Subglacial Topography of Coats Land Records Post‐Gondwanan Landscape Evolution and Early Ice‐Sheet Behavior in East Antarctica

Abstract The East Antarctic Ice Sheet (EAIS) formed circa 34 million years ago and now contains an ice volume equivalent to ∼52 m of global sea‐level rise. Although the EAIS is approximately in balance today, there is substantial uncertainty regarding the sensitivity of sectors underlain by low‐lying bed topography to future climate and ocean warming. This is especially pertinent for Coats Land (eastern Weddell Sea), where geological records of past ice‐sheet changes are sparse. Here, we use airborne radio‐echo sounding and magnetic data, satellite imagery, and isostatic modeling to map the subglacial geomorphology of Coats Land for the first time and constrain the regional geological and ice‐sheet history. Our mapping reveals topographic features such as tilted highlands and deep, asymmetric depressions, which likely formed via regional extension associated with Gondwana breakup, concomitant with early Jurassic magmatism. We also document low‐relief, seaward‐dipping surfaces that we infer to be remnants of coastal plains formed by fluvial erosion after continental breakup. Subglacial troughs that were incised into (i.e., post‐date) these pre‐glacial erosion surfaces were selectively eroded by ice flowing south‐to‐north. The ice within these troughs is stagnant today, indicating that they did not form beneath the modern (east‐to‐west‐flowing) EAIS. Based on local geomorphological and geochronological evidence, we infer that these troughs were most likely incised during an interval of the Oligocene–Miocene (ca. 34–14 Ma) when the regional ice configuration and bed topography were significantly different from today. Subsequent EAIS reconfiguration switched off these early outlets and facilitated widespread landscape preservation beneath regionally non‐erosive ice.