Ground-penetrating radar assisted ice core research: The challenge of Alpine glaciers and dielectric ice properties

• Main Author: Bohleber, Pascal
• Format: Thesis
• Language: unknown
• Published: 2011
• Subjects: Monte Rosa; ice core
• Online Access: https://epic.awi.de/id/eprint/25535/; https://epic.awi.de/id/eprint/25535/1/Dissertation_Bohleber_2011.pdf; https://hdl.handle.net/10013/epic.39102; https://hdl.handle.net/10013/epic.39102.d001

Ice cores from Alpine drilling sites may provide long-term climate records. They are more complicated to interpret than their polar counterparts, however. The present thesis investigates the assistance for Alpine ice core research via ground-penetrating radar (GPR). First, the potential for reconstructing atmospheric signals is assessed for stable water isotope records based on a multi-core array at Colle Gnifetti (Monte Rosa, 4450 m asl). Here, a common atmospheric signal is revealed by time series analysis though adequate knowledge of the age-depth distribution is still needed for proper interpretation. Mapping isochronous GPR-reflections allows to consistently link the ice core chronologies up to 80 years before present. This is extended up to 120 years and over the whole drilling area by simple 2.5-dimensional flow modelling. Interpreting GPR-reflections in terms of physical ice core properties crucially relies on the complex dielectric permittivity. Aimed at investigating this material property specifically at radio-frequencies, previously constrained by sparse data only, a coaxial transmission line is adapted for glacier ice. Measurements of pure, artificial and natural ice samples between 1 MHz and 1.5 GHz at –20°C reveal for the permittivity of isotropic ice a real part of 3.16 +/- 0.03. The only signs of dispersion are found below 10 MHz, potentially associated with the high frequency tail of the Debye-dispersion.