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This habilitation thesis includes seven case studies that examine climate variability during the past 3.5 million years from different temporal and spatial perspectives. The main geographical focus is on the climatic events of the of the African and Asian monsoonal system, the North Atlantic as well as the Arctic Ocean. The results of this study are based on marine and terrestrial climate archives obtained by sedimentological and geochemical methods, and subsequently analyzed by various statistical methods.
The results herein presented results provide a picture of the climatic background conditions of past cold and warm periods, the sensitivity of past climatic climate phases in relation to changes in the atmospheric carbon dioxide content, and the tight linkage between the low and high latitude climate system. Based on the results, it is concluded that a warm background climate state strongly influenced and/or partially reversed the linear relationships between individual climate processes that are valid today. Also, the driving force of the low latitudes for climate variability of the high latitudes is emphasized in the present work, which is contrary to the conventional view that the global climate change of the past 3.5 million years was predominantly controlled by the high latitude climate variability. Furthermore, it is found that on long geologic time scales (>1000 years to millions of years), solar irradiance variability due to changes in the Earth-Sun-Moon System may have increased the sensitivity of low and high latitudes to Influenced changes in atmospheric carbon dioxide.
Taken together, these findings provide new insights into the sensitivity of past climate phases and provide new background conditions for numerical models, that predict future climate change.
Alfred Wegeners ideas on continental drift were doubted for several decades until the discovery of polarization changes at the Atlantic seafloor and the seismic catalogs imaging oceanic subduction underneath the continental crust (Wadati-Benioff Zone). It took another 20 years until plate motion could be directly observed and quantified by using space geodesy. Since then, it is unthinkable to do neotectonic research without the use of satellite-based methods.
Thanks to a tremendeous increase of instrumental observations in space and time over the last decades we significantly increased our knowledge on the complexity of the seismic cycle, that is, the interplay of tectonic stress build up and release. Our classical assumption, earthquakes were the only significant phenomena of strain release previously accumulated in a linear fashion, is outdated. We now know that this concept is actually decorated with a wide range of slow and fast processes such as triggered slip, afterslip, post-seismic and visco-elastic relaxation of the lower crust, dynamic pore-pressure changes in the elastic crust, aseismic creep, slow slip events and seismic swarms. On the basis of eleven peer-reviewed papers studies I here present the diversity of crustal deformation processes. Based on time-series analyses of radar imagery and satellited-based positioning data I quantify tectonic surface deformation and use numerical and analytical models and independent geologic and seismologic data to better understand the underlying crustal processes.
The main part of my work focuses on the deformation observed in the Pamir, the Hindu Kush and the Tian Shan that together build the highly active continental collision zone between Northwest-India and Eurasia. Centered around the Sarez earthquake that ruptured the center of the Pamir in 2015 I present diverse examples of crustal deformation phenomena. Driver of the deformation is the Indian indenter, bulldozing into the Pamir, compressing the orogen that then collapses westward into the Tajik depression. A second natural observatory of mine to study tectonic deformation is the oceanic subduction zone in Chile that repeatedly hosts large earthquakes of magnitude 8 and more. These are best to study post-seismic relaxation processes and coupling of large earthquake.
My findings nicely illustrate how complex fashion and how much the different deformation phenomena are coupled in space and time. My publications contribute to the awareness that the classical concept of the seismic cycle needs to be revised, which, in turn, has a large influence in the classical, probabilistic seismic hazard assessment that primarily relies on statistically solid recurrence times.