CAREER: Deconvolving organic substrates as the critical link between changes in organic matter and global biogeochemical sulfur, carbon, and oxygen cycling

沉积硫同位素记录被用来重建大气中二氧化碳和氧气水平的变化及其对生命和环境的影响。影响硫同位素特征的主要过程是微生物硫酸盐还原，这是海洋沉积物中高达50%的有机物降解的原因，因此在确定通过有机碳埋藏从大气中去除多少二氧化碳方面起着重要作用。该项目将确定当沉积物以植物有机质为主而不是微生物时，微生物发酵产生的简单有机底物如何影响微生物硫酸盐还原速率和硫同位素特征。这些结果将被用来评估种子植物的崛起如何导致生物地球化学硫循环的建立，以及不同类型有机物的混合如何影响现代碳循环。该项目将开展教育活动，培养来自传统上代表性较低的背景、追求科学的高中生对地球科学的热情，并为他们提供参与地球科学研究的机会。该项目将记录有机底物积累速度如何影响平均细胞比减少率，以及它们对硫同位素分馏的影响。该项目将确定在种子植物丰富的沉积物和微生物占主导地位的沉积物中可用于硫酸盐还原的主要有机底物是什么，记录在这些环境中平均细胞比还原速率与硫同位素分馏之间的关系，并使用受沉积包时间分布约束的海洋硫循环的盒子模型来模拟显生界硫循环演变。为期一周的地球科学夏令营将加强对地球科学家如何为解决影响当地社区的环境问题做出贡献的知识，这些学生来自传统上代表性较低的群体，他们将被招募参加为期四周的暑期研究实习。这一奖项反映了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。

The sedimentary sulfur isotope record has been used to reconstruct variations in atmospheric carbon dioxide and oxygen levels and their impact on life and the environment. The main process that impacts sulfur isotope signatures is microbial sulfate reduction, which is responsible for up to 50% of organic matter degradation in marine sediments and therefore plays a major role in determining how much carbon dioxide is removed from the atmosphere via organic carbon burial. This project will determine how the production of simple organic substrates by fermenting microorganisms impacts rates of microbial sulfate reduction and sulfur isotope signatures when sediment is dominated by organic matter from plants versus microorganisms. The results will be used to evaluate how the rise of seed plants lead to the establishment of the “modern” style of biogeochemical sulfur cycling and how mixing of different types of organic matter impacts the modern carbon cycle. The project will conduct educational activities that will build enthusiasm for geoscience in science-motivated high school students from traditionally underrepresented backgrounds and offer them opportunities to get involved with geoscience research.The project will document how rates of organic substrate accumulation affect average cell specific reduction rates and their impact on sulfur isotope fractionations. The project will determine what are the dominant organic substrates available for sulfate reduction in seed plant-rich versus microbially-dominated sediment, document the relationship between average cell specific reduction rates and sulfur isotope fractionations in these settings, and model Phanerozoic sulfur cycle evolution using a box model of the marine sulfur cycle constrained by the time-distribution of sedimentary packages. A one-week Geoscience camp will enhance knowledge of how geoscientists contribute to solving environmental problems that affect local communities in students from traditionally underrepresented groups, who will be recruited for four-week summer research internships.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.