Collaborative Research: The Tropical Temperature History of the Cretaceous Greenhouse Interval Inferred from Tanzanian "Glassy" Foraminifera

合作研究：从坦桑尼亚“玻璃”有孔虫推断白垩纪温室区间的热带温度历史

• 批准号: 0641956
• 负责人: Brian Huber
• 金额: $ 18.83万
• 依托单位: Smithsonian Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-04-15 至 2012-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0641956&HistoricalAwards=false
• 关键词: Collaborative; Research; Tropical; Temperature; History

A wealth of fossil data (terrestrial and marine) from northern and southern high latitudes provide dramatic evidence that the Cretaceous was warm. However, these fossils provide incomplete snapshots of Cretaceous climate as their occurrences are discontinuous and their distributions do not provide a quantitative measure of Earth's temperature. A more continuous history of Earth's temperature change during the Cretaceous can be inferred from delta18-O ratios preserved in the Calcium Carbonate (CaCO3) shells of foraminifera. Unfortunately, interpreting paleotemperatures from delta18-O measurements is complicated by diagenesis and uncertainties regarding the delta18-O composition of contemporary seawater. Discovery of new sites that yield Cretaceous foraminifera with truly exceptional preservation has helped address diagenetic concerns, and parallel analyses of magnesium-calcium (Mg/Ca) ratios can help separate seawater and temperature effects on measured delta18-O values. This proposal requests funds to collect, isolate, and analyze exceptionally well preserved foraminifera from up to 1150 m of Late Cretaceous cores from four key stratigraphic intervals at four localities in coastal Tanzania. Results generated will greatly improve temporal and spatial control of the Cretaceous tropical temperature record. Such improvement is necessary to advance our understanding of the linkages between climate forcing mechanisms, ocean circulation, and patterns of biotic evolution and extinction in the Cretaceous greenhouse world. In combination with climate model experiments, this grant will test hypotheses regarding greenhouse climate dynamics including tropical temperature history, purported greenhouse glacial episodes, and the degree to which tropical and 'global' temperatures co-vary. This project focuses on 1) delta18-O analyses of exceptionally well-preserved foraminifera across Late Cretaceous intervals of extreme warmth and relative cold including glacial intervals, 2) parallel measurements of Mg/Ca in selected samples to help constrain changes in seawater composition, and 3) climate model experiments and data-model comparisons that will allow better evaluation of model sensitivity to Carbon Dioxide (CO2). Broader Impacts: The project involves partners from the United States (Smithsonian Museum of Natural History, University of Missouri-Columbia, and Woods Hole Oceanographic Institution), the United Kingdom (Cardiff University, Bristol University, Southampton University, and University College London), the Republic of Ireland (Trinity College Dublin), and the Tanzania Petroleum Development Corporation. The project has held regular science meetings and has enhanced the involvement of Tanzanian scientists. Graduate and undergraduate students are involved in all phases of this research, and the analyses are done at an NSF-funded stable isotope facility. Local Tanzanians are hired to support many aspects of field work. An additional benefit is improvement in the knowledge of the structural geology and stratigraphy of the southeast coastal region of Tanzania, which is useful for Tanzanian environmental policy decisions including possible hydrocarbon potential and drilling of shallow water wells.

来自北部和南部高纬度地区的大量化石数据（陆地和海洋）提供了白垩纪温暖的有力证据。然而，这些化石提供了白垩纪气候的不完整快照，因为它们的出现是不连续的，并且它们的分布不能提供地球温度的定量测量。从有孔虫碳酸钙 (CaCO3) 壳中保存的 delta18-O 比率可以推断出白垩纪期间地球温度变化的更连续的历史。不幸的是，由于成岩作用和当代海水 delta18-O 成分的不确定性，从 delta18-O 测量值解释古温度变得复杂。发现产生真正保存完好的白垩纪有孔虫的新地点有助于解决成岩作用问题，并且镁钙 (Mg/Ca) 比率的并行分析可以帮助区分海水和温度对测量的 delta18-O 值的影响。该提案要求提供资金，以收集、分离和分析来自坦桑尼亚沿海四个地点的四个关键地层区间高达 1150 m 的晚白垩世岩心中保存异常完好的有孔虫。产生的结果将极大地改善白垩纪热带温度记录的时间和空间控制。这种改进对于增进我们对白垩纪温室世界气候强迫机制、海洋环流以及生物进化和灭绝模式之间联系的理解是必要的。结合气候模型实验，这笔赠款将测试有关温室气候动态的假设，包括热带温度历史、所谓的温室冰川事件以及热带和“全球”温度共同变化的程度。该项目重点关注 1) 对白垩纪晚期极端温暖和相对寒冷区间（包括冰川区间）保存异常完好的有孔虫进行 delta18-O 分析，2) 对选定样本中的 Mg/Ca 进行平行测量，以帮助限制海水成分的变化，以及 3) 气候模型实验和数据模型比较，以便更好地评估模型对二氧化碳的敏感性 （二氧化碳）。更广泛的影响：该项目涉及来自美国（史密森自然历史博物馆、密苏里哥伦比亚大学和伍兹霍尔海洋研究所）、英国（卡迪夫大学、布里斯托大学、南安普顿大学和伦敦大学学院）、爱尔兰共和国（都柏林三一学院）和坦桑尼亚石油开发公司的合作伙伴。该项目定期举行科学会议，并加强了坦桑尼亚科学家的参与。研究生和本科生参与了这项研究的所有阶段，分析是在国家科学基金会资助的稳定同位素设施中完成的。雇用当地坦桑尼亚人来支持实地工作的许多方面。另一个好处是提高了对坦桑尼亚东南沿海地区的构造地质学和地层学的了解，这对于坦桑尼亚的环境政策决策非常有用，包括可能的碳氢化合物潜力和浅水井钻探。