Dominant Factor in the Relationship Between Ice Thickness and Flow Velocity in the Downstream Region of Shirase Glacier, East Antarctica, Derived from Remotely Sensed Data

The buttressing effect of landfast sea ice is crucial for the stability of Antarctic outlet glaciers. This study investigated spatiotemporal variations in flow velocity and ice thickness at the Shirase Glacier, East Antarctica, from 2016 to 2025 using ALOS-2/PALSAR-2 and CryoSat-2/SIRAL data. Flow velocity increased, and ice thickness decreased downstream, exhibiting a significant negative correlation (r = −0.66, p < 0.05). Notably, during periods of unstable landfast ice (2017–2018 and 2023–2025), substantial ice flow acceleration occurred in the downstream ice tongue. Furthermore, basal melt rates calculated using the Eulerian flux divergence method revealed high melting (16–20 m a−1) near the grounding line, decreasing to 2–4 m a−1 mid-stream, and increasing to 4–8 m a−1 near the ice front. This distribution is consistent with the subglacial oceanic vertical thermal structure. These results quantitatively demonstrate the significant control of both landfast ice stability and subglacial ocean circulation on the spatiotemporal dynamics of the Shirase Glacier.