Supplementing ice core time series at a small scale Alpine glacier with a 3D full stokes ice flow model using Elmer/Ice

Olaf.Eisen [ at ]


The cold glacier saddle Colle Gnifetti (CG) is the unique drilling site in the European Alps offering ice core records substantially exceeding the instrumental period. In spite of an ice thickness not much exceeding 100 m, CG provides long-term ice core records due to its low net accumulation and rapid layer thinning. However, net accumulation at CG is characterised by strong spatio-temporal variability causing depositional noise and, combined with a complex flow regime, upstream-effects. These intricate glaciological settings hamper the full exploitation of the unique potential for long-term ice core records of this site. Here we present first results from developing a new model attempt, i.e. full stokes with consideration of firn rheology, specifically tailored to the complex CG settings, and utilizing the 3D finite element model Elmer/Ice in combination with existing CG ice core as well as geophysical data. A major objective is to map source trajectories of existing ice core sites in order to evaluate potential upstream effects. Since dating the CG ice cores becomes a challenge already after the last 100 years or so, an additional focus is to assist in finding a reliable age scale, especially targeting depths where annual layers can no more be counted. This includes the calculation of isochronous surfaces for intercomparison of different drilling sites within the CG multi core array. A considerable amount of empirical data has been collected at CG over the last few decades, allowing the model to be established on a solid empirical base. Some of these quantities are used as model input, other of them for validation. Among the input quantities we have a wide range of density and temperature profiles, an over the time surveyed surface topography and a GPR based bedrock topography. Nevertheless especially the measured bedrock topography is not precise enough and limits the model accuracy. Besides that, an important limitation arises also from other not directly measurable model parameters, like the mechanical stress on the glacier boundaries. In order to better constrain them, the input quantities are therefore iteratively tuned such that the measured quantities are reconstructed as good as possible. Here we present first results concerning the reconstruction of some insufficient known model parameters – e.g. the bedrock topography – and concerning the model validation based on comparison with empirical data, i.e. the measured surface velocities and net snow accumulation. Next steps in refining the model are concerned with obtaining better constrained model parameters and boundary conditions comparing the model results with ice core derived data like e.g. the observed layer thinning or the measured vertical age distribution. Another important step is to couple the here presented mechanical model with a thermodynamical one.

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Conference (Talk)
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REKLIM workshop.
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Licciulli, C. , Bohleber, P. , Wagenbach, D. , Eisen, O. , Gagliardini, O. and Hoelzle, M. (2015): Supplementing ice core time series at a small scale Alpine glacier with a 3D full stokes ice flow model using Elmer/Ice , REKLIM workshop .

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