Meteorologische interpretation von depositionen in polaren eisbohrkernen mit hilfe von palaosimulationen des klimamodells ECHAM3

In the present study, the focus was laid on the meteorological interpretation of dust concentrations and snow accumulations as revealed from results of polar ice cores by investigating two paleosimulations of an atmospheric general circulation model. The emphasis was put on the Southern Hemisphere, in particular on the continent of Antarctica. Additionally, results for the Northern Hemisphere are presented. Two different paleosimulations of the Hamburg climate model, ECHAM3 (T42), were used: the timeslice experiments for the Last Glacial Maximum (LGM, 21 kyr BP) and for the Holocene Climate Optimum (HCO, 6 kyr BP). In order to interpret the ice core results, the study is divided into two parts. Firstly, an analysis of the atmospheric branch of the hydrological cycle, with emphasis on moisture fluxes, under the different boundary conditions is presented. Secondly, the results of an isentropic backward trajectory analysis for different polar regions are shown. The model results are validated with ECMWF-analyses. Under recent climate conditions three regions of preferred moisture transports into Antarctica are identified with a high interannual persistence: Dronning Maud Land, Wilkes Land and Marie Byrd Land. The ECHAM3 model shows a good capability of reproducing the observed patterns. In spite of reduced total moisture transports in the climate of the LGM, the relative contribution of the meridional moisture transport in the LGM is increased. This is more pronounced in winter (JJA) than in summer (DJF). Thus the climate of the LGM is characterized by more meridional moisture inflow into Antarctica with a lower interannual variability of the inflow direction, when compared to recent boundary conditions. Similar to present conditions the accumulation in Antarctica reveals higher values in winter than in summer. In comparison to the recent climate the accumulation is reduced by 30% to 50% in the LGM, but the same patterns are observed. The model based accumulation rates fit well with those from ice core data and support the model's capability of paleosimulations. For further interpretation of the results from ice cores, a trajectory analysis was carried out. For extreme periods of moisture accumulation the results reveal longer transport paths in the LGM (higher wind speed) with a shift in the source areas to more distant ocean basins. In the Southern Hemisphere winter the percentage of trajectories crossing continental areas increases in comparison to recent climate conditions during the LGM. In particular for those trajectories ending at Wilkes Land or at Marie Byrd Land, the influence of South America is increased. So far, the model simulation seems to suggest that the higher dust concentrations in the LGM can probably be attributed to more meridional, convergent transport patterns in comparison to the recent climate with a more frequent crossing of Southern Hemisphere landmasses, especially South America. The meaning of the modified atmospheric circulation for the transport and deposition of moisture and aerosols in polar regions, especially in Antarctica, is discussed. For both hemispheres and seasons the HCO reveals similar results as for recent climate conditions.