Cr and U isotope perspectives on Earth's oxygenation history informed by studies of their modern cycles

现代循环研究揭示了铬和铀同位素对地球氧合历史的看法

• 批准号: RGPIN-2019-05417
• 负责人: Holmden, Chris
• 金额: $ 2.62万
• 依托单位: University of Saskatchewan
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=738264
• 关键词: Cr; isotope; perspectives; Earth; oxygenation

Marine sedimentary rocks are valuable archives of global-change in the geological past, recording information on climate, sea level, nutrient cycling, and ocean oxygenation. These phenomena are believed to underpin many biological extinctions and originations in the history of life on earth. My research centers around development and testing of novel geochemical proxies that can be used to track global-change in the geological past. Theme 1: Oceanic Cr cycle  Development and testing of geochemical proxies is undertaken in modern environments to build the interpretive frameworks that will guide their geological applications. The emerging Cr isotope proxy requires additional study to test the hypothesis that redox-sensitive Cr(VI) exhibits nutrient-like behavior in the oceans, and to determine Cr isotope fractionation factors accompanying reduction of seawater Cr(VI) and oxidation of Cr(III). Using an inverse modeling toolbox with realistic ocean circulation, we will explore the origin and significance of the oceanic `global Cr array' and quantify input/output Cr-fluxes to and from the oceans. We will then use Cr isotopes in a multiproxy study of global-change associated with the second largest extinction of the past 540 million-years. Theme 2: Causes and consequences of global-change related to the Hirnantian mass extinction  Recently published evidence utilizing the Hg proxy suggests that the Hirnantian mass extinction occurred during a period of increased volcanism, despite the lack of geological evidence for increased volcanic deposits. Volcanic outgassing of carbon dioxide warms the climate, while emissions of volcanic sulfur gases, and accelerated continental weathering, cools the climate. Indeed, two pulses of Hirnantian extinction appear to correlate with two advances and retreats of continental ice sheets, thus indicating a link with major climate change. Using a selection of traditional and novel geochemical proxies, my students, colleagues and I will reconstruct the detailed history of environmental changes surrounding the two extinctions in an exceptional sequence of sedimentary deposits in the Canadian Arctic. To avoid imprecisions in global correlation of sedimentary strata, all geochemical proxies will be measured on the same stratigraphic sections in order to accurately determine the relative timing (stratigraphic position) of global-change indicators. We will test the hypothesis that the extinctions are linked to global-change events triggered by volcanism. Impact: The proposed research will fill important gaps in knowledge regarding the behaviour of redox-sensitive Cr and its isotopes in the modern oceans, while the knowledge gained will be used to build a more robust interpretive framework guiding geological applications. A multiproxy study of the environmental effects of increased volcanism during in the Hirnantian mass extinction event will help to predict future global-change from present-day burning of fossil fuels.

海洋沉积岩是地质过去的全球变化档案，记录有关攀登，海平面，养分循环和海洋氧合的信息。这些现象被认为是地球生命史上许多生物学扩展和起源的基础。我的研究集中在新的地球化学代理的开发和测试中，这些代理可用于跟踪地质过去的全球变化。主题1：海洋CR周期的开发和地球化学代理的测试是在现代环境中进行的，以建立可以指导其地质应用的解释框架。新兴的CR同位素代理需要进行额外的研究，以检验以下假设：氧化还原敏感的CR（VI）在海洋中表现出营养样的行为，并确定发生的CR同位素分馏因子降低了海水CR（VI）和CR（III）的氧化。使用具有逼真的海洋循环的反向建模工具箱，我们将探索海洋“全球CR阵列”的起源和意义，并量化往返海洋的输入/输出CR频率。然后，我们将在与过去5.4亿年的第二大扩展有关的全球变化研究中使用CR同位素。主题2：与临时质量扩展有关的全球变化的原因和后果最近发表了使用HG代理的证据，这表明，尽管缺乏地质证据来增加火山沉积物的地质证据，但在增加火山的时期，hirnantian质量扩展发生。二氧化碳的火山量超过气候，而火山硫气体的排放和加速的连续风化气则冷却气候。实际上，两种额外的延伸脉冲似乎与连续冰盖的两种进步和撤退相关，因此表明了与主要攀爬的主要攀岩联系，我将重建了围绕Sediment的两个延伸序列的环境变化的传统和新颖的地球化学代理，我的学生，同事，我将重建各种环境变化的历史。为了避免在沉积层的全球相关性上即兴，所有地球化学代理将在相同的地层截面上进行测量，以便准确确定全球变化指标的相对时机（地层）。我们将检验以下假设：扩展与火山主义触发的全球变化事件有关。影响：拟议的研究将填补有关氧化还原敏感CR及其在现代海洋中的同位素行为的重要空白，而获得的知识将用于构建更强大的解释性框架指导地质应用。一项多X型研究对亨南特质量扩展事件中火山的环境影响的环境影响将有助于预测化石燃料当今燃烧的未来全球变化。