Contrasting Terminus Dynamics of Lake-Terminating Glaciers in Lago Argentino (Patagonia), 2016–2026: A Training-Free Sentinel-2/Sentinel-1 Workflow

Lake-terminating glaciers of the Southern Patagonian Icefield are retreating rapidly, yet dense multi-glacier records of their termini remain scarce. We present a training-free workflow in Google Earth Engine that measures ice-area change within a fixed terminus domain from every usable Sentinel-2 scene (per-scene Otsu threshold on the near-infrared band, with cloud screening restricted to lake pixels) and delineates annual terminus positions automatically. Applied to Perito Moreno, Upsala and Spegazzini glaciers (Lago Argentino, Argentina) for October–March 2016–2026, it yielded 260 scenes. Perito Moreno showed no significant trend until mid-2019 and then lost 0.39 km2 a−1 (p < 0.001); its terminus retreated by about 580 m in nine summers; the two most recent summers showed the largest seasonal losses of the record (≈1.6–1.7 km2); and in March 2026 the front detached from Península de Magallanes. Upsala retreated by about 1010 m (≈130 m a−1), whereas Spegazzini remained within ±100 m of its 2017 position. Warm, dry summers in 2021–2022 affected all three glaciers, so their contrasting responses suggest that basin geometry and lateral support modulate the response to a common climate. Sentinel-1 reproduced the Perito Moreno decline but failed in iceberg-choked Brazo Upsala.