PALEOGENE DESERTIFICATION OF CENTRAL ASIA SEEN THROUGH THE PALEOSOL RECORD: A TALE OF CLUMPED ISOTOPES AND SOIL PALEOBAROMETRY
While pCO2 decreases about twofold through the late Eocene and early Oligocene, our results show that soil productivity in NE Tibet decreases by a factor of ten. Soil productivity shows a fast decline starting around 37 Ma and reaching the (low) productivity of modern central Asian deserts at the 34 Ma Eocene-Oligocene transition. Soil temperatures decrease abruptly at the Eocene-Oligocene Transition, but recover after the Oi-1 glaciation, returning to their greenhouse Eocene values. However, soil productivity never recovers, indicating the permanent set-up of desert conditions. Our results thus indicate that if the uplift of the Tibetan Plateau and the retreat of the Paratethys might have paved the way to aridification in NE Tibet, final desertification was triggered by global cooling. Our findings also have important implications for the use of soil paleobarometers, which commonly consider soil productivity as a constant through past intervals of pCO2 change. We show here that soil productivity can be extremely sensitive directly or indirectly to pCO2 changes and suggest that paleo-pCO2 reconstructions based on soil properties are significantly biased by these effects.