Tracking Atmospheric and Vegetation Change Across Cenomanian-Turonian Oceanic Anoxic Event II

该奖项支持一项多学科古植物学和生物地球化学研究，该研究将把中生代海洋缺氧事件（OAE）的海洋和陆地记录联系起来。这些地质上短暂的（600-800 kyr）有机碳埋藏强化期主要发生在白垩纪温室增温高峰时期。有人提出，它们中的一些在碳循环中引起了足够大的扰动，对大气中二氧化碳的影响达到了与冰川尺度振荡相当或更大的水平。然而，大气CO2在OAE之前、期间和之后的历史从未使用陆地二氧化碳分压代用物直接评估过。本项目将研究北美西部内陆盆地Cenomanian-Turonian (C-T, +-94 Ma) OAE II相关的碳生物地球化学循环变化与区域气候变化、植物多样性和生态的区域尺度变化之间的联系。将检验三个主要的相互关联的假设：(1)在OAE II期间，海洋有机碳的产生、埋藏和保存是否作为海洋系统对事件发生前一段时间内大气二氧化碳浓度增加的反馈而开始的？(2)海相碳酸盐和有机碳的显著正同位素偏移表明，海相碳埋藏和保存的增强是否导致了大气二氧化碳的减少？(3) OAE II之前和期间的大气CO2波动是否引起了全球气候变化，进而导致陆生植物群落优势度/多样性结构的景观尺度变化？这些变化在被子植物的兴起中起作用了吗？这些假设将分别通过检测分散植物角质层和大型植物区系的大气古二氧化碳分压（使用孔隙指数-二氧化碳分压代理）和区域平均年温度（使用叶缘分析）的变化速率和幅度进行验证，这些数据主要收集于犹他州西南部达科他和直崖组的边缘海洋剖面。由于陆地剖面与科罗拉多近海海相C-T层型的详细对比，在那里建立了一个高分辨率的时间框架，因此可以确定二氧化碳分压和温度相对于海洋碳埋藏的变化时间。作为该项目的一部分，现代角质层形态的在线档案将用于区分整个C-T区间的分散化石角质层。分散角质层记录的古生态学分析将用于跟踪整个C-T区间区域植被对CO2和气候波动的响应动态。该项目的更广泛影响包括对具有重大社会意义的基础研究（了解碳循环事件与气候变化之间的关系）的科学贡献，培训未来的地球科学家，以及通过创新的教学活动传播成果。该项目的两个关键创新是通过开发角质层和大型植物材料的在线数字数据库对地理信息学的贡献，以及通过周末丰富课程（称为project Excite）吸引地球科学中代表性不足的群体的实质性努力。

This award supports a multidisciplinary paleobotanical and biogeochemical study that will link marine and terrestrial records of a Mesozoic ocean anoxic event (OAE). These geologically brief (600-800 kyr) episodes of enhanced organic carbon burial took place mainly during a time of peak greenhouse warming in the Cretaceous. It has been suggested that some of them caused perturbations in the carbon cycle large enough to impact atmospheric CO2 at levels comparable to, or greater than glacial scale oscillations. Yet the history of atmospheric CO2 before, during, and after an OAE has never been directly evaluated using a terrestrial pCO2 proxy. This project will investigate the links between changes in the biogeochemical cycling of carbon, regional climatic change, and regional scale changes in plant biodiversity and ecology associated with the Cenomanian-Turonian (C-T, +-94 Ma) OAE II in the Western Interior basin of North America. Three main interrelated hypotheses will be tested: (1) was enhanced marine organic carbon production, burial, and preservation during OAE II initiated as a feedback of the marine system to increased concentrations of atmospheric carbon dioxide for a period of time before onset of the event? (2) Did enhanced marine carbon burial and preservation, as indicated by a significant positive isotopic excursion in marine carbonate and organic carbon, result in a draw down of atmospheric carbon dioxide? and (3) Did fluctuations in atmospheric CO2 before and during OAE II cause global climatic shifts which, in turn, resulted in landscape scale shifts in the dominance/diversity structure of terrestrial plant communities? Did these changes play any role in the rise of the angiosperms? These hypotheses will be tested by examining the rate and magnitude of change in atmospheric paleo-pCO2 (using the stomatal index-pCO2 proxy) and regional mean annual temperature (using leaf margin analysis) on dispersed plant cuticle and macrofloras respectively, collected mainly from marginal marine sections of the Dakota and Straight Cliffs Formations of southwestern Utah. Timing the changes in pCO2 and temperature relative to marine carbon burial will be possible due to detailed correlation of the terrestrial sections to the C-T stratotype in offshore marine facies of Colorado, where a high resolution temporal framework has been established. An online archive of modern cuticle morphotypes developed as part of this project will be used to distinguish dispersed fossil cuticles throughout the C-T interval. Paleoecological analyses of the dispersed cuticle record will be used to track regional vegetation dynamics in response to CO2 and climatic fluctuations throughout the C-T interval. The broader impacts of the project include scientific contributions to basic research on a subject of great societal relevance (understanding relationships between carbon cycle events and climate change), training of future geoscientists, and dissemination of results through innovative teaching initiatives. Two key innovations that distinguish the project are a contribution to geoinformatics via development of an online digital database for cuticle and macrofloral material, and a substantive effort to engage under-represented groups in geoscience through weekend enrichment classes (called Project Excite).