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

智力优点：PI建议从富含有机物的沉积岩中获得高分辨率的微量金属地球化学剖面，以研究晚太古代至中元古代的气候和生物圈氧合的演变。气候和氧气之间的联系是多方面的。深海中的含氧量受有机碳从生产性表层沃茨中输出的速度以及最终从大气中的CO2中输出的速度的影响。反过来，海洋沉积物中有机碳的强化埋藏可以增加大气中的O2含量，对依赖甲烷作为温室气体的太古代地球产生气候影响。氧气水平也会影响海洋中微量营养素的浓度，如铁和钼，可能会改变海洋表面生物群的活力和从表面到深处的碳泵的效率。PI的早期工作发现了至少50-100 M.y.的产氧光合作用和海洋表面氧化的痕迹。在大气O2第一次大幅度上升之前（2.45-2.32 Ga大氧化事件; GOE）。他们的化学地层学方法揭示了一个原本未被认识到的生物圈氧化历史，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O2，碳，微量营养素和气候相关的基本概念。例如，用来解释全新世气候和碳循环的相同基本概念能否解释太古代和元古代的条件？PI建议通过对晚太古代至中元古代岩石的痕量金属浓度进行广泛汇编，以细化生物圈氧合的时间轴，重点是跨越GOE的关键间隔：2.7 Ga Joy Lake层序（美国明尼苏达州），2.3Ga的Rooihoogte组和Timeball Hill组（南非）和1.8- 1.7Ga的川岭沟组（华北）。微量金属地球化学剖面，当与沉积Fe地球化学结合时，可以限制当地沉积条件的性质（例如，底层水氧化还原状态和盆地制约）。通过比较这些岩石样品的Mo/TOC与沉积物Mo/TOC和现代缺氧盆地的海水浓度，可以估算古海洋底层水Mo浓度。对于海洋地球化学不太了解的其他微量金属，通过与Mo进行比较，可以得出不同时间间隔的金属海洋收支存在很大差异。Mo同位素古氧化还原代理将被用来获得独立的限制区域/全球水柱euxinia的程度，并评估海水中微量金属丰度的影响。Re-Os年代学可提供精确的沉积年龄。PI将解决四个主要问题：1。从普遍的海洋表面氧合（以及由此推断的生氧光合作用）的发展到GOE的发生之间的时间差有多长？2.古元古代早期海洋金属收支对GOE的响应是什么？3.金属海洋预算显示时间趋势，在中元古代有关增加生物圈O2和/或海洋euxinia扩张？4.这些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，作为项目活动的一部分，PI计划建立一个试点项目，为ASU的身体残疾本科生提供实验室研究经验（即，视觉、听觉、言语或运动障碍）。该试点项目的最终目标是增加中学后残疾学生进入科学实验室的机会。它还将利用肯德尔的经验，作为一个成功的年轻实验室科学家与严重的听力和轻度言语障碍。将与ASU残疾资源中心（DRC）合作为每个学生制定具体计划。DRC将提供课堂辅助工具和辅助技术，以促进学生直接参与实验室研究活动，包括样品制备，分析，数据简化和本科论文的准备。

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.