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

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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.