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

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。Selva Marroquin将启动一个由NSF OCE资助的博士后奖学金，以开发一种新的方法来跟踪海洋沉积物中有机物质的循环。该项目将比较存档的海洋沉积物钻探岩心中共生有机物和含硫矿物(例如黄铁矿或愚人金)中硫的化学成分。硫的埋藏和并入这些不同的形式与海洋系统内碳循环的关键方面密切相关，这些方面是重建所不可或缺的。这项研究的结果将使我们能够更好地了解有关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的悬而未决的问题。这项研究将在加州理工大学与亚历克斯·塞申斯博士和南加州大学的威尔·贝雷尔森博士合作进行。利用这笔资金，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，以帮助小学生建立STEM身份，并扩大他们在该领域的参与。几十年来，人们一直在研究海洋矿物的硫同位素比率(δ34S值)，以帮助重建地球海洋的全球氧化还原历史。一个显著的限制是，黄铁矿的δ34S记录与微生物硫酸盐还原相关的黄铁矿和硫酸盐之间的分馏作用和孔隙水同位素梯度有关，两者都是局部控制的。这项工作的主要目的是通过开发一种新的替代物，基于同时代有机硫(干酪根)和现代海洋沉积物中的黄铁矿之间的δ34S值的差异，来提高我们对δ34S还原记录的理解。关于这一代理的环境控制仍然不清楚，尽管不可否认它与我们寻求重建的海洋系统的关键方面有关(例如，有机碳输送、硫酸盐还原、硫化和碳埋)。为了解决这些不确定性，将对代表各种沉积环境的IODP岩心的样品进行总有机碳、成对干酪根和黄铁矿δ34S以及铁形态的测量。这项工作将有助于确定可变的沉积条件与记录的干酪根和黄铁矿之间的δ34S偏移量之间的关系。这项工作的结果将完善这一代理在地质记录中的应用，这对于提高我们对气候变化将如何影响我们海洋系统的未来的理解是不可或缺的。该奖项反映了NSF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。

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.