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

为了利用O2或N对它们各自的海洋旋回进行现今或古同位素研究，我们必须知道它们在沉积消耗过程中的分馏情况，并在可能的情况下确定其机制。对沉积消耗过程中O2和NO3-同位素分馏进行了一些估算，结果表明分馏比理论值要小得多(接近于零)。由于这些观测只在生产力高、中水含氧量低的北太平洋东部进行，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呼吸旺盛的沉积物中几乎没有观察到氧气消耗和反硝化作用的同位素分馏，这是否是陆架和上坡沉积物的普遍特征。第二个问题是，氮气的产生和氮氧同位素分馏的缺乏在多大程度上与非生物或微生物介导的代谢还原产物的再氧化有关。PIS将在墨西哥湾实施一项实地计划，以(1)测量甲板和现场孵化沉积物中O2和NO3-以及相关物种(如N2和NH4+)的氧化同位素分馏；(2)在甲板上对添加底物(NO3-、15NO3-、HN4+、15HN4+、有机物和还原物质)和抑制剂进行岩心操纵实验，以阐明同位素分馏的可能机制；以及(3)对成岩速率进行孔隙水和海底小室测量，以帮助阐明导致分馏或缺乏分馏的过程。

ABSTRACTOCE-0117796In 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.