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.

The access of heat to the Antarctic ice shelf cavities is regulated by the Antarctic Slope Front, separating relatively warm offshore water masses from cold water masses on the continental slope and inside the cavity. Previous observational studies along the East Antarctic continental slope have identified the drivers and variability of the front and the associated current, but a complete description of their seasonal cycle is currently lacking. In this study, we utilize two years (2019-2020) of observations from two oceanographic moorings east of the prime meridian to further detail the slope front and current seasonality. In combination with climatological hydrography and satellite-derived surface velocity, we identify processes that explain the hydrographic variability observed at the moorings. These processes include (i) an offshore spreading of seasonally formed Antarctic Surface Water, resulting in a lag in salinity and thermocline depth seasonality toward deeper isobaths, and (ii) the crucial role of buoyancy fluxes from sea ice melt and formation for the baroclinic seasonal cycle. Finally, data from two sub-ice-shelf moorings below Fimbulisen show that flow at the main sill into the cavity seasonally coincides with a weaker slope current in spring/summer. The flow is directed out of the cavity in autumn/winter when the slope current is strongest. The refined description of the variability of the slope current and front contributes to a more complete understanding of processes important for ice-shelf-ocean interactions in East Antarctica.

We present year-round estimates of liquid freshwater transport (FWT) in the East Greenland Current (EGC) in the western Fram Strait from mooring observations since 2015. Novel data from additional instruments deployed in recent years are used to correct earlier estimates when instrument coverage was lower. The updated FWT time series (reference salinity 34.9) show that the increased export between 2010 and 2015 has not continued, and that FWT has decreased to pre-2009 levels. Salt transport independent of a reference salinity is shown not to be sensitive to salinity changes. Between 2015-2019, the FWT in the Polar Water decreased to an average of 56.9 (±4.5) mSV, 15% less than the 2003-2019 long-term mean, however, high FWT events occurred in 2017. The overall decrease is related with a slowdown of the EGC, partly attributed to a decrease of the baroclinic component, due to salinification of the halocline waters (26.5 < σθ < 27.7 kg/m3) which counterbalanced the freshening of the surface layer (σθ < 26.5 kg/m3). Our results show changes in the Polar Water between 2003-2019: Salinity stratification increased as the salinity difference between 155 and 55 m increased by 0.63 psu , the Polar Water layer became thinner by 46 m and the Polar-Atlantic front moved abruptly west in June 2015. All processes point to an “Atlantification” of the western Fram Strait and reduced Polar outflow. Including the novel data sets decreased the uncertainty of the FWT to an average of 8% after 2015, as opposed to 17% in earlier estimates.