Neogene grassland expansion and climatic evolution

Our group works on the expansion of grasslands in the Cenozoic.  Most recently, Tyler Kukla (PhD 2021) showed that grasslands expanded because of the change in seasonality of precipitation in the late Neogene. His research published in 2022 in AGU Advances used oxygen isotopes of clay minerals and carbonate in paleosols to show that grasslands replaced forests due to the onset of drier winters.  Our earlier work on grasslands focused on the hydrologic budget as well. Evapotranspiration is one of the most significant inputs in the terrestrial hydrologic budget. ET rates, however, vary greatly between vegetation types. Paleoenvironmental changes, such as the rise of grass-dominated ecosystems during the Neogene, would dramatically affect vapor recycling and ultimately drive changes in the hydrologic regime. We are applying several techniques to examining the relationship between changes in vegetation cover and concurrent climate change: 1) Stable isotopic paleoclimate records from sedimentary basins around the world. 2) Simple moisture transport models to assess the isotopic effects of changing vegetation. 3) Isotope-tracking general circulation modeling to improve our understanding of these interactions between the biosphere and the climate system. See our most recent papers in Earth and Planetary Science Letters (Mix et al., 2013) and Global Biogeochemical Cycles (Chamberlain et al., 2014).