Seven-Year Sentinel-1 C-Band SAR Time Series Reveals Brine Infiltration Signatures and Progressive Firn Densification Across Antarctic Ice Shelves

Antarctic ice shelf stability is sensitive to seawater infiltration in the firn layer, yet satellite confirmation of brine signatures remains limited at C-band frequencies. Cook et al. (2018) identified five ice shelves as the highest-priority candidates for brine infiltration. We present a seven-year (2019–2025) Sentinel-1 C-band SAR backscatter time series for all five sites in Extra Wide swath HH+HV mode, providing the first systematic C-band characterisation of seasonal backscatter contrasts and interannual trends across these sites. Gamma0 statistics were extracted from 180 scene-site observations using site-specific geographic bounding boxes across six sampled months per year. Nickerson Ice Shelf exhibits anomalously low winter HH backscatter (−14.69 dB), near-zero seasonal contrast (+0.54 dB), and suppressed HH/HV ratio (5.73 dB; p < 0.001), consistent with year-round brine infiltration. Sulzberger shows a non-significant seasonal contrast (+0.24 dB; p = 0.112) and suppressed HH/HV ratio (6.84 dB; p < 0.001), consistent with moderate brine suppression of firn backscatter variability. Shackleton and Abbot exhibit positive seasonal contrasts (+2.73 and +1.46 dB), consistent with the absence of persistent brine, though East Antarctic site statistics may include seasonal sea ice contributions. All four main sites show significant negative trends in winter HH backscatter over 2019–2025 (−0.138 to −0.281 dB yr⁻¹; p ≤ 0.003), substantially exceeding the Sentinel-1A radiometric stability threshold, indicating progressive changes in firn or surface properties. These findings provide the first C-band satellite evidence for brine-related backscatter anomalies at Nickerson and Sulzberger and reveal systematic backscatter decline across multiple Antarctic ice shelves.

Data and code

All data and analysis scripts are openly available on Zenodo: https://doi.org/10.5281/zenodo.20408208

Submitted to IJRS, special issue “Cryospheric Hazards in a Warming World”; currently in editor review.

Author: Shobha Mourya Dumpati, FGS, FRGS