Impact of Paratethys sea on Eocene Central Asian seasonality: from climatic model to bivalves high-resolution geochemistry

Abstract:

The modern Asian climate is mainly characterized by a monsoonal duality between humid summers in southern and eastern Asia and arid climate in Central Asia resulting in a strong seasonality in terms of precipitation and temperature in these respective regions. Asian Monsoons are also characterised by the aridification in Central Asia due to the foehn effect north of the Tibetan Plateau and the inherent perturbation of the atmospheric circulation generated by the monsoons. According to climate models, Asian Monsoons have been mainly governed by Tibetan plateau uplift, the retreat of a vast epicontinental sea (the Proto-Paratethys sea) and global climate changes. Evidence for monsoons a old as Eocene are starting to be established by proxy and model data. This corresponds to the timing of the Proto-Paratethys retreat, however, the role of this sea on climate and the monsoonal expression in that period remain to be established. Here we show, using infra-annual geochemical proxies from oyster shells of the Proto-Paratethys sea and climate simulations, that the Central Asian region was generally arid with high seasonality from hot and arid summers to wetter winters. This high seasonality in Central Asia therefore supports an intense monsoonal circulation was already established although the climate pattern was significantly different than today. During winter months, a strong influence of the Proto-Paratethys moisture is indicated by enhanced precipitations as well as modelled stable isotopic composition of precipitation significantly higher than today. This supports a strong influence on local climate of the Proto-Paratethys sea, which subsequently retreated and was replaced by the Pamir mountains. During Eocene summers, the local climate was more arid despite the presence of the Proto-Paratethys. This may be explained by a strong anticyclonic Hadley cell descending at these latitudes (25 to 45 N) over Central Asia during Eocene times. Furthermore, the Tibetan plateau emerging to the south may have generated a strong Foehn effect during summer months bringing warm and dry air in Central Asia.