Radar Specularity Content Indicates a Strong Geothermal Heat Flow Gradient in Antarctica's South Pole Basin

Accurate estimates of geothermal heat flow (GHF) are critical for predicting basal melting and identifying stable sites for ancient ice, yet GHF remains one of the least constrained boundary conditions for the Antarctic Ice Sheet. We evaluate nine published Antarctic GHF models against radar‐derived specularity content in the South Pole Basin (SPB), a geologically complex region in central East Antarctica. We also simulate an ensemble of synthetic GHF fields via a three‐parameter Markov Chain Monte Carlo algorithm to constrain the spatial variability required to match observed bed conditions. No existing GHF map captures the observed gradient in basal conditions significantly better than a uniform GHF field. Instead, the radar observations require a spatial GHF gradient aligned with a major ice‐sheet and geomorphological boundary within the SPB. Constraining basal thermal state in this region will require methods sensitive to shallow crustal heterogeneity and integration of radar‐based indicators directly into model frameworks.