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.

海洋沉积岩是过去地质变化的宝贵档案，记录了有关气候、海平面、营养循环和海洋氧化的信息，这些现象被认为是地球生命历史上许多生物灭绝和起源的基础。研究中心围绕新型地球化学替代物的开发和测试，这些替代物可用于追踪地质历史中的全球变化主题1：海洋铬循环地球化学替代物的开发和测试是在现代环境中进行的，以建立解释性的。指导其地质应用的框架需要额外的研究来检验氧化还原敏感的 Cr(VI) 在海洋中表现出类似营养物的行为的假设，并确定伴随海水 Cr 还原的 Cr 同位素分馏因子。 VI) 和 Cr(III) 的氧化。使用具有真实海洋环流的反演建模工具箱，我们将探索海洋“全球 Cr 阵列”的起源和意义并进行量化。然后，我们将在与过去 5.4 亿年第二次大灭绝相关的全球变化中使用 Cr 同位素。主题 2：全球变化的原因和后果。与赫南特大灭绝有关 最近发表的利用汞替代物的证据表明，赫南特大灭绝发生在火山活动增加的时期，尽管缺乏地质证据表明赫南特大灭绝发生在火山活动增加的时期。火山沉积物释放的二氧化碳使气候变暖，而火山硫气体的排放和加速的大陆风化则使气候变冷。事实上，赫南特灭绝的两次脉冲似乎与大陆冰盖的两次进退有关。我和我的学生、同事将利用一系列传统和新颖的地球化学指标，以特殊的顺序重建围绕两次灭绝的环境变化的详细历史。为了避免沉积地层的全球相关性不精确，我们将在相同的地层剖面上测量所有地球化学指标，以便准确确定全球变化指标的相对时间（地层位置）。灭绝与火山活动引发的全球变化事件有关的假设影响：拟议的研究将填补现代海洋中氧化还原敏感的铬及其同位素行为的重要空白。而所获得的知识将用于建立一个更强大的解释框架来指导地质应用，对赫南蒂斯大规模灭绝事件期间火山活动增加的环境影响进行多代理研究将有助于预测当前化石燃烧造成的未来全球变化。燃料。