Ice shelf retreat decouples Piglet Glacier from the Pine Island catchment and amplifies dynamic mass loss

<title>Abstract</title> <p> Piglet Glacier, formed by ~ 20% area loss of the Pine Island Ice Shelf (2017–2020), is a compact analogue of a larger West Antarctic glacial drainage basin where ice shelf damage and retreat alter inland ice dynamics. Using Sentinel-1 feature-tracking ice velocities (Oct 2014-) and CryoSat-2 swath altimetry (Jul 2010-), we track change through May 2025. Relative to 2015–2017 mean, grounding-line ice speed rose by ~ 40%, and acceleration propagated ~ 50 km inland, with the upstream response lagging the grounding-line site by only ~ 1 month, indicating efficient transmission of reduced buttressing into grounded ice. Firn-corrected altimetry shows intensified dynamic thinning, with basin-integrated volume loss rising from ~ 2.9 to ~ 4.5 km ³ yr ^-1 (~ 60%). Downstream, post-calving acceleration focused along pre-damaged shear margins, and mélange loss in 2024–2025 coincided with further mechanical decoupling. Sustained shear-margin attrition and frontal retreat appear to be contributing to continued mass loss from Piglet Glacier and progressive fragmentation of the wider Pine Island system. These observations provide a rare benchmark showing how ice shelf retreat can propagate inland glacier and enhance dynamic mass loss, and indicate that models must include shear-margin damage, tributary detachment, and rapid stress transmission to improve near-term sea-level projections. </p>