Glaciers are formed from precipitated snow out of the atmosphere. The constituting air masses change their physical and chemical properties along their pathway. Evaporation, biogeochemical processes, volcanic eruptions and the swirl of dust introduce water vapour, reactive trace gases and aerosols into the atmosphere. The measured concentration of chemical impurities, size distribution of aerosols and ratios of stable water isotopes in the snow relate to the just abovementioned processes and are proxy parameters for the state of the bio-geo-sphere at the time the snow is formed. The past snow transforms to glacier ice and at suitable locations in the polar ice sheets it is even stratified, which permits to continuously journey back in time with depth. Distinguished from other climate archives, polar firn additionally entraps old air, which is a unique access to direct samples from the paleo atmosphere.
Another focus in ice core science in AWI is the investigation of physical properties of the drilled material. Especially interesting is the mechanical behaviour as this directly impacts the deformation of ice masses and thus their movement towards the ocean. The most important role here plays the high anisotropy of the mineral ice, which can be measured using the optical anisotropy (polarisation microscopy). Combined with more parameters on the micro-scale, as well as the microstructure mapping of those enables the identification and estimation of the relevant processes (deformation and recrystallisation). Larger traces of deformation can be found in depositional layers (stratigraphy), image with dark field methods in the otherwise transparent ice. The combination of both fields (Palaeoclimate and mechanical properties) is a joint and world-unique Fokus at AWI.
Both, the reconstruction of paleo-climatic records and modelling the evolution of ice sheets ground on a profound understanding of the relevant processes in the ice. Beyond paleo-climatic reconstructions based on the physical and chemical standard parameters we focus our process studies on the densification and air entrapment in polar firn and the influence of microstructures on the deformation properties of the ice. For these studies we complement the set of standard parameters by sophisticated and partly worldwide unique analytical techniques like iceCT, raman spectroscopy and fabric analyser.
The ice sheet up to its entire thickness in the order of few kilometres is directly sampled by drilling ice cores. The abovementioned physical properties along with dielectric profiling are the set of parameters that enable us to link the ice core to the geophysical profiles in their respective vicinity and thus link to the observation of the entire ice sheet.