ANAMMARKS: ANaerobic AMmonium oxidiation bioMARKers in paleoenvironmentS

在现代海洋环境中，30-50%的氮从海洋中流失是由于厌氧氨氧化（anammox）。这种细菌过程从海洋浮游植物系统中去除一种重要的营养物质氮。因此，厌氧氨氧化对全球海洋初级生产、二氧化碳吸收和碳循环有直接影响。厌氧氨氧化菌只有在低氧到缺氧环境下才有活性，包括水柱中的最低氧区（OMZs）。在当前不断变化的气候下，omz正在扩大，了解这种扩大将如何影响厌氧氨氧化活性，进而影响碳循环是很重要的。在现代和未来气候的类似物中重建古气候使我们能够研究未来的变化将如何影响厌氧氨氧化过程等元素。在地球气候史上有几个例子，扩大的OMZ导致了全面的海洋缺氧。厌氧氨氧化细菌是一种深分支门的成员，在地球历史的关键时期（例如侏罗纪和白垩纪海洋缺氧事件（oae）），厌氧氨氧化过程被认为在创造和维持海洋缺氧方面发挥了重要作用。确定厌氧氨氧化在过去的这些情况中是如何参与的，将有助于更好地预测我们未来可能预期的结果。有机地球化学使用被称为生物标志物的分子化石来研究微生物过程对环境的影响。目前，利用生物标志物对厌氧氨氧化菌进行追踪是利用脂质进行的。然而，生物标志物的适用性有时间限制。例如，无法承受沉积期间和之后发生的降解过程，限制了这些生物标志物的应用时间。虽然梯子烷脂是现代环境的优秀生物标志物，但它们高度不稳定，不适合追踪过去的厌氧氨氧化活性。因此，为了弄清厌氧氨氧化在过去这些极端气候事件中所起的作用，必须首先确定可以在更成熟的沉积物中用作生物标志物的脂质。两种不同的脂类已显示出作为过去厌氧氨氧化生物标志物的潜力，并将在本项目中进行评估。这些脂质将被评估，并将用于追踪过去海洋环境中的厌氧氨氧化。第一类（细菌藿烷多元醇，特别是BHT异构体）似乎适合于最近50 Ma内沉积的沉积物，并且在埋藏后没有暴露于热应力。例如，我们将这些生物标志物应用于秘鲁OMZ下的2 Myr沉积物记录，以探索厌氧氨氧化通过在OMZ增加期间促进氮去除来影响OMZ扩展的假设。第二类（异常环烷烃和支链烷烃）将检测时间窗口扩展到热成熟沉积物中。这些生物标志物将在OAE事件中进行研究，以确定厌氧氨氧化如何影响向固氮的转变，固氮是OAE期间营养吸收的主要途径。此外，这些烷烃将成为石油工业中具有经济效益的项目合作伙伴，在石油工业中，缺氧生物标志物将间接表明有机物和石油的保存潜力。我们将创建一种简化的厌氧氨氧化检测方法，并将其传播给其他地球化学实验室，供他们研究厌氧氨氧化过程。综上所述，这些发现和我们系统研究的结果将有助于通过使用我们已建立的生物标志物来追踪过去的厌氧氨氧化活性，从而了解过去的氮循环。最后，我们的古厌氧氨氧化研究结果将被纳入生物地球化学模型GENIE。这将提高我们对厌氧氨氧化在过去氮循环中所起作用的理解。随后，模型结果将有助于更好地预测在气候变化下厌氧氨氧化对未来氮和碳循环的影响。

In modern marine environment, 30-50% of nitrogen lost from the ocean is due to anaerobic ammonium oxidation (anammox). This bacterial process removes an important nutrient, nitrogen, from the marine phytoplankton system. Thus, anammox has a direct consequence on global marine primary production, the uptake of carbon dioxide, and the carbon cycle. Anammox bacteria performing this process are only active in low-oxygen to anoxic settings, included oxygen minimum zones (OMZs) in the water column. OMZs are expanding in our current changing climate and it is important to understand how this expansion will affect anammox activity and in turn the carbon cycle. Reconstructing paleoclimate in analogs for modern and future climate allows us to study how future changes will affect elements like the anammox processes. There are several instances in Earth's climate history when expanding OMZ has led to full-scale oceanic anoxia. Anammox bacteria are members of a deep-branching phylum, and the process has been hypothesised to have played an important role in creating and maintaining oceanic anoxia during crucial periods of Earth's history (e.g. Jurassic and Cretaceous Oceanic Anoxic Events (OAEs)). Determining how anammox was involved in these past scenarios will help better predict what likely outcomes we can expect in our future.Organic geochemistry uses molecular fossils, called biomarkers, to study the impact microbial processes have had on the environment. Currently, tracing anammox bacteria using biomarkers is done using ladderane lipids. However, the applicability of a biomarker has temporal limitations. For example, the inability to withstand degradative processes, which occur during and after deposition, restricts how far back in time these biomarkers can be applied. Although ladderane lipids are excellent biomarkers for modern environments, they are highly labile and not well suited for tracing past anammox activity. Thus, in order to clarify the role anammox has played during these past extreme climate events, lipids must first be identified that can be used as biomarkers in more mature sediments.Two distinct lipid classes have shown potential as biomarkers for past anammox, and will be assessed in this project. These lipids will be evaluated and will be implemented to trace anammox in past oceanic settings. The first class (bacteriohopanepolyols, specifically BHT isomer) seem suitable for sediments deposited within the last 50 Ma, and that have not been exposed to thermal stresses after burial. For example, we will apply these biomarkers to a 2 Myr sediment record underlying the Peru OMZ to explore the hypothesis that anammox influences the expansion of OMZs by contributing to nitrogen removal during increased OMZ. The second class (unusual cyclic and branched long-chain alkanes) extends the time window of detection into thermally mature sediments. These biomarkers will be investigated in OAE events to determine how anammox influenced a shift towards nitrogen-fixation being the dominate pathway of nutrient uptake during OAEs. Additionally, these alkanes will be economically benefit project partners in the petroleum industry, where biomarkers for anoxia would indirectly indicate preservation potential of organic matter and petroleum. We will create a simplified method for anammox detection that we will disseminate to other geochemistry laboratories for their studies of the anammox process. Combined, these findings and those specifically from our system studies will help understand past nitrogen cycling by using our established biomarkers to trace past anammox activity. Finally, the results of our studies of paleo-anammox will be incorporated into the biogeochemical model GENIE. This will improve our understanding of the role anammox played in past nitrogen cycling. Subsequently, model results will help to better predict the implications of anammox on future nitrogen and carbon cycling under our changing climate.