cm-scale variations of crystal orientation fabric in cold Alpine ice core from Colle Gnifetti as source for englacial seismic reflections

Analysis of the microstructural parameters of ice has been an important part of ice core analyses so far mainly in polar cores in order to obtain information about physical processes (e.g. deformation, recrystallisation) on the micro- and macro-scale within an ice body. More recently the influence of impurities and climatic conditions during snow accumulation on these processes has come into focus. A deeper understanding of how palaeoclimate proxies interact with physical properties of the ice matrix bears relevance for palaeoclimatic interpretations, improved geophysical measurement techniques and the furthering of ice dynamical modeling. Variations in microstructural parameters e.g. crystal orientation fabric or grain size can be observed on a scale of hundreds and tens of metres but also on a centimetre scale. The underlying processes are not necessarily the same on all scales. Especially for the short-scale variations many questions remain unanswered. The observed changes in anisotropy resulting from these distinct short-scale variations are deemed strong enough to be the cause of englacial seismic reflections that were recorded during measurements on Colle Gnifetti, Switzerland/Italy, in 2010. Fabric Analyser measurements were conducted on ice samples from different depth ranges of a cold Alpine ice core (72 m length) drilled in 2013 at Colle Gnifetti and located on the earlier seismic profile line. Results were obtained by automatic image processing, providing estimates for grain size distributions and crystal orientation fabric. A first estimate of the causal relationship between the short-scale anisotropy structure and the englacial seismic reflections is presented. The relevance of these results for palaeoclimate reconstruction are discussed