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

博士后奖学金：OCE-PRF：利用分子和同位素代理的沉积成分重建白垩纪晚期到古新世的二氧化碳水平

• 批准号: 2308272
• 负责人: Kelsey Doiron
• 金额: $ 33.37万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-10-01 至 2025-09-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2308272&HistoricalAwards=false
• 关键词: Postdoctoral; Fellowship; OCE; PRF; Reconstructing

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.

该项目的重点是重建古代大气中的二氧化碳水平，提供有关过去“温室”条件的关键证据，这对预测和模拟地球未来气候至关重要。这个项目研究的是从保存在海洋沉积物中的古代生物中提取的有机分子。这些分子的组成记录了环境信息，其中包括二氧化碳水平的证据，从而能够通过地质历史估计其大气丰度。这项研究的重点是对2022年国际海洋发现计划(IODP)第392次远征期间从南非海岸外的特兰斯凯盆地发现的沉积物岩芯中的分子进行检查。这些沉积物是在7900万到6100万年前沉积的，当时的二氧化碳水平比今天高得多，但也在上升，所以这个时间间隔提供了对地球未来气候的类比。因此，该项目将促进我们对过去二氧化碳水平的了解，并寻求改进和扩大用于测定二氧化碳水平的方法。它还包括旨在扩大科学参与的倡议。Pi-DoIron将通过与南加州Centralia小学学区的合作，吸引K-6年级的学生，并与南非同事合作，创建与IODP 392远征调查结果相关的K-12外联材料。DoIron和她的导师还将领导一个研讨会，讨论已被证明对重建过去气候有用的分子和同位素数据的范围，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。具体地说，该研究项目将通过检查植烷、Pristane、烯酮和甘油二烷基甘油四醚(GDGTS)的del13C值，评估不同脂肪生物标记物类别作为二氧化碳替代品的比较效用。植烷是一种与浮游植物相关的二氧化碳替代物，主要代表叶绿素a的植物素侧链，因此记录了光合作用过程中并入生物量的二氧化碳。然而，由于植烷有可能来自其他来源并实现不同的生化功能，因此在沉积记录中直接应用这种替代品是有关联的。具体地说，古生菌类脂(如二植酸乙酯)可以促进植烷库，从而影响植烷PCO2信号。这项建议试图通过从未成熟沉积物中的其他来源特定的生物标志物获得多个二氧化碳分压记录来检查植烷替代物的准确性。它将评估和比较以下成分：(I)植烷，来自浮游植物叶绿素或古生菌二醚的分解；(Ii)C37烯酮，是浮游植物藻类的特定来源脂类；(Iii)Pristane，是从叶绿素a的植基侧链或生育酚形成的分解产物；以及(Iv)GDGTs，是古生物的膜脂。它将重点研究从IODP 392探险中发现的特兰斯凯盆地的坎帕尼亚到古新世沉积。总而言之，这项研究可以为加强基于不同生物标志物的二氧化碳替代物的应用做出关键贡献，并为晚白垩世至古新世的二氧化碳浓度产生证据，那里的数据稀少，但与未来的气候情景直接相关。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。