Collaborative Research: Constraining Planktic Foraminiferal Ecology Using Compound Specific Isotope Analysis of Amino Acids

当前的气候变化在人类历史上是独一无二的。要了解地球及其上的生命如何应对类似的变化，有必要回顾数百万年前的情况。我们对过去气候的了解有很大一部分来自海洋浮游生物的化石。具体来说，是一组被称为有孔虫的单细胞生物。有孔虫产生微小的化石壳，这些壳捕获了它们生长的水的化学成分。因此，它们可以用来重建古代的海水和气候。为了最大限度地利用有孔虫的化石壳，必须了解这种生物的生态学。有孔虫吃什么，生活在什么深度，是否有共生体等变量都会影响壳化学的解释。特定氨基酸的化合物特异性氮碳同位素（CSI-AA）是研究浮游生物中这些变量的一种独特方法。这一提议将测试这种方法在化石壳上的应用效果。如果成功，这将为描述灭绝已久的浮游有孔虫的生态学提供有力的方法。这样做，你可以更好地理解它们所持有的地球过去的记录。该项目更广泛的影响包括支持博士后研究员，发展职业机会研讨会，向主要本科院校的学生介绍地球科学研究，以及为加州大学圣克鲁斯分校有风险的STEM转校生暑期项目提供内容。具体而言，本项目将调查和开发CSI-AA的多个方面，以更好地了解浮游有孔虫的物种生态学。这是生成古气候和古海洋学记录的关键，这些记录可以说明海洋未来的气候和轨迹。拟议的项目将使用CSI-AA来限制浮游有孔虫生态学的三个关键方面：深度栖息地，饮食和共生。来自壳结合有机物的CSI-AA将首次用于有孔虫，以完善关于这些生态性状的物种水平推断。CSI-AA在现有物种中的首次应用将通过浮游生物拖曳、沉积物陷阱和圣巴巴拉盆地最近的沉积样本进行地面验证。从中吸取的经验教训将进一步应用于化石记录，以阐明已灭绝有孔虫的营养生态学。最后，氨基酸摩尔比和外消旋（随着化石时代发生的氨基酸形式之间的诊断转变）将用于评估化石中氨基酸的保存情况，并最终通过针对中新世、始新世和白垩纪的一套丰富物种来测试这种方法的局限性。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。

Current climate change is unique in human history. To understand how the Earth and life on it responds to comparable change it is necessary to look millions of years in the past. A huge amount of what we know about past climate comes from the fossils of marine plankton. Specifically, a group of single-celled organisms called foraminifera. Foraminifera make tiny fossil shells which capture the chemistry of the water they grew in. As a result, they can be used to reconstruct ancient ocean waters and climate. To use the fossil shells of foraminifera to their greatest effect, the ecology of the living creature must be understood. Variables like what the foraminifera ate, what depth it lived at, and whether it had symbionts will all impact how shell chemistry is interpreted. Compound-specific nitrogen and carbon isotopes of specific amino acids (CSI-AA) represent a unique approach to study these variables in living plankton. This proposal would test how well this approach can be applied to fossil shells. If successful, this would provide powerful ways to describe the ecology of long extinct planktic foraminifera. In doing so, one may better understand the records they hold of Earth’s past. The project broader impacts include support for a postdoctoral researcher, development of a career-opportunities workshop to introduce students from Primarily Undergraduate Institutions to geoscience research, and content contributions to a summer program for at-risk STEM transfer students at UC Santa Cruz. Specifically, this project will investigate and develop multiple aspects of CSI-AA to better understand the species-level ecology of planktic foraminifera. This is key to generating paleoclimate and paleoceanographic records that can contextualize the Ocean’s future climate and trajectory. The proposed project will use CSI-AA to constrain three key aspects of planktic foraminiferal ecology: depth habitat, diet, and symbiosis. CSI-AA from shell-bound organics will be used in foraminifera for the first time to refine species-level inferences about these ecological traits. First CSI-AA applications in extant species will be ground-truthed using plankton tows, sediment traps, and recent sedimentary samples from the Santa Barbara Basin. Lessons learned will then be applied deeper into the fossil record to elucidate the trophic ecology of extinct foraminifera. Finally, amino acid molar ratios and racemization (the diagnostic shift between amino acid forms which occurs with fossil age) will be used to assess amino acid preservation in fossils and ultimately test the limits of this approach by targeting a suite of abundant species from the Miocene, Eocene, and Cretaceous.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.