Bed Topography and Subglacial Conditions of Denman Glacier, East Antarctica: Insights from Magnetotelluric Data and Interdisciplinary Studies.

Abstract 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, potentially acting as a major outlet of the East Antarctic Ice Sheet. Here we present a land‐based magnetotelluric transect across Denman Glacier, acquired approximately 50 km upstream from its grounding line. These measurements provide the first in situ, ground‐based geophysical constraints on the glacier's subglacial structure, enabling evaluation of existing airborne‐derived models and reducing uncertainty and non‐uniqueness in inferred bed topography. The resistivity model images a laterally continuous, highly resistive unit (–), interpreted as glacial ice. This ice overlies lower‐resistivity regions (–) interpreted to be unconsolidated sediments and rock. Along the glacier flanks, the boundary between ice and underlying material aligns closely with radar‐derived trough depths. In contrast, beneath the glacier center, the model indicates a trough depth of m below sea level, more than 1000 m shallower than previous estimates, indicating that the extreme depths predicted by earlier models are not observed. Basement resistivity is consistent with magnetic source depths and regional geological constraints. A low‐resistivity feature () near the center of the glacier is interpreted as a sedimentary topographic high. Low‐resistivity anomalies beneath the glacier are attributed to saline porewater within till or sedimentary rocks. The inferred bed geometry and basal conditions provide improved constraints for modeling Denman Glacier's stability and future evolution.