Environmental and Climatic Change Across the Paleocene-Eocene Boundary in the Continental Interior of North America

北美大陆内陆古新世-始新世边界的环境和气候变化

• 批准号: 0640076
• 负责人: Jonathan Bloch
• 金额: $ 19.4万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-05-15 至 2011-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0640076&HistoricalAwards=false
• 关键词: Environmental; Climatic; Change; Across; Paleocene

This project investigates how vegetation structure responded to global warming of 5-10 C and increased atmospheric CO2 during the Paleocene-Eocene Thermal Maximum (PETM, approximately 55.8 million years ago), and whether this in turn affected the fauna feeding on this vegetation. Canopy structure in the PETM has important implications for the dispersal and subsequent evolution of the earliest representatives of several modern mammalian clades. Three dimensional vegetation structure is important for many reasons. It affects the albedo of land surfaces, hydrologic cycling, atmospheric circulation near the earth's surface, and carbon storage. All of these affect climate and biogeochemical cycles on a global scale. Vegetation also forms the habitat in which terrestrial organisms move and acquire food, and it fundamentally influences their locomotor adaptations and diet. This project tests the hypothesis that vegetation structure changed from open- to closed-canopy forests during the PETM. This has important implications for the global dispersal and ensuing radiations of the oldest known true primates (Euprimates), perissodactyls (odd-toed ungulates), and artiodactyls (even-toed ungulates), which first appeared in North America during the PETM. The earliest euprimates were highly specialized arborealists and their dispersal may have been facilitated by the development of a closed canopy. Vegetation growing in the understory of closed canopy forests has lower 13C/12C ratios than vegetation growing in open environments. Mammals that consume understory vegetation record this 'canopy-effect' in their mineralized tissues (like teeth). This project infers canopy structure by analyzing stable carbon isotope ratios (13C/12C) in mammalian tooth enamel. Fossil teeth are sampled for ~16 species from intervals before, during, and after the PETM. The teeth come from the southeastern Bighorn Basin (SBB) where the PETM is constrained biostratigraphically and geochemically by a carbon isotope excursion. This area contains the only macrofloras known from the PETM, which aids paleoenvironmental and paleoclimatic interpretations. The project also samples teeth and bone in extant mammalian faunas from the Neotropics to better constrain isotopic parameters that are used to interpret canopy structure and resource partitioning. The canopy effect is well documented in Old World faunas, especially from Africa, but is poorly constrained in Neotropical faunas. However, faunas in the late Paleocene and PETM may have been more analogous to modern Neotropical faunas, in that they lacked obligate folivores, which could diminish the canopy effect and narrow the range of faunal isotopic variability. Thus, study of Neotropical faunas should strengthen interpretations.Broader impacts include the training of undergraduate students in field and laboratory techniques, and in database creation, management, and web interface. Project results will be broadly disseminated through professional meetings, publications, the FLMNH website on-line searchable database, and public lectures. Study of environmental change during the PETM may ultimately be useful for predicting the long-term consequences of global warming and is of growing interest to policy makers and the public.

该项目研究了古新世 - 纽热最大值（PETM，大约5580万年前），植被结构如何响应5-10 C的全球变暖，并增加了大气中的二氧化碳，以及这是否影响了对这种植被的动物群。 PETM中的冠层结构对几个现代哺乳动物进化枝的最早代表的分散和后续演变具有重要意义。由于许多原因，三维植被结构很重要。它影响着土地表面的反照率，水文循环，地球表面附近的大气循环以及碳储存。所有这些都会在全球范围内影响气候和生物地球化学周期。植被也形成了陆地生物移动和获取食物的栖息地，它从根本上影响了它们的运动适应和饮食。该项目检验了以下假设：植被结构在PETM期间从开放式植物森林转变为封闭式森林。这对最古老的已知真实灵长类动物（Euuprimates），Perissodactyls（奇异的无凝结物）和Artiodactyls（甚至是脚趾的无凝结物）的全球散布和随之而来的辐射具有重要意义，该乳酸（甚至是脚趾脱落的）在PETM期间首次出现在北美。最早的辅助剂是高度专业的树木植物，它们的扩散可能是通过封闭的树冠的发展来促进的。在封闭的树冠林的植被中生长的植被比在开放环境中生长的植被的比率低13c/12c。消费林木的哺乳动物记录了其矿化组织中这种“树冠效应”（如牙齿）。该项目通过分析哺乳动物牙釉质中稳定的碳同位素比（13c/12c）来渗透冠层结构。在PETM之前，期间和之后，将化石牙齿从〜16种采样。牙齿来自东南大角盆地（SBB），其中PETM受到碳同位素偏移的生物地层和地球化学的约束。该区域包含PETM已知的唯一大型植物，该大紫外线有助于古环境和古气候解释。该项目还将现有的哺乳动物动物群中的牙齿和骨头从新光学采样，以更好地约束用于解释冠层结构和资源分配的同位素参数。冠层效应在旧世界动物群中有充分的文献记载，尤其是来自非洲的动物区系，但在新热带动物区系受到限制。但是，古新世晚期和PETM中的动物群可能与现代的新热带动物动物群更类似，因为它们缺乏专有的叶子，这可能会减少冠层效应并缩小动物的同位素变异性范围。因此，对新热带动物区系的研究应加强解释。Broader的影响包括对现场和实验室技术的本科生的培训，以及在数据库创建，管理和Web界面中的培训。项目结果将通过专业会议，出版物，FLMNH网站在线搜索数据库和公开演讲来广泛传播。对PETM期间环境变化的研究最终可能有助于预测全球变暖的长期后果，并且对政策制定者和公众产生了越来越多的兴趣。