Reconstructing Cretaceous Mean Climate and Seasonality using the Clumped Isotope Paleothermometer on Mollusks

在白垩纪时期(距今66-1.44亿年前)，大气二氧化碳(CO2)水平升高，全球气温比今天更高，特别是在高纬度地区。目前的重建在这段时间内变暖的幅度和空间模式上都存在分歧。该奖项支持一位博士后研究员，他提议使用被称为碳酸盐块同位素古测温的新替代方法，为这一区间开发新的温度估计值，以帮助解开白垩纪气候之谜，这是了解地球对二氧化碳水平上升的反应的关键。这位研究员将在密歇根大学地球与环境科学系的凯格·C·罗曼和克里斯托弗·J·鲍尔森教授的指导下，在两年的时间里进行她的研究。她还计划在稳定同位素实验室指导研究生和本科生研究助理，并参加该部门的地球营，这是一个针对未被充分代表的高中生的项目。这位研究员将尝试使用碳酸盐块状同位素古测温法来绘制第一张古空间地图。这项研究可以为白垩纪的水文循环和海洋动力学提供关键的见解。这项工作产生的对白垩纪的直接约束将改进使用传统方法进行的温度估计，并将展示块状同位素在校准其他替代方法方面的能力。除了温度外，碳酸盐束同位素古测温法还具有重建过去海水的同位素组成的能力。在大空间尺度上测量古地平线可能会揭示过去全球环流的差异，并向我们提供有关过去海洋动力学的信息。拟议的研究包括：1)产生描述白垩纪气候的新的温度和季节性数据，这是高二氧化碳世界的一个例子；2)直接测量一定纬度范围内海水的同位素组成，这可以检验目前关于无冰世界中18Osw空间格局的假设，并为未来的研究提供基础，需要过去的18Osw值；3)比较18Osw；18Osw(一个与盐度高度相关的数值)在海洋盆地内部和之间，可能揭示关于白垩纪期间全球海洋环流模式的信息。PI还将作为少数族裔本科生和少数族裔高中生的导师，并直接让他们参与拟议的研究。参与对社会具有重要意义的真实研究，是提高所有学生在STEM领域坚持不懈的有效方法，但对少数族裔学生尤其重要。这将是对努力扩大科学参与度的重要贡献。

During the Cretaceous period (66-144 Million Years before present), atmospheric Carbon Dioxide (CO2) levels were elevated and global temperatures were warmer than today, in particular at high latitudes. Current reconstructions disagree on both the magnitude and spatial pattern of the warming during this period. This award supports a Postdoctoral Research Fellow who proposes to develop new temperature estimates for this interval - using the novel proxy method known as carbonate clumped isotope paleothermometry - in order to help resolve the enigma of climate during the Cretaceous, which is a key to understanding the Earth's response to increasing CO2 levels. The Fellow will conduct her research over a two-year period under the mentorship of Professors Kyger C. Lohmann and Christopher J. Poulsen in the Earth & Environmental Sciences Department at the University of Michigan. She also plans to mentor both graduate students and undergraduate research assistants in the Stable Isotope Laboratory and to participate in the department's EARTH CAMP, a program for underrepresented high school students. The Fellow will attempt to use carbonate clumped isotope paleothermometry to produce the first spatial map of paleo-δ18Osw. This research could provide key insights into both the hydrological cycle and ocean dynamics during the Cretaceous. The direct constraints on Cretaceous δ18Osw produced by this work will improve temperature estimates made using traditional methods, and will demonstrate the power of clumped isotopes to calibrate other proxy methods. In addition to temperature, carbonate clumped isotope paleothermometry has the ability to reconstruct the isotopic composition of seawater (δ18Osw) in the past. Measurements of paleo-δ18Osw over a large spatial scale may reveal differences in global circulation in the past and inform us about past ocean dynamics. The proposed research includes: 1) production of new temperature and seasonality data describing Cretaceous climate, an example of a high-CO2 world; 2) direct measurement of the isotopic composition of seawater (δ18Osw) across a range of latitudes that can test current assumptions about δ18Osw spatial patterns in an ice-free world and provide a basis for future studies requiring past δ18Osw values; 3) comparison of δ18Osw (a quantity highly correlated with salinity) within and between ocean basins, potentially revealing information about global ocean circulation patterns during the Cretaceous.The PI will also serve as a mentor to minority undergraduates and to minority high school students and involve them directly in the proposed research. Engagement in authentic research that is of importance to society is a proven way to increase persistence in STEM fields for all students, but is particularly important for minority students. This will be an important contribution to efforts to broaden participation in science.