Postdoctoral Fellowship: OCE-PRF: Reconstructing CO2 Levels for the Late Cretaceous through Paleocene using Sedimentary Compositions of Molecular and Isotopic Proxies

该项目的重点是重建古代大气二氧化碳水平，为过去的“温室”条件提供关键证据，这对预测和模拟地球未来的气候至关重要。该项目研究来自保存在海洋沉积物中的古代生物的有机分子。这些分子的组成记录了环境信息，包括二氧化碳水平的证据，使其能够通过地质历史估计其大气丰度。该研究的重点是检查从南非海岸外的特兰斯凯盆地回收的沉积物芯中的分子，这些沉积物芯是在2022年国际海洋发现计划（IODP）的第392次考察期间收集的。这些沉积物是在7900万至6100万年前沉积的，当时二氧化碳水平比今天高得多，但也在上升，因此这个时间间隔为地球未来的气候提供了一个模拟。因此，该项目将促进我们对过去二氧化碳水平的理解，并寻求改进和扩展用于确定二氧化碳水平的方法。它还包括旨在扩大科学参与的举措。PI-Doiron将通过与南加州的Centralia小学区合作，吸引K-6学生，并与南非同事合作，创建与IODP Expedition 392调查结果相关的K-12宣传材料。Doiron和她的导师们还将主持一个研讨会，讨论已被证明对重建过去气候有用的分子和同位素数据范围，目的是教育对地球气候历史感兴趣的科学界成员了解这些工具。具体而言，该研究项目将通过检查植烷、姥鲛烷、烯酮和甘油二烷基甘油四醚（GDGT）。植烷是一种与植物甾醇相关的pCO 2代用品，假定主要代表叶绿素a的叶绿醇侧链，因此记录了光合作用过程中掺入生物质中的CO2。然而，由于植烷有可能来自其他来源并实现不同的生物化学功能，因此在沉积记录中直接应用该替代物时需要注意。具体而言，古细菌脂质（例如，二植烷基醚）可有助于植烷池，从而损害植烷pCO 2信号。该建议旨在通过从未成熟沉积物中的其他源特定生物标志物获得多个pCO 2记录来检查植烷代用品的准确性。它将评估和比较以下成分：（一）植烷，来自浮游植物叶绿素分解或古细菌二醚;（二）C37烯酮，是附着藻类的来源特定脂质;（三）降植烷，由叶绿素a的植基侧链或生育酚形成的分解产物;（四）GDGT，是古细菌的膜脂。它将侧重于从IODP第392次考察中恢复的特兰斯凯盆地的坎帕尼亚至古新世沉积物。总的来说，这项研究可以为提高不同生物标志物的应用做出重要贡献-基于pCO 2代用指标，并为晚白垩世至古新世期间的pCO 2浓度提供证据，这些数据稀少但与未来气候情景直接相关。该奖项反映了NSF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进行评估，被认为值得支持审查标准。

This project focuses on reconstruction of ancient atmospheric CO2 levels providing crucial evidence about past ‘greenhouse’ conditions that is critical to forecasting and modeling Earth’s future climate. This project investigates organic molecules derived from ancient organisms that are preserved in ocean sediments. The composition of these molecules records environmental information that includes evidence of CO2 levels enabling estimation of its atmospheric abundance through geological history. The study centers on examination of molecules in sediment cores recovered from the Transkei Basin off South Africa's coast that were collected during Expedition 392 of the International Ocean Discovery Program (IODP) in 2022. The sediments were deposited from 79 to 61 million years ago, when CO2 levels were much higher than today but also rising, so this time intervals provides an analog for Earth's future climate. Thus, the project will advance our understanding of past CO2 levels and seek to refine and expand the methods used for their determination. It also comprises initiatives designed to broaden scientific participation. PI-Doiron will engage K-6 students through collaboration with Centralia Elementary School District in Southern California and partner with South African colleagues to create K-12 outreach materials related to the findings from IODP Expedition 392. Doiron and her mentors will also lead a workshop to discuss the range of molecular and isotopic data that have proven useful for reconstructing past climates with the aim of educating members of the scientific community interested in Earth's climate history about these tools.Specifically, this research project will assess the comparative utility of different lipid biomarker classes as pCO2 proxies by examining the del13C values of phytane, pristane, alkenones, and glycerol dialkyl glycerol tetraethers (GDGTs). Phytane is a phytoplankton-associated pCO2 proxy assumed primarily to represent the phytol side chain of chlorophyll a, and thus records CO2 incorporated into biomass during photosynthesis. Yet, there are caveats associated with the direct application of this proxy in the sedimentary record because of the potential for phytane to derive from other sources and fulfill a different biochemical function. Specifically, archaeal lipids (e.g., diphytanyl ethers) can contribute to the phytane pool, and thereby compromise the phytane pCO2 signal. This proposal seeks to examine the veracity of the phytane proxy by obtaining multiple pCO2 records from other source-specific biomarkers in immature sediments. It will assess and compare the following components: (i) phytane, which is derived from breakdown of phytoplankton chlorophyll or from archaeal diethers; (ii) C37 alkenones, that are source-specific lipids of haptophyte algae; (iii) pristane, a breakdown product formed either from the phytyl side chain of chlorophyll a or from tocopherols; and (iv) GDGTs, which are membrane lipids in archaea. It will focus on Campanian to Paleocene sediments from the Transkei Basin recovered from IODP Expedition 392. In summary, this study can make a critical contribution toward enhancing the application of different biomarker-based pCO2 proxies and generating evidence for pCO2 concentrations during the Late Cretaceous through the Paleocene where data are sparse yet directly relevant to future climate scenarios.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.