This study investigates how the marine sediment proxies signal reflects dissolved oxygen levels in fjord basin water, to improve our understanding of the coastal marine deoxygenation that has been associated with the ongoing climate change. We use western Norwegian fjords to test how marine sediment proxies for dissolved oxygen perform. Such knowledge is needed to evaluate if recent reduced renewal of fjord basin waters is driven by anthropogenic impact or is within the range of natural variability. We have explored the potential and limitations of Mn/Ca, δ¹³C, benthic foraminiferal diversity, the calcareous and agglutinated foraminifera ratio, and the benthic foraminifera indicator species Stainforthia fusiformis, as potential proxies for bottom water oxygen concentrations. Among the fjords investigated in western Norway, seven stations are well-oxygenated, one is close to hypoxic oxygen levels, and one shows nearly anoxic conditions. The relative abundance of S. fusiformis shows the strongest potential as a tool for reconstructing past oxygen concentrations. The Mn/Ca and δ¹³C measured in the seawater also strongly correlate with dissolved oxygen. The foraminiferal diversity indices follow the oxygenation gradient in the fjords. The calcareous/agglutinated species ratio has limitations under anoxic conditions, where almost monospecific assemblage dominated by calcareous S. fusiformis was found. The signal of Mn/Ca and δ¹³C measured in shells of species Hyalinea balthica was difficult to assess due to low species abundance at some fjord sites. Hence, further analyses are necessary to employ the Mn/Ca and δ¹³C in foraminiferal shells as proxies for reconstructing past oxygen concentrations in fjords.

The Antarctic Slope Front and the associated Antarctic Slope Current are central in determining the dynamics along and the exchanges across the continental shelf break around Antarctica. Here, we present new, four-year-long (2017-2021) records from two moorings deployed on the upper part of the continental slope (530 m and 738 m depth) just upstream of the Filchner Trough in the southern Weddell Sea. We use the records to describe the mean state and the seasonal variability of the shelf break current and the regional hydrography. We find that (i) the current is bottom enhanced, (ii) the isotherms slope upwards towards the shelfbreak, and more so for warmer isotherms, and (iii) the monthly mean thermocline depth is shallowest in February-March and deepest in May-June while (iv) the current is strongest in April-June. On monthly timescales, we show that (v) positive (warm) temperature anomalies of the de-seasoned records are associated with weaker-than-usual currents. Our results contribute to the understanding of how warm ocean waters propagate southward and potentially affect basal melt rates at the Filchner-Ronne Ice Shelf.

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.