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

智力优势：PI建议从富含有机质的沉积岩中获得高分辨率的痕量金属地球化学剖面，以研究太古宙晚期至中元古代气候和生物圈氧化作用的演化。气候和氧气之间的联系是多方面的。深海中的氧气水平受到有机碳从生产性地表水域输出的速度的影响，因此最终来自大气中的二氧化碳。反过来，加强海洋沉积物中有机碳的埋藏可以增加大气中的O2含量，从而对依赖CH4作为温室气体的太古宙地球造成气候后果。氧气水平还影响海洋中铁和钼等微量营养物质的浓度，潜在地改变海洋表面生物群的活力和从表层到深层的碳泵效率。PI的早期工作发现了氧气光合作用和海洋表面氧合作用的痕迹，至少50-100英里。在大气O2首次大幅上升之前(2.45-2.32Ga大氧化事件；GOE)。他们的化学地层学方法揭示了一段原本未被认识到的生物圈氧合历史，这一历史比之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气、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相同基本概念能解释太古宙和元古界的条件吗？PIS建议通过编制晚太古代至中元古代岩石痕量金属浓度的广泛汇编来完善生物圈氧化的时间线，重点是横跨GOE的关键区间：2.7Ga喜悦湖层序(美国明尼苏达州)，2.3Ga Rooihoogte和Timeball Hill地层(南非)，1.8Ga-1.7Ga船岭沟组(中国北部)。痕量金属地球化学剖面与沉积铁地球化学相结合，可以制约局部沉积条件的性质(如底水氧化还原状态和盆地制约)。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和海水中的Mo/TOC进行比较，可以估计古代海洋中的底层水Mo含量。对于海洋地球化学了解较少的其他痕量金属，可以通过与钼进行比较，得出不同时间间隔之间金属海洋收支的较大差异。钼同位素古氧化还原替代物将被用来获得对区域/全球水柱Euxinia范围的独立限制，并评估对海水中痕量金属丰度的影响。Re-Os年代学可以提供准确的沉积年龄。PIS将解决四个主要问题：1.普遍存在的表层海洋氧合作用(以及由此推断的造氧光合作用)和GOE之间的时间间隔有多长？2.早期古元古代金属海洋预算对GOE的反应如何？3.金属海洋预算是否显示了中元古代与生物圈O2增加和/或海洋Euxinia扩张有关的时间趋势？4.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受到了怎样的影响？更广泛的影响：这一建议促进了Co-Pi Kendall的早期职业发展。此外，作为其项目活动的一部分，私人投资机构计划建立一个试点项目，为亚利桑那州立大学有肢体残疾(即视力、听力、言语或运动障碍)的本科生提供实验室研究经验。试点的最终目标是增加残疾大专学生进入科学实验室的机会。它还将利用肯德尔作为一名成功的年轻实验室科学家的经验，他患有严重的听力和轻微的言语障碍。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。刚果民主共和国将提供课堂辅助设备和辅助技术，以促进学生直接参与实验室研究活动，包括样品准备、分析、数据整理和本科生论文准备。

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.