Collaborative Research: Did the SE Pacific Gyre become a Hot Spot for N2 Fixation during Dusty Glacial Conditions?

合作研究：东南太平洋环流是否成为多尘冰川条件下氮气固定的热点？

• 批准号: 1602331
• 负责人: Timothy Herbert
• 金额: $ 17.77万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-15 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1602331&HistoricalAwards=false
• 关键词: Collaborative; Research; Did; SE; Pacific

The element nitrogen is a fundamental component of all living things and its cycling through the environment is an important component of Earth's biosphere. As a vital nutrient, the availability of nitrogen in a biologically usable form often "limits" the growth of plants both on land as well as in the ocean. Paradoxically, nitrogen is very abundant as dinitrogen gas (N2) in both the Earth's atmosphere and dissolved in seawater. However in this chemical form, nitrogen cannot be used by most living things. Only a small subset of microbes has the ability to "fix" N2 gas, that is, to convert it into a biologically usable chemical form. Thus, these N2 fixing organisms provide a critical environmental function sustaining life on this planet. In the ocean, N2 fixation is a major control on the total amount of biologically available nitrogen, balancing over the time losses back to N2 gas. The amount of biologically available nitrogen in turn controls the growth (productivity) of photosynthetic organisms (phytoplankton) in the sunlit region of the surface ocean which form the base of the food chain and contribute to oceanic control of the atmospheric levels of greenhouse gases. This project concerns itself with understanding the fundamental, large-scale controls of oceanic N2 fixation and how they are influenced by climate change over time. N2 fixing microbes themselves appeared to be limited by the availability of other nutrient elements such as phosphorous and iron. While it is known in which parts of the ocean there is at present greater or lesser availability of phosphorous and iron, it remains unclear if either is of overriding importance or if changes in the past produced significant variations in N2 fixation. Past changes in N2 fixation may have been an important feedback on oceanic control of atmospheric greenhouse gases. Understanding these past changes and their controls will provide the knowledge base for improving prediction of how ocean N2 fixation may respond to future changes in climate. This is of great societal relevance as changes in oceanic N2 fixation will ultimately impact marine ecosystems and living resources as feedback on the greenhouse gases driving climate change.To address these questions, the research team will undertake a study the climate-sensitivity of N2 fixation in the southeast Pacific gyre over the last glacial cycle as well as its plausible "master controls". This oligotrophic region experiences little modern N2 fixation despite proximity to a large supply of excess phosphate from the adjacent Peru-Chile oxygen minimum zone. This is consistent with modern iron limitation due to low aeolian supply that would have been relieved during past dusty conditions. The research team will use the natural experiment of the last full glacial cycle, captured in the foraminiferal-bound N isotopes of gyre sites as well as sites at its southern margin, to probe controls on the marine N cycle exerted by variable dust inputs and changes in N-loss in the adjacent oxygen minimum zone, and relate these to known changes in greenhouse forcing of climate. Through numerical modeling, the research team will also consider whether past variations in N2 fixation in this region may have impacted the global ocean N cycle and budget. This project will also fund the training of undergraduate and graduate students and support participation of high school students from underrepresented groups in original research. The research team will continue their outreach efforts through established partnerships with elementary, middle, and high schools, engaging a diverse school population and their families with exciting and relevant science.

元素氮是所有生物的基本组成部分，其在环境中的循环是地球生物圈的重要组成部分。 作为一种重要的养分，在生物学上使用的氮的可用性通常会“限制”植物在陆地和海洋上的生长。 矛盾的是，氮在地球大气中都非常丰富，因为二氮气体（N2）都溶于海水。 但是，以这种化学形式，大多数生物都不能使用氮。 只有一小部分微生物具有“固定” N2气体的能力，也就是说，将其转换为生物学上可用的化学形式。 因此，这些N2固定生物提供了在这个星球上维持生命的关键环境功能。 在海洋中，N2固定是对生物可获得的氮总量的主要控制，在时间损失中平衡到N2气体。 反过来，生物学上可用的氮量又控制着地面海洋阳光海洋地区光合生物（生产力）的生长（生产力），这形成了食物链的基础，并有助于对温室气体大气水平的海洋控制。该项目涉及了解海洋N2固定的基本，大规模控制以及它们如何随着时间的推移而受到气候变化的影响。 N2固定微生物本身似乎受到其他营养元素（例如磷和铁）的可用性的限制。 虽然目前众所周知，磷和铁的可用性越来越多，但尚不清楚要么重要的是重要性，还是过去的变化在N2固定方面产生了显着变化。 N2固定的过去变化可能是对大气温室气体海洋控制的重要反馈。 了解这些过去的变化及其控制将为改善海洋N2固定如何应对气候变化的预测提供知识库。这具有很大的社会意义，因为海洋N2固定的变化最终将影响海洋生态系统和生存资源，这是对驱动气候变化的温室气体的反馈。为了解决这些问题，研究团队将在最后一个葡萄循环中进行研究N2固定的N2固定性气候敏感性。尽管靠近相邻的秘鲁 - 智利氧气最小区域大量过量磷酸盐，但该贫营养区域几乎没有现代的N2固定。这与现代铁的限制是一致的，因为在过去的尘土飞扬的条件下，风险低的供应会得到缓解。研究小组将使用最后一个完整的冰川周期的自然实验，该实验在Gyre站点的有孔虫结合的N同位素以及其南部边缘处的位置捕获，以探测由可变的灰尘投入和n-als n-als n-als n-loss在相邻的氧气最小区域中与已知最小的变化相关的固定量变化的海洋N周期。通过数值建模，研究团队还将考虑该地区N2固定的过去差异是否可能影响全球海洋N周期和预算。该项目还将为本科和研究生的培训提供资金，并支持来自代表性不足小组的高中生参与原始研究。 研究团队将通过与小学，中学和高中建立合作伙伴关系来继续他们的外展工作，以激动人心和相关的科学吸引多样化的学校人口及其家人。