Bed topography and subglacial conditions of Denman Glacier, East Antarctica: Insights from magnetotelluric data and interdisciplinary studies.

Understanding the basal conditions of East Antarctica's outlet glaciers is critical for accurately modeling future ice sheet evolution. Denman Glacier, one of the continent's fastest-flowing glaciers, has been identified in bed topography models as occupying the deepest continental trough on Earth, thus potentially acting as a major outlet of the East Antarctic Ice Sheet. In this study, we present the first land-based geophysical transect of Denman Glacier using magnetotelluric (MT) data collected along a profile approximately 50 km upstream from its grounding line. The resulting resistivity model images a continuous resistive feature (~10⁴-10⁵~Ω m) interpreted to be glacial ice. This ice overlies lower resistivity regions (~10-10³~Ω m), interpreted to be unconsolidated sediments and rock. The boundary between the resistive ice and underlying rock aligns closely with radar-constrained trough depths at the glacier's flanks. However, in the center of the glacier, the MT model images a trough depth of 1600±200~m below seal level, more than 1000~m shallower than previously estimated, indicating that the extreme depths predicted by earlier models are not observed. Interpreted crystalline and metasedimentary basement rocks are consistent with magnetic sources depths and wider geological constraints. A strong conductor (~10-10²~Ω m) near the center of the glacier is interpreted as a sedimentary topographic high. Electrically conductive anomalies beneath the glacier, including those at the topographic high, are attributed to saline porewater within till or sedimentary rocks. The inferred geometry, bed topography, and basal water distribution will support more accurate modeling of Denman Glacier's stability and future evolution.