Prior to the present study, no dedicated in situ measurement of the thickness distributions of fast ice and the sub-ice platelet layer, formed by supercooled Ice Shelf Water in the near-surface ocean, had been carried out in Terra Nova Bay. Previous studies have recognised the biological importance of the sub-ice platelet layer observed beneath fast ice beside the Campbell Ice Tongue. Furthermore, a recent airborne survey of fast ice in the western Ross Sea implied that smaller ice bodies (ice tongues and outlet glaciers) contribute to the formation of supercooled Ice Shelf Water. With the objective of inferring source regions and circulation of Ice Shelf Water, we measured fast ice and sub-ice platelet layer thickness distributions near the Campbell Ice Tongue in late spring of 2021, using drill hole surveys and high-resolution ground-based electromagnetic induction soundings. We observed thicker fast ice and sub-ice platelet layer near the ice tongue with very thick and narrow sub-ice platelet layer maxima identifying highly channelled outflow of supercooled Ice Shelf Water from beneath the ice tongue through ice mélange, subglacial formations, and grounded regions. We conclude that a significant volume of supercooled Ice Shelf Water is locally sourced from the Campbell Ice Tongue through basal melting and affirm that the icescape in north Terra Nova Bay results from a complex interplay of glacial morphology, bathymetry, polynya dynamics, and ocean circulation.

The genesis of snowdrifts and its governing processes are not fully understood. Yet, the assessment of snow redistribution by the wind is essential in snow-affected regions for risk management, water resources and mitigation tactics. Factors such as flow turbulence and snow properties showed to be crucial for the snow-wind interaction on flat terrain. In this work, we add a third component and investigate the drifting mechanisms of snow around complex building structures using numerical Euler-Lagrange simulations. The German Antarctic research station Neumayer III is investigated in particular. Results show that structure-borne snowdrifts are strongly influenced by the wind forcing, precipitation, snow cohesion and fine changes in the obstacle shape. Thus, these factors should be cautiously included in numerical models simulating snow transport at small scales.

We present a 700 km airborne electromagnetic survey of late-spring fast ice and sub-ice platelet layer (SIPL) thickness distributions, from McMurdo Sound to Cape Adare, providing a first-time inventory of thickness close to its annual maximum. The overall modal consolidated ice (including snow) thickness was 1.9 m, less than its mean of 2.6±1.0 m. Our survey was partitioned into level and rough ice, and SIPL thickness was estimated under level ice. Although results show a prevalence of level ice, with a mode of 2.0 m and mean of 2.0±0.6 m, rough ice covered 41% of the transect by length, 50% by volume, with a mode of 3.3 m and mean of 3.2±1.2 m. The thickest 10% of rough ice was almost 6 m on average, and a 2 km segment in Moubray Bay had a thickness greater than 8 m, demonstrating the overwhelming influence of deformation against coastal features. The fast ice was thus significantly thicker than adjacent pack ice. The presence of a significant SIPL was observed in Silverfish Bay, offshore Hells Gate Ice Shelf, New Harbour, and Granite Harbour where the SIPL transect volume was a significant fraction (0.30) of the consolidated ice volume. The thickest 10% of SIPLs had an average thickness of nearly 3 m, and near Hells Gate Ice Shelf the SIPL was almost 10 m thick, implying vigorous heat loss to the ocean (~ 90Wm-2). We conclude that polynya-induced deformation and interaction with continental ice influence fast ice thickness in the western Ross Sea.

Melt ponds have a strong impact on the Arctic surface energy balance and the ice-associated ecosystem because they transmit more solar radiation compared to bare ice. In the existing literature, melt ponds are considered as bright windows to the ocean, even during freeze-up in autumn. In the central Arctic during the summer-autumn transition in 2018, we encountered a situation where more snow accumulated on refrozen melt ponds compared to the adjacent bare ice, leading to a reduction in light transmittance of the ponds even below that of bare ice. Supporting results from a radiative transfer model suggest that melt ponds with a snow cover >0.04 m lead to lower light transmittance than adjacent bare ice. This scenario has not been described in the literature before, but has potentially strong implications for example on autumn ecosystem activity, oceanic heat budget and thermodynamic ice growth.

The formation of platelet ice is well known to occur under Antarctic sea ice, where sub-ice platelet layers form from supercooled ice shelf water. In the Arctic however, platelet ice formation has not been extensively observed and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long-term in situ observations of a decimeter thick sub-ice platelet layer under free-drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition, provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth.