Assessing Microbial Nitrogen Fixation in Ancient Euxinic Basins

科学依据。古黑色页岩中的有机氮和体态氮以15 N亏损为特征。这可能表明，在海洋盆地有机碳保存增强的时期，由固氮作用推动的生态系统广泛存在。富含有机碳的黑色页岩与氮固定的同位素特征的联系构成了一个悖论：古代海洋中最具生产力的沃茨（至少通过碳保存来衡量）可能缺乏固定氮来为正常的海洋光合作用提供燃料。事实上，海洋深层沃茨中的氧气耗尽会促进微生物通过反硝化和氨氧化去除氮，但也有利于沉积物中磷酸盐的释放。我们假设，显着的固氮，事实上，预计在缺氧的环境中，过量的溶解磷酸盐和低溶解N/P比。 我们试图阐明氮固定在缺氧（缺氧和硫化物）环境中的相对意义，特别是在全球深海氧耗尽（所谓的“海洋缺氧事件”）的时候，我们建议确定氮的同位素特征和相对贡献来自蓝藻在好氧的表面沃茨和光合硫细菌在或低于浅化跃层反映在保存的沉积记录。我们将针对来自古代叶绿素结构和类胡萝卜素色素化合物的生物标志物中的N和C的同位素分析。现代生态系统和文化中色素的同位素和化学研究将形成一个关键的框架，并为我们解释古代签名提供信息。值得注意的是，沉积后叠印（水柱和沉积物成岩作用）可以掩盖散装沉积物氮和有机氮的主要氮同位素特征。地卟啉中氮的分离和分析提供了一种获得古富氧环境中生物质原始氮同位素值的有效方法。（大西洋ODP/DSDP地点，意大利，美国西部内陆），上二叠统（日本和中国）、上泥盆统（NY）和元古宙（AZ）的氮同位素和指示重要微生物群的特定生物标志物化合物。拟议的研究还将需要对现代富氧水柱和沉积物（费耶特维尔-绿湖、纽约和黑海）进行采样和分析，并进行选定的培养实验，以进一步限制卟啉和重要微生物群体细胞生物量之间的相对氮同位素区分。该研究将构成博士学位。为杰米富尔顿和克里斯·朱尼姆写的论文它将促进这些学生在英国约克大学Brendan Keely博士实验室的国际机会。两名本科生暑期实习生将由本项目共同赞助，并由PI指导。支持将提供给现有的和成功的实习计划（目前由IGERT奖资助），为学生提供丰富的经验，在宾夕法尼亚州立大学的地球化学研究。该实习项目在招收少数族裔学生（27.9%）和女生学生（76.7%）方面有着良好的记录，并为所有参与者提供科学、专业和社会指导。目前，富营养化条件促进了美国沿海地区的季节性缺氧或缺氧（例如，长岛海峡、切萨皮克湾、路易斯安那陆架），而且在某些情况下，这些条件正在恶化。因此，初级生产者可获得的氮和磷之间的平衡正在改变，部分原因是沉积物中的磷酸盐释放和反硝化作用伴随着水柱中的低溶解氧浓度（Carpenter和Capone，1998年）。我们提出的关于微生物系统对深时间缺氧发展的反应的研究应该能更好地了解这种生态系统，从而更好地预测未来的影响。

EAR-0525464Scientific Basis. Organic nitrogen and bulk nitrogen in ancient black shales is characteristically depleted in 15N. This could indicate that ecosystems fueled by nitrogen fixation were widespread during times of enhanced organic carbon preservation in ocean basins. The association of organic-carbon rich black shales with this isotopic signature for nitrogen fixation poses a paradox: the most productive waters (at least as measured by carbon preservation) in the ancient ocean were possibly starved for fixed nitrogen to fuel normal ocean photosynthesis. Indeed, oxygen depletion in oceanic deep waters would have facilitated microbial removal of nitrogen by denitrification and ammonia oxidation, yet, also favoring the release of phosphate from sediments. We postulate that significant nitrogen fixation is, in fact, to be expected within oxygen-deficient environments with excess dissolved phosphate and low dissolved N/P ratios. We seek to elucidate the relative significance of nitrogen fixation in euxinic (anoxic and sulfidic)environments, particularly at times of near global deep-sea oxygen depletion (so-called "Oceanic Anoxic Events").We propose to ascertain the isotopic signatures and relative contributions of nitrogen derived from cyanobacteria in oxic surface waters and phototrophic sulfur bacteria at or below shallow chemoclines reflected in preserved sedimentary records. We will target isotopic analyses of N and C in biomarkers derived from ancient chlorophyll structures and carotenoid pigment compounds. Isotopic and chemical studies of pigments in modern ecosystems and cultures will form a critical framework and inform our interpretation of ancient signatures. Notably, postdepositional overprints (water-column and sediment diagenesis) can obscure primary nitrogen isotopic signatures in bulk sediment nitrogen and organic nitrogen. Separation and analysis of the nitrogen in geoporphyins provides a powerful way of obtaining primary nitrogen isotope values for biomass produced in ancient euxinic settings.We will analyze sample suites from Lower and middle Cretaceous (Atlantic ODP/DSDP Sites, Italy, Western Interior US), Upper Permian (Japan and China), Upper Devonian (NY) and Proterozoic (AZ) for nitrogen isotope and specific biomarker compounds indicative of important microbial groups. The proposed research will also require sampling and analysis of modern euxinic water columns and sediments (Fayetteville-Green Lake, NY and the Black Sea) and selected culture experiments in order to further constrain the relative nitrogen isotope discrimination between porphyrins and cell biomass for important microbial groups.Broader Impacts. The proposed research will constitute Ph.D. dissertation work for Jamey Fulton and Chris Junium. It will facilitate international opportunities for these students in the laboratory of Dr. Brendan Keely, at the University of York in Great Britain. Two undergraduate summer interns will be co-sponsored by this project and mentored by the PIs. Support will be provided to an existing and successful internship program (currently funded by an IGERT award) that provides students with rich experiences in biogeochemical research at Penn State. This internship program has a strong track record in recruiting minority (27.9%) and female students (76.7%), and it provides scientific, professional and social mentoring for all participants.Eutrophic conditions currently promote seasonal hypoxia or anoxia in coastal regions of the U.S. (e.g., Long Island Sound, Chesapeake Bay, Louisiana shelf) and, in some cases, these conditions are worsening. As a result, the balance between N and P availability to primary producers is being altered, due in part to phosphate liberation from sediments and denitrification accompanying low dissolved oxygen concentrations in the water column (Carpenter and Capone, 1998). Our proposed research on the response of microbial systems to development of anoxia in deep time should bring a greater understanding of such ecosystems, allowing better predictions to be made for future impacts.