Section 5.2: Climate Dynamics and Landscape Evolution

Rapid climate changes in the past

Velocity and dynamics of climate change still remain elusive. High-resolution geo-archives as annually laminated lake sediments demonstrate that major climate changes occurred within a few years or decades and thus within the timespan of a human generation. We investigate such rapid changes and their impacts on landscapes and ecology in detail and even search for possible early signs indicating such changes. Our research has a focus on the so-called Younger Dryas, the last major climatic change in the northern hemisphere. This cold phase commenced with a sudden cooling ca. 12,700 years ago and ended also abruptly with a rapid warming marking the onset of the Holocene 11,600 years ago, the interglacial that determines our climate until today. The Younger Dryas was accompanied by major reorganizations of atmospheric circulation patterns and lead to large, but regionally different disturbances of landscapes and the environment.

Regional climate change in the past

Distinct regional differences like the particularly strong warming of the polar region (polar amplification) characterize the present global warming. It can be assumed that climate changes in the past have also been regionally different. Detailed knowledge of regional differences associated with climate change is necessary for anticipating impacts of expected future warming in order to develop regional target-orientated adaptation measures. However, only little is known about regional variations of climate change, because the required precise synchronization of geo-archives still is a challenge for dating. We apply novel tephrochronological methods to meet these challenges and synchronize our geo-archives to the precise year.

Hydro-meteorological extremes in times of climate change

An unresolved and controversially discussed problem of climate change is the question if hydro-meteorological extreme events increase as a consequence of global warming. To address this question, we generate flood time series reaching several millennia back in time through the detection and quantification of flood-triggered short-term sedimentation events with microscopic methods. Based on the position of the flood sediments within the regular seasonal deposition pattern we can even determine the season of a flood that occurred several millennia ago. The comparison of these long flood time series with known climatic changes in the past allows us to investigate possible relations between climate change and the frequencies of hydro-meteorological extremes.

Dating and Chronology

Precise and accurate chronologies are crucial for robust reconstruction especially of rapid climate changes in the past. This implies not only the accurate determination of the time of a climate shift, but in particular also the determination of rates of change. We generate such chronologies with a precision of 1% and less for the last 130,000 years for lake sediments through precise counting of annual layers (varve chronology) under the microscope. To synchronize geo-archives from different regions to the precise year we apply novel tephrochronological methods through detecting cryptophra in lake sediments. This allows us to investigate even subtle regional differences in the timing and impacts of past climate changes.

Dendroclimatology

The tree ring archive can provide precisely dated, annually resolved continuous time series. The wide distribution of modern and subfossil trees particularly enables assessment of the temporal and spatial variability of the climate back to the last glaciation (ca.15.000 years ago). Novel techniques of intra-annual quantitative wood cell structure analysis and methods for high throughput and high resolution stable isotope analysis of tree‐rings are utilized and developed further to elucidate seasonal hydroclimatic changes from local to regional scale. Monitoring of climate and stable isotope signal transfer from atmosphere and soil into the tree rings provides climatological, hydrological, and ecophysiological instrumental data for calibration and verification of tree-ring parameters and conversion into proxies. This improves understanding of tree response (adaptation) to recent global change and enhances the quality of palaeoclimate reconstructions from tree rings.