Cooling, vegetation shift and decline in monsoonal rainfall in NE Tibet through the greenhouse to icehouse transition

• Main Authors: Dupont-Nivet, Guillaume, Page, Mara, Meijer, Niels, Barbolini, Natasha, Al., Et
• Other Authors: Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Key Laboratory of Orogenic Belts and Crustal Evolution, Peking University Beijing, Institute of Earth and Environmental Science Potsdam, University of Potsdam = Universität Potsdam, University of Washington Seattle, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2019
• Subjects: [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Antarctic; The Antarctic; Antarc*
• Online Access: https://insu.hal.science/insu-02090855

International audience Understanding how and why global climate tipped from greenhouse to icehouse conditions remains a major challenge.This critical shift is well documented in the marine realm characterized by a steady decline in global temperatureuntil a large and rapid cooling step at the Eocene-Oligocene Transition (EOT). However, the chronology andmechanisms of cooling on land remain unclear. To reconstruct Paleogene climate conditions for the Tibetan Plateauand the Asian continental interior, clumped isotope thermometry and palynology in accurately-dated continentalrecords from northeastern Tibet, are here combined with climate and vegetation simulations. Our results show twosuccessive dramatic (>9 C) drops in soil carbonate temperature, at 37 Ma and at 33.5 Ma associated respectivelywith the appearance and dominance of high altitude conifer forests. Such large temperature decreases associatedwith ecological reorganisations cannot result from regional cooling alone. They require shifting of the rainy seasonto cooler months, which we interpret to reflect a decline of monsoonal intensity. Our results suggest that theresponse of Asian temperatures, monsoonal rainfall and vegetation to the decline of atmospheric CO2 and globaltemperature through the late Eocene occurred in two steps separated by a period of climatic instability. Our resultssupport the onset of the Antarctic Circumpolar Current coeval to the Oligocene isotope event 1 (Oi-1) glaciationat 33.5 Ma, reshaping the distribution of surface heat worldwide; however, the origin of the 37 Ma cooling eventremains to be determined.