Jeremy Caves, Postdoctoral Researcher, Geological Institute, ETH Zürich
Abstract: Modern climate in Asia is characterized by large-scale monsoonal circulation over India and southern China and vast, exceptionally arid deserts across much of Central Asia. This same area contains some of the highest topography in the world, including the Himalayas, Tibetan Plateau, Tian Shan, and Altai. What factors drove the evolution of hydroclimate in Asia over the Cenozoic remains highly contentious. In this talk, I will use the stable isotopes of oxygen (δ18O) and carbon (δ13C)—as recorded in paleosols and lacustrine sediments—to explore the interaction between uplift, climate, and vegetation in Asia during the past 50 Ma. Oxygen isotopes record large-scale atmospheric circulation and the effect of topography and vegetation on moisture transport; in contrast, carbon isotopes record primary productivity. Together, these isotopic systems demonstrate that (1) large-scale atmospheric circulation over Asia has remained largely unchanged during the Cenozoic, despite large changes in uplift and global climate, and (2) primary productivity has declined in Central Asia during the Neogene. Given the invariance of atmospheric circulation, I attribute this decline in productivity to the interaction of the mid-latitude westerlies with high topography in northern Central Asia and a reduction in CO2 fertilization of vegetation. As a further test of these factors, I will present new data from eastern Kazakhstan and western Mongolia that implicate the westerlies in modulating hydroclimate in Central Asia during the Neogene. I conclude that paleoclimatic changes in Central Asia are more tightly controlled by the mid-latitude westerlies and their interaction with high topography in northern Central Asia than by changes in the height or extent of the Tibetan Plateau.