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”条件的重要证据，这对于预测和模拟地球未来的气候至关重要。该项目研究了来自海洋沉积物中保存的古代生物的有机分子的成分。分子记录了环境信息，证据包括二氧化碳水平，从而可以通过地质历史估算其大气丰度。这项研究的重点是检查从南非海岸特兰斯凯盆地回收的沉积物岩心中的分子，这些沉积物岩心是在第 392 次探险期间收集的。 2022 年国际海洋发现计划 (IODP)。沉积物沉积于 79 至 6100 万年前，当时二氧化碳水平远高于今天，而且还在上升，因此这个时间间隔为地球未来的气候提供了模拟。 PI-Doiron 将增进我们对过去二氧化碳水平的了解，并寻求完善和扩展用于测定的方法。PI-Doiron 将通过与南部 Centralia 小学区合作，吸引 K-6 学生参与。加利福尼亚州并与南非同事合作，制作与 IODP 392 号探险队的发现相关的 K-12 外展材料。Doiron 和她的导师还将主持一个研讨会，讨论已被证明有助于重建过去气候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。具体来说，该研究项目将通过检查 del13C 值来评估不同脂质生物标记物类别作为 pCO2 代理的比较效用植烷、降植烷、烯酮和甘油二烷基甘油四醚 (GDGT) 是一种与浮游植物相关的 pCO2 替代物，主要代表叶绿素 a 的植醇侧链，因此记录了光合作用过程中纳入生物量的 CO2。与在沉积记录中直接应用该替代物相关的警告，因为植烷有可能源自其他物质具体来说，古菌脂质（例如二植烷醚）可能对植烷池有贡献，从而损害植烷 pCO2 信号。该提案旨在通过获取多个 pCO2 记录来检查植烷代理的准确性。未成熟沉积物中的其他来源特定生物标志物将评估和比较以下成分：(i) 植烷，源自分解物。浮游植物叶绿素或来自古菌二醚；(ii) C37 烯酮，它们是附着藻类的来源特异性脂质；(iii) 降植烷，一种由叶绿素 a 的植基侧链或生育酚形成的分解产物；以及 (iv) GDGT ，它们是古细菌中的膜脂，它将重点关注来自特兰斯凯的坎帕尼亚到古新世沉积物。从 IODP 第 392 次远征中恢复的盆地。总之，这项研究可以为加强不同基于生物标记的 pCO2 代理的应用做出重要贡献，并为白垩纪晚期到古新世期间的 pCO2 浓度提供证据，这些数据稀疏但与未来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智力价值和更广泛的影响审查标准进行评估，被认为值得支持。