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

来自北部和南部高纬度地区的大量化石数据（陆地和海洋）提供了白垩纪是温暖的有力证据。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，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δ 18- o比值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，通过delta18-O测量来解释古温度由于成岩作用和当代海水delta18-O组成的不确定性而变得复杂。白垩纪有孔虫的新发现有助于解决成岩问题，镁钙（Mg/Ca）比率的平行分析可以帮助分离海水和温度对测量的delta18-O值的影响。该提案要求资金用于收集、分离和分析保存异常完好的有孔虫，这些有孔虫来自坦桑尼亚沿海四个地方的四个关键地层间隔的晚白垩世岩心，高达1150米。所得结果将大大改善白垩纪热带温度记录的时空控制。这样的改进对于促进我们对气候强迫机制、海洋环流和白垩纪温室世界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，这笔拨款将测试有关温室气候动力学的假设，包括热带温度历史、所谓的温室冰川期，以及热带和“全球”温度共同变化的程度。该项目的重点是1)在白垩纪极端温暖和相对寒冷的时期（包括冰川时期），对保存异常完好的有孔虫进行delta18-O分析；2)在选定样品中平行测量Mg/Ca，以帮助限制海水成分的变化；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（CO2）的敏感性。更广泛的影响：该项目的合作伙伴包括美国（史密森尼自然历史博物馆、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、布里斯托尔大学、南安普敦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。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nsf资助的稳定同位素设施中完成的。当地的坦桑尼亚人被雇用来支持许多方面的实地工作。另一个好处是提高了对坦桑尼亚东南沿海地区构造地质学和地层学的认识，这对坦桑尼亚的环境政策决策很有用，包括可能的碳氢化合物潜力和浅水井的钻探。

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.