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Rachel Lupien

Assistant Professor

Rachel Lupien


I research the influence of external climate drivers and boundary conditions on regional ecosystems and hydroclimate. I am interested in how human responses to temporal and spatial environmental variations in the past can inform our understanding of the sensitivity of vulnerable regions to modern global warming. My work has focused primarily on Africa, where many regions are highly water- and resource-stressed according to the IPCC, yet the continent is historically under-studied and we lack full understanding of environmental sensitivity to natural and human-induced climate changes. Understanding past climate change and natural oscillations will provide further characterization of vulnerability to a changing world. Additionally, increasingly more hominin fossil and archaeological finds constrain the history of our human ancestors, but comparisons of evolutionary change with the human environment remains poorly understood due to the lack of high-resolution, geochemical climate and vegetation records.

I utilize the novel geochemical proxies of leaf wax biomarker hydrogen and carbon isotopes to quantitatively reproduce past hydroclimate and vegetation. Plants produce waxes to prevent evaporation from and physical damage to their leaves. Leaf waxes are hydrocarbon chains that incorporate a hydrogen isotopic signature from the water they use to photosynthesize, and thus reflect rainfall amount in the tropics. Carbon isotope signatures from the same leaf wax compounds are determined by the plant type, i.e. trees vs. grasses. These geochemical signals of climate are obtained by extracting the leaf waxes from sediment, performing liquid chromatography separations, and running isolated compounds on an isotope ratio mass spectrometer (IRMS) coupled to a gas chromatograph (GC) to measure the hydrogen and carbon isotope ratios. With these paleoclimate records of rainfall and environment, I perform time series and statistical analyses to understand how environments changed and what drove climate through the Oligocene, Miocene, Pliocene, and Pleistocene.

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