OCE-PRF-Development of a paired kerogen-pyrite sulfur isotope proxy for organic remineralization

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。Selva Marroquin博士将开始NSF OCE资助的博士后奖学金，以开发一种新方法来跟踪海洋沉积物中有机物的回收。该项目将比较共生有机物和含硫矿物中硫的化学成分（例如，黄铁矿或傻瓜的黄金）在存档的海洋沉积物钻芯。硫以这些不同形式的埋藏和结合与海洋系统内碳循环的关键方面密切相关，这些方面是重建不可或缺的。这项研究的结果将使我们能够更好地了解海洋对与全球气候变化有关的二氧化碳水平上升的化学和生物反应方面的未决问题。这项研究将在加州理工学院与亚历克斯·塞申斯博士和南加州大学的威尔·贝瑞森博士合作进行。有了这笔资金，Marroquin博士将为不同教育水平（即高中和社区大学）的学生提供研究机会和指导，以帮助建立少数民族学生的STEM身份，并扩大他们在该领域的参与。海洋矿物的硫同位素比值（δ 34 S值）已经被研究了几十年，以帮助重建地球海洋的全球氧化还原历史。一个重要的局限性是黄铁矿的δ 34 S记录涉及黄铁矿和硫酸盐之间的分馏，与微生物硫酸盐还原和孔隙水同位素梯度有关，两者都是局部控制因素。本工作的主要目的是通过开发一种新的代用指标来提高我们对还原δ 34 S记录的理解，该代用指标是基于现代海洋沉积物中同时代有机硫（干酪根）和黄铁矿之间δ 34 S值的差异。对这一代理的环境控制仍然不清楚，尽管它与我们寻求重建的海洋系统的关键方面有着不可否认的联系（例如，有机碳输送、硫酸盐还原、硫化和碳埋藏）。为了解决这些不确定性，将对代表各种沉积环境的IODP岩心样品进行TOC、成对干酪根和黄铁矿δ 34 S和Fe形态的测量。这项工作将有助于确定可变的沉积条件与所记录的干酪根和黄铁矿之间的δ 34 S偏移之间的关系。这项工作的结果将完善这一代理在地质记录中的应用，这是提高我们对气候变化将如何影响我们的海洋系统的未来的理解不可或缺的。这个奖项反映了NSF的法定使命，并已被认为是值得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的支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Dr. Selva Marroquin will start an NSF OCE funded Postdoctoral Fellowship to develop a new method to track the recycling of organic matter in ocean sediments. The project will compare the chemical composition of sulfur within co-occurring organic matter and sulfur bearing minerals (e.g., pyrite or fool’s gold) within archived ocean sediment drill cores. The burial and incorporation of sulfur into these different forms is closely tied to key aspects of carbon cycling within the marine system that are integral to reconstruct. The results of this study will allow us to better understand the outstanding questions regarding the chemical and biologic response of the oceans to rising carbon dioxide levels associated with global climate change. The research will be carried out at Caltech with Dr. Alex Sessions in collaboration with Dr. Will Berelson at the University of Southern California. With this funding, Dr. Marroquin will provide research opportunities and mentorship to students at different education levels (i.e. high school and community college) to help build the STEM identities of minoritized students and broaden their participation in the field. The sulfur isotope ratios (δ34S values) of marine minerals have been studied for decades to help reconstruct the global redox history of Earth’s oceans. A significant limitation has been that the δ34S record of pyrite convolves the fractionation between pyrite and sulfate associated with microbial sulfate reduction and the porewater isotopic gradient, both local controls. The primary goal of this work is to improve our understanding of reduced δ34S records by developing a new proxy based on the difference in δ34S values between coeval organic sulfur (kerogen) and pyrite from modern marine sediments. The environmental controls on this proxy remain unclear, though it is undeniably linked to key aspects of the marine system that we seek to reconstruct (e.g., organic carbon delivery, sulfate reduction, sulfurization, and carbon burial). To address these uncertainties, measurements of TOC, paired kerogen and pyrite δ34S, and Fe speciation will be made on samples from IODP cores representing a variety of depositional environments. This work will help determine how the variable depositional conditions correlate with the recorded δ34S offset between kerogen and pyrite. The results of this work will refine this proxy for application in the geologic record which is integral for improving our understanding of how climate change will impact the future of our ocean system.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.