Collaborative Research: Oxidant Isotopic Fractionation during Early Diagenesis in Marine Sediments

为了利用O2或氮气进行各自海洋旋回的现代或古同位素研究，我们必须了解它们在沉积消耗过程中的分馏作用，并在可能的情况下确定其机制。对沉积消耗过程中O2和NO3-同位素的分馏进行了一些估计，结果表明分馏值远小于（接近于零）理论值。由于这些观察只在北太平洋东部进行，那里的生产力很高，中层水含氧量很低，来自华盛顿大学和德克萨斯大学海洋科学研究所的两名研究人员计划进行实验室方法开发和现场实验练习，以解决两个问题。第一个问题是，在太平洋西北大陆边缘的高呼吸性沉积物中，氧消耗和反硝化几乎没有观察到同位素分馏，这是否是陆架和上斜坡沉积物普遍存在的特征。第二个问题是N2的产生和N、O同位素分异的缺乏在多大程度上与代谢还原产物的非生物或微生物介导的再氧化有关。pi将在墨西哥湾开展一项实地计划，以(1)测量在甲板上和现场孵育的沉积物中O2和NO3-以及N2和NH4+等相关物种的氧化同位素分馏；(2)通过添加底物（NO3-、15NO3-、HN4+、15HN4+、有机物和还原性物质）和抑制剂进行甲板岩心操作实验，以阐明同位素分馏的可能机制；(3)通过孔隙水和底栖室测量成岩速率，以帮助阐明分馏或缺乏分馏的过程。

ABSTRACTOCE-0118036In order to use either O2 or nitrogen for current or paleo isotopic studies of their respective marine cycles, it is imperative that we know their fractionation during sedimentary consumption and if possible determine the mechanisms. A few estimates of O2 and NO3- isotope fractionation during sedimentary consumption have been made which showed that fractionation was much less (approaching zero) than the theoretical ones. Because these observations were made only in the eastern North Pacific where productivity is high and mid-water oxygen levels are low, two research investigators from the University of Washington and the University of Texas Marine Science Institute plan to carry out a laboratory methods development and field experimentation exercise to address two questions. Question number one asks whether the near absence of isotopic fractionation observed for both oxygen consumption and denitrification in highly respiring sediments of the Pacific Northwest continental margin a ubiquitous characteristic of shelf and upper slope sediments. The second question asks to what extent N2 production and the lack of N and O isotopic fractionation is related to abiotic or microbially mediated reoxidation of reduced products of metabolism. The PIs will conduct a field program in the Gulf of Mexico to (1) measure oxidant isotopic fractionation of O2 and NO3-, as well as related species such as N2 and NH4+ in incubated sediments, both on deck and in-situ; (2) conduct on-deck core manipulation experiments with added substrates (NO3-, 15NO3-, HN4+, 15HN4+, organic material and reducing substances) and inhibitors to elucidate possible mechanisms of isotopic fractionation and (3) make porewater and benthic chamber measurements of diagenesis rates to help elucidate the processes responsible for fractionation or lack thereof.