Abstract
Basal melting of ice shelves is fundamental to Antarctic Ice Sheet mass
loss, yet direct observations are sparse. We present the first melt
record (2017 to 2021) from a phase-sensitive radar at Fimbulisen, East
Antarctica, one of the fastest flowing ice shelves in Dronning Maud
Land. The observed long-term mean ablation below the central part of the
ice shelf was 1.0 ±0.4 m yr–1, marked by substantial sub-weekly
variability ranging from 0.3 to 3.8 m yr–1. 36-h filtered fluctuations
in basal melt exhibit a close alignment with ocean velocity, revealing
shear-driven turbulent heat transfer as the predominant driver of melt
variability at sub-weekly to monthly timescale. Seasonally, basal melt
rates are highest in the austral summer, when ocean temperature is
higher. Our observed in-situ melt rates show threefold lower amplitudes
and a 3-month delay in seasonality compared to satellite-derived melt
rates, however, the long-term multi-year mean is of similar magnitude
(1.0 m yr–1 vs 0.8 m yr–1). Our detailed ice–ocean observations
provide essential validation data for remote sensing and numerical
models aiming to measure and project ice-shelf response to ocean
forcing. In-situ measurements and continued monitoring are crucial for
accurately assessing and modelling future basal melt rates, as well as
understanding the complex dynamics driving ice-shelf stability and
sea-level change.