Tim Liesenhoff

Quantitative climate modeling for MIS 3 in southern Europe based on multi-proxy data of precisely dated speleothems from Perama Cave, Greece

Earth’s climate has undergone major changes in its past, which can be attributed to various environmental influences, such as changes in radiation intensity or the emission of greenhouse gases (i.e. CO2). However, to fully understand the variability of the global climate system, it is important to note that climate change is defined by complex interactions in Earth’s climate cycle, and not only by direct or indirect changes in global mean temperature. As an example, the period of the Pleistocene (2.59 Ma - 11.7 ka) is characterized by an increasing climate variability compared to the current period, the Holocene (11.7 ka - recent). These variations in climate are subdivided into phases called Marine Isotope Stages (MIS), representing the frequently alternating interglacial and glacial phases of the Pleistocene.

The main focus of my project lies on the study of MIS 3 (ca. 57 ka - 27 ka), a warm period characterized by numerous abrupt climate changes. These climate fluctuations were first detected in distinctive isotopic signatures from Greenland ice cores. The majority of these climate changes are so-called Dansgaard-Oeschger events (D/O), which were characterized by rapid (local) warming (rising temperatures up to 16°C in polar regions) followed by a gradual cooling. Other regions of the world were also affected by more or less severe climate change during D/O events, especially the Mediterranean region and southern Europe. The origins of these events are largely unknown and the subject of current paleoclimate research.

With the continuous development of Global Circulation Models (GCMs) over the last decades, climate models were also used successfully in paleoclimate research, in particular to investigate the systematics of past climate changes. Due to the absence of meteorological records from the non-historical past, the quality of paleoclimate modeling depends heavily on the interpretation of isotope proxies, such as stable oxygen isotope ratios of 16O and 18O, which are often measured in speleothems. The incorporation of a diagnostic isotopic submodule (SWI, 2H and 18O) and a precipitation-dripwater-speleothem transition model into the system architecture of GCMs allows to isolate the multitude of different isotopic fractionation effects in the global climate cycle and in the speleothem cave itself, thereby evaluating their influence on stable isotope signatures of analyzed speleothems. With the analysis of different proxy data sets (stable isotopes/trace elements) from speleothems of Perama Cave in north-western Greece in combination with GCM palaeoclimate modeling, it is possible to evaluate simulations based on their agreement with direct proxy observations, and thus to obtain detailed insights into the global climate pattern during MIS 3 and the late Pleistocene.