We investigate climate change in the geological and historical past and its impacts on the human habitat as well as past changes in the Earth’s magnetic field. Main foci of our research are particularly rapid climate changes that occurred within a few years or decades. Therefore, we exploit high-resolution terrestrial geo-archives as annually laminated (varved) lake sediments and tree rings. A crucial part of our approach is to date precisely and accurately our archives as main prerequisite for robust reconstructions of changes in the past.
Rapid climate changes in the past are considered natural experiments that enable us to gain deep insights into the causes and dynamics of such changes in order to be better prepared to future developments. Therefore, we use structure and chemical composition of seasonal layers (proxy data) that we calibrate with instrumental observation (monitoring). Our vision is to integrate long time series obtained from our high-resolution geo-archives and instrumental data to assessing present-day changes in a long-term context.
Liu, J., Nowaczyk, N., Frank, U., Arz, H. (2019): Geomagnetic paleosecular variation record spanning from 40 to 20 ka – implications for the Mono Lake excursion from Black Sea sediments. - Earth and Planetary Science Letters, 509, pp. 114-124. | doi:10.1016/j.epsl.2018.12.029
The Mono Lake geomagnetic excursion, characterized by low paleointensity and excursional virtual geomagnetic pole (VGP) positions at about 35 ka, has been cumulatively documented from global sites. However, the geomagnetic field geometry during this short-lived excursion is not conclusively described, since excursional directions are only sporadically reported. A full-vector paleosecular variation (PSV) record between 20 and 40 ka could be reconstructed from seven Black Sea sediment cores. The age models of these cores are based on radiocarbon dating and tephrochronology. Further age constrains were achieved by tuning ice rafted debris (IRD) counts and XRF logs (mainly Ca/Ti ratio) as climate proxies for Dansgaard–Oeschger (D–O) warming events, to the oxygen isotope record from Greenland ice cores (NGRIP). The PSV records of individual Black Sea cores were stacked by using 100-yr bins. At about 34.5 cal. ka BP, the Mono Lake excursion is evidenced in the stacked Black Sea PSV record by both a relative paleointensity (rPI) minimum and directional shifts. Associated VGPs from stacked Black Sea data migrated from Alaska, via the Tibetan Plateau and central Asia, to Greenland, performing a clockwise loop. This agrees with data recorded in the Wilson Creek Formation, USA., and Arctic core PS2644-5 from the Iceland Sea, suggesting a dominant dipole field. On the other hand, the Auckland lava flows, New Zealand, the Summer Lake, USA., and Arctic core ODP-919 yield distinct VGPs located in the central Pacific Ocean due to presumably non-dipole field. Finally, Black Sea sediments younger than the Mono Lake excursion recorded only normal secular variations.