古代用品的情况一样，这些档案具有明显的优势和局限性，后者包括亚氧/缺氧沉积物的地理分布有限，由于含有硅藻和有孔虫的沉积物的生物扰动而导致的时间分辨率有限，以及珊瑚软组织生存的时间跨度有限。 因此，一个多代理的方法是非常可取的，更好地理解的模式和原因，在过去的N周期的变化。为了提高del 15 N古记录的地理和时间分辨率，波莫纳学院的一位科学家与克莱蒙特-麦肯纳学院和普林斯顿大学的研究小组合作，将评估海洋N循环历史的新代理--深海珊瑚矿物晶格内的ON的del 15 N。深海珊瑚可以记录氮循环中的短期区域和长期全球变化。这些生物生长缓慢，可以精确到100年，并且具有广泛的地理分布。此外，如先前的研究所示，碳酸盐晶格内的ON键被保护免受成岩蚀变。通过分析来自不同海洋环境的珊瑚标本，每个标本都被选择代表从真光层输出的PON的不同del 15 N特征，研究人员将确定珊瑚绑定ON的del 15 N是否反映从海洋表面输出的PON的N同位素组成。此外，del 15 N的珊瑚绑定ON的时间分辨记录将产生在化石石珊瑚深海珊瑚的既定年龄和发表del 15 N记录的基础上更传统的代理十年到千年的时间尺度。目前还不确定哪一个输出的PON池（悬浮还是下沉）是深海珊瑚的主要食物来源。这个问题将通过比较不同深度的现代珊瑚的del 15 N与在圣佩德罗盆地的几次为期一天的巡航中收集的悬浮和下沉PON池的del 15 N来解决，加州边境盆地之一。该项目的资金将支持两名早期职业女性科学家和来自波莫纳学院和凯克科学学院新气候科学实验室的几名本科生研究助理部门（包括克莱蒙麦肯纳，斯克里普斯和皮茨学院）。学生将有机会参加短期研究巡航到圣佩德罗盆地，接受先进的分析技术培训，并在会议上提出研究。这项研究的结果将被用作高级论文和独立研究项目的主题，通过让本科生接触以气候为重点的研究的实践和知识方面来扩展教育经验。