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. > Presentation (mp4)
16. Dezember 2021 – 17:00 Uhr
Climate variability between the mid-Cretaceous and Eocene hothouses peak-greenhouse intervals
Silke Voigt | Goethe-Universität Frankfurt
The Earth underwent long-term climatic cooling between the mid-Cretaceous and Eocene peak-greenhouse intervals. Globally averaged deep-water temperatures gradually declined by almost 10°C between 72 to 59 Ma and atmospheric CO2 levels were significantly reduced during this time. Although long-term changes in atmospheric CO2 are considered as a result of progressive continental fragmentation, changing rates of oceanic crust production and resulting volcanic degassing, the detailed mechanisms behind the cooling and subsequent major global warming culminating in the late Paleocene to Eocene greenhouse climate are still unknown. This lecture will review this enigmatic period by discussing recent proxy data for changes in ocean temperature, sea level and deep ocean circulation, as well as carbon cycle dynamics and potential silicate weathering feedbacks in the context of plate reorganization with special emphasis on the Atlantic Ocean opening.
> Präsentation (mp4)