OCE-PRF: A submicron scale investigation of foraminifera-bound organic matter: implications for preservation and the paleo-δ15N proxy

这个项目深入到浮游有孔虫的微观世界，这种微小的有壳浮游动物生活在全球各地的海洋中。当有孔虫建造贝壳时，它们会吸收少量或有机物质，并随之而来的是关于环境和生态的信息。当它们的贝壳沉入海底并聚集在一起时，它们为不断增长的地球历史档案增添了内容。在贝壳下沉和早期埋藏过程中，有机物及其原始信号到底保存得如何，是它用于重建过去气候的一个关键不确定性。为了解决这个问题，PI将使用超高分辨率晶体和化学测绘来比较贝壳在这一关键的化石记录转变之前和之后的情况。了解过去调节地球气候的反馈是我们作为一个国家应对全球变暖挑战的未来反应和准备的重要组成部分，因此与国家科学基金会的指令很好地一致。此外，通过描述现代贝壳的生物矿物结构，这项工作将有助于监测海洋酸化，这可能危及渔业、旅游业和沿海社区免受风暴(例如珊瑚礁)的自然缓冲。作为一名来自发展中国家的女科学家和移民，国际和平协会致力于鼓励其他年轻女性和代表不足的群体从事科学事业。通过与阿拉巴马州当地一所为代表不足的学生提供服务的中学合作，她希望激励那些原本可能不会将科学作为职业道路的人，在高中学习STEM科目。通过这种方式，学生们将更好地准备迎接气候变化的挑战，并意识到需要他们的天赋来建设更可持续的未来。浮游有孔虫壳壁中有机物的氮(N)同位素组成(δ15N)正在成为追踪海洋中氮的数量和分配的一种很有前途的新工具。氮是生命所必需的营养物质。近年来，与有孔虫有关的δ15N记录的数量迅速增长，为海洋肥力、氧气浓度和大气温室气体水平之间的相互作用提供了诱人的见解。然而，基本的问题仍然存在，关于方解石中N的结合机制，N吸收的分类差异，以及N结合的有机物的保存潜力，特别是在下沉和埋藏的最早阶段。大量的地球化学分析(需要结合数百个贝壳)在回答这些问题时的效用受到固有规模问题的限制。因此，国际有孔虫协会建议利用电子背向散射衍射(EBSD)和纳米尺度二次离子质谱仪(NanoSIMS)对活体(拖网捕获)和死体(海底沉积物)组合中的单个贝壳进行分析，以评估从表层海洋生物到海底埋藏的有孔虫贝壳的生物矿物结构、有机质分布和相对氮含量的变化。国际和平研究所预计，她的研究还将深入了解有机质在生物型方解石的形成(即生物矿化)和行为(例如，对破碎/溶解的敏感性、矿物-流体交换)中的作用，生物型方解石是一种广泛的科学家感兴趣的重要地质材料。因此，虽然她这项工作的具体动机是N同位素古替代物，但其影响超越了N，延伸到其他有机物质系统和相关示踪剂(例如，δ34S，I/Ca，Na/Ca)，以及基础研究领域，如宜居性和生命与行星的共同进化。关于海洋生物圈和气候之间往往复杂的反馈，古δ15N指标已经产生了高度影响的结果。因此，通过寻求为这些解释提供信息，拟议的工作有可能帮助预测海洋迅速变暖和酸化的意外后果。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project dives into the microscopic world of planktic foraminifera, tiny shelled zooplankton that inhabit oceans across the globe. As foraminifera build their shells, they incorporate tiny amounts or organic matter and, with it, information about their surroundings and ecology. When their shells sink and gather on the seafloor, they add to an ever-growing archive of Earth history. Exactly how well the organic matter and its original signals are preserved in shells during sinking and early burial is a key uncertainty for its use in reconstructing past climate. To address this, the PI will use ultra-high resolution crystal and chemical mapping to compare shells before and after this crucial transition to the fossil record. Understanding the feedbacks that have regulated Earth’s climate in the past is an essential part of our future response and preparedness as a nation to face the challenges of a warming planet, and is thus well aligned with NSF directives. Furthermore, by characterizing the biomineral structures of modern shells, this work will assist with monitoring ocean acidification, which can compromise fisheries, tourism and the natural buffering of coastal communities from storms (e.g., by coral reefs). As a female scientist and immigrant from a developing country, the PI is dedicated to encouraging other young women and underrepresented groups to pursue a career in science. By partnering with a local Alabama middle school that serves underrepresented students, she hopes to inspire those who might not otherwise consider science as a career path, to take STEM subjects in high school. In this way, students will be better equipped to take on the challenge of climate change, and be made aware of the need for their talents in building a more sustainable future.The nitrogen (N) isotope composition (δ15N) of organic matter within the shell walls of planktic foraminifera is emerging as a promising new tool for tracking the amount and partitioning of nitrogen, an essential nutrient for life, in the ocean. The number of foraminifera-bound δ15N records has grown rapidly in recent years, yielding tantalizing insights into the interplay between ocean fertility, oxygen concentrations and atmospheric greenhouse gas levels. Yet, fundamental questions remain about the mechanism of N incorporation into calcite, taxonomic differences in N uptake, and the preservation potential of the organic matter to which N is bound, particularly in the earliest stages of sinking and burial. The utility of bulk geochemical analyses (which require combining hundreds of shells) in answering these questions is limited by inherent issues of scale. Hence, the PI proposes to use electron backscatter diffraction (EBSD) and nanoscale secondary ion mass spectrometry (NanoSIMS) on individual shells from living (tow-caught) and dead (seafloor sediment) assemblages to evaluate changes in the biomineral structure, organic matter distribution and relative N content of foraminifera shells from life in the surface ocean to burial on the seafloor. The PI expects her investigation will also provide insight into the role of organic matter in the formation (i.e., biomineralization) and behavior (e.g., susceptibility to breakage/dissolution, mineral-fluid exchange) of biogenic calcite, a geologically important material of interest to a broad range of scientists. Thus while her specific motivation for this work is the N isotope paleo-proxy, the implications extend beyond N to other systems of organic matter and associated tracers (e.g., δ34S, I/Ca, Na/Ca), and to fundamental research areas like habitability and the co-evolution of life and planet. Already, the paleo-δ15N proxy is yielding high-impact results concerning the often-complex feedbacks between the marine biosphere and climate. Thus, by seeking to inform these interpretations, the proposed work has the potential to help predict the unintended consequences of a rapidly warming and acidifying ocean.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.