Building multi-satellite DEM time series for insight into mélange inside large rifts in Antarctica

Abstract. Front calving is a primary mechanism through which Antarctic ice shelves discharge ice mass into the Southern Ocean. It is an important process that influences ice shelf stability and thus, impacts the Antarctic Ice sheet's contribution to global sea level rise. Mélange dynamics inside rifts is recognized to potentially influence the rift propagation and subsequent iceberg calving. However, large-scale, high-resolution three-dimensional (3D) observations are scarce, which leads to their inability to capture small scale rift dynamics. Ultimately, the lack of knowledge in 3D rift structural changes and mélange dynamics hinders our understanding of the role of mélange in ice shelf retreat and mechanisms underlying the weakening of ice shelf stability. We propose an innovative multi-temporal digital elevation model (DEM) adjustment model (MDAM) to build a multi-satellite DEM time series from meter-level resolution small DEMs. It removes biases across large Antarctic ice shelves, as large as ∼ 6 m in elevation, caused by tides, ice flow dynamics, and observation errors. Using 30 Reference Elevation Model of Antarctica (REMA) and ZY-3 sub-DEMs, we establish a cross-shelf DEM time series from 2014 to 2021 for the Filchner-Ronne Ice Shelf, the second largest ice shelf in Antarctica. This unified and integrated DEM series, with an unprecedented submeter elevation accuracy, reveals quantitative 3D structural and mélange features of two ∼ 50 km long rifts, including rift lips, flank surface, pre-mélange cavities, and mélange elevations. For the first time, we have observed that while the mélange elevation in the rifts decreased by 2.7 ± 0.6 m from 2014 to 2021, the mélange within the rifts experienced a rapid expansion of (10.31 ± 0.03) × 109 m3, or 139 %. This expansion is attributed to newly calved shelf ice from rift walls, associated rift widening, and other factors related to rift-mélange interactions. The developed MDAM system and the 3D mélange dynamics analysis methods can be applied for quantifying ice shelf instability and the future contribution of the Antarctic Ice Sheet to global sea level rise.