Résumé
Climate models suggest that the onset of Asian monsoons and aridification have been governed by Tibetan plateauuplift, global climate changes and the retreat to the west of the vast epicontinental Proto-Paratethys sea duringthe warm Eocene greenhouse period (55-34 million years ago). However, the role of the Proto-Paratethys seaon climate remains to be quantified by accurate and precise reconstructions. By applying a novel intra-annualgeochemical multi-proxy methodology on Eocene oyster shells of the Proto-Paratethys sea and comparing resultsto climate simulations and sedimentology analyses, we show that the Central Asian region was generally arid witha high seasonal contrast characterized by hot and arid summers and wetter winters.Hotter and more arid summers despite the presence of the Proto-Paratethys may be explained by warmerEocene global conditions with a strong anticyclonic Hadley cell descending at Central Asian latitudes and astronger Foehn effect from the emerging Tibetan Plateau to the south. This implies that the shallow sea did nothave a strong dampening thermal effect on the monsoonal circulation in contrast to previous circulation modelsresults but in agreement with recent evidence for Eocene summer monsoons.Enhanced winter precipitations, relative to modern, is linked to a westerly moisture source coming fromthe Proto-Paratethys sea at that time. Additional bulk sediment stable isotope data from marine limestones andpedogenic carbonates suggest a gradual decrease in this westerly moisture source, which is in line with the retreatof the Proto-Paratethys followed by the Oligo-Miocene orogeny of the Central Asian ranges (Tian Shan andPamir) shielding the westerlies.