23.11.2021 - 17:00
Long‐period astronomical forcing on the strength of Miocene westerlies in Central Asia
The Miocene climate transition (MCT) represents a major global climatic shift towards sustained cooling of our planet. The mechanisms behind this cooling, its regional differentiation and the feedbacks involved are still a matter of debate. Continental settings of Central Asia witnessed increased desertification, but its timing and the interplay between regional and global climatic factors are not well understood. The lecture will provide recent insights about the regional climate evolution and the mechanisms of atmospheric moisture supply towards Central Asia by presenting data from a high-resolution, well-constrained terrestrial record of saline lake deposits spanning the MCT. The 450-m-thick succession exposed in the Aktau section in the Ili Basin, SE Kazakhstan, is representative for a phase of widespread lake formation. Regular depositional cycles representing changes in sedimentary facies and lake level, express a strong sensitivity to moisture availability under arid to semi-arid climate conditions. Time series analysis of climate sensitive geochemical and environmental parameters, together with the determination of absolute rock ages, enabled the identification of sedimentary cycles equivalent to climate influencing variations of the Earth's orbit and tilt angle (405 ka and 1.2 Ma long). These modulations of precession and obliquity affected the regional strength of atmospheric pressure gradients and westerly winds, which in turn was crucial for the magnitude of moisture transport evaporated from the Eastern Paratethys and Mediterranean seas.