Collaborative Research: Examining the Evolution of Biospheric Oxygenation in Late Archean to Middle Proterozoic Oceans Through High-Resolution Trace Metal Chemostratigraphy

学术价值：PIs建议从富有机物沉积岩中获得高分辨率的痕量金属地球化学剖面，以研究晚太古宙至中元古代的气候和生物圈氧合演化。气候和氧合之间的联系是多方面的。深海中的氧含量受到有机碳从生产性地表水输出的速率的影响，因此最终来自大气中的二氧化碳。反过来，海洋沉积物中有机碳的增加可以增加大气中的氧含量，对太古代地球的气候影响依赖于甲烷作为温室气体。氧气水平还会影响海洋中微量营养物质（如铁和钼）的浓度，从而潜在地改变海洋表面生物群的活力和表层到深层碳泵的效率。PIs的早期工作发现了氧气光合作用和海洋表面氧化作用的痕迹，至少在大气O2第一次主要上升（2.45-2.32 Ga大氧化事件；GOE）之前50-100万年。他们的化学地层学方法揭示了生物圈氧合作用的历史，这个历史比以前认识到的要复杂得多。因此，对这段历史的详细调查使他们能够测试与氧、碳、微量营养素和气候有关的基本概念。例如，用来解释全新世气候和碳循环的基本概念能否解释太古代和元古代的条件？PIs建议通过对晚太古代至中元古代岩石的微量金属浓度进行广泛的编辑，以细化生物圈氧合的时间线，强调跨越GOE的关键区间：2.7 Ga Joy Lake层序（美国明尼苏达州），2.3 Ga Rooihoogte组和Timeball Hill组（南非），以及1.8-1.7 Ga川岭沟组（华北）。微量金属地球化学剖面与沉积铁地球化学相结合，可以约束局部沉积条件的性质（如底水氧化还原状态和盆地约束）。通过将这些岩石样品的Mo/TOC与现代缺氧盆地的沉积物Mo/TOC和海水浓度进行比较，可以估计古代海洋底部水的Mo浓度。对于海洋地球化学了解较少的其他痕量金属，可以通过与Mo的比较来确定不同时间间隔的金属海洋收支差异。Mo同位素古氧化还原代理将用于获得区域/全球水柱氧化程度的独立约束，并评估对海水中痕量金属丰度的影响。Re-Os年代学可以提供精确的沉积年代。pi将解决四个主要问题：1。普遍的海洋表面氧化作用（以及由此推断的含氧光合作用）的发展与GOE之间的时间差有多长？2. 早古元古代海洋金属收支对GOE的响应是什么？3. 在中元古代，金属海洋收支是否显示出与生物圈O2增加和/或海洋氧气扩张有关的时间趋势？这种趋势对地球早期的气候有什么影响？微生物和真核生物的生态和进化是如何受到影响的？更广泛的影响：该提案促进了Co-PI Kendall的早期职业发展。此外，作为项目活动的一个组成部分，pi计划建立一个试点项目，为亚利桑那州立大学有身体残疾（即视力、听力、语言或运动障碍）的本科生提供实验室研究经验。该试点项目的最终目标是增加残障大学生进入科学实验室的机会。它还将利用肯德尔作为一名有严重听力和轻度语言障碍的成功的年轻实验室科学家的经验。与亚利桑那州立大学残疾资源中心（DRC）合作，将为每个学生制定具体的计划。DRC将提供课堂辅助和辅助技术，以促进学生直接参与实验室研究活动，包括样品制备，分析，数据简化和准备本科论文。

Intellectual merit: The PIs propose to obtain high-resolution trace metal geochemical profiles from organic-rich sedimentary rocks to examine the evolution of climate and biospheric oxygenation in the Late Archean to Middle Proterozoic. The connections between climate and oxygenation are manifold. Oxygen levels in the deep sea are affected by the rate at which organic carbon is exported from productive surface waters, and hence ultimately from atmospheric CO2. In turn, enhanced burial of organic carbon in marine sediments can increase the O2 content of the atmosphere, with climatic consequences on an Archean Earth dependent on CH4 as a greenhouse gas. Oxygen levels also affect the ocean concentrations of trace nutrients such as Fe and Mo, potentially altering the vigor of marine surface biota and the efficiency of surface-to-deep carbon pumping. Earlier work by the PIs discovered traces of oxygenic photosynthesis and surface ocean oxygenation at least 50-100 M.y. before the first major rise of atmospheric O2 (2.45-2.32 Ga Great Oxidation Event; GOE). Their chemostratigraphic approach revealed an otherwise unrecognized history of biospheric oxygenation that is more complex than previously realized. Therefore, detailed investigation of this history allows them to test fundamental concepts that relate O2, carbon, micronutrients and climate. For example, can the same basic concepts developed to explain Holocene climate and carbon cycling explain conditions in the Archean and Proterozoic? The PIs propose to refine the timeline of biospheric oxygenation by developing an extensive compilation of trace metal concentrations for Late Archean to Middle Proterozoic rocks emphasizing key intervals straddling the GOE: the 2.7 Ga Joy Lake Sequence (Minnesota, U.S.A.), the 2.3 Ga Rooihoogte and Timeball Hill Formations (South Africa), and the 1.8-1.7 Ga Chuanlinggou Formation (North China). Trace metal geochemical profiles, when combined with sedimentary Fe geochemistry, can constrain the nature of local sedimentary conditions (e.g., bottom water redox state and basin restriction). Bottom water Mo concentrations in ancient oceans can be estimated by comparing Mo/TOC of these rock samples with sediment Mo/TOC and seawater concentrations in modern anoxic basins. For other trace metals whose marine geochemistry is less well understood, broad differences in metal marine budgets between time intervals can be made by comparison with Mo. The Mo isotope paleoredox proxy will be used to procure independent constraints on the extent of regional/global water column euxinia and assess the impact on trace metal abundances in seawater. Re-Os geochronology may provide precise depositional ages. The PIs will address four main questions: 1. How long is the time lag between the development of pervasive surface ocean oxygenation (and by inference oxygenic photosynthesis) and the GOE? 2. What is the response of early Paleoproterozoic metal marine budgets to the GOE? 3. Do metal marine budgets show temporal trends in the Middle Proterozoic related to increasing biospheric O2 and/or expansion of ocean euxinia?4. What implications do such trends have for climate during the early Earth and how was microbial and eukaryotic ecology and evolution affected?Broader Impact: This proposal promotes the early career development of Co-PI Kendall. Additionally, as a component of their project activities, the PIs plan to establish a pilot project that will provide laboratory research experience for ASU undergraduates with physical disabilities (i.e., vision, hearing, speech, or motor impairments). The ultimate goal of the pilot is to increase access to science laboratories for postsecondary students with disabilities. It will also leverage the experiences of Kendall as a successful young laboratory scientist with severe hearing and mild speech impairments. Specific programs will be crafted for each student in collaboration with the ASU Disability Resource Center (DRC). The DRC will provide classroom aids and assistive technologies to facilitate direct student participation in laboratory research activities, including sample preparation, analysis, data reduction, and preparation of undergraduate theses.