Abstract
Abstract. With hundreds of metres of ice, the bedrock underlying Austfonna, the largest icecap on Svalbard, is hard to characterize in terms of topography and physical properties. Ground-penetrating radar (GPR) measurements supply ice thickness estimation, but the data quality is temperature dependent, leading to uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, subglacial bed topography is effectively derived from gravity modelling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight into the basement distribution. This contributes to refining the range of density expected under the ice and improving the subice model. For this study, a prominent magmatic north–south-oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the subsurface lithology, characterized by different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted and adjusted for the potential field interpretation, i.e. magnetic- and gravity-data analysis and modelling. When the results are compared to bed elevation maps previously produced by radio-echo sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves understanding of the geology; assigns physical properties to the basements; and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna, which influence the basal-sliding rates and surges.
Highlights
During the last few decades, with satellite technology advancement and an increased need to understand climate change, the polar regions have become an important laboratory for studying ongoing environmental changes
Along profile B, the poorer fit of the bed topography derived from Ground-penetrating radar (GPR) and radio-echo sounding (RES) with the magnetic and gravity model is caused by the scarcer availability of GPR–RES data
Considering a homogenous basement, the GPR–RES bed topography was corrected with gravity measurements
Summary
During the last few decades, with satellite technology advancement and an increased need to understand climate change, the polar regions have become an important laboratory for studying ongoing environmental changes. The correctness of the resulting topography depends on several glacier parameters, including density, porosity and the water content fraction, which determine the permittivity and, the radio wave velocity used to derive the thickness (Lapazaran et al, 2016). These parameters cannot be directly measured and are highly influenced by temporal and spatial variations of the water content fraction distribution through the glacier (Barrett et al, 2007; Navarro et al, 2009; Jania et al, 2005). Magnetic and gravity modelling were used to assess the feasibility of retrieving topographical and geophysical properties in terms of ice thickness, bed softness, the presence of carbonates and till, and bed topography
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