Ruzica Dadic

Antarctic sea ice extent has shown increased variability since 2014. Although this variability has been attributed to a combination of oceanic and atmospheric forcings, considerable uncertainties remain. In coastal Antarctica, an important source of sea ice variability is the formation of polynyas and outbreaks of landfast sea ice, which are both influenced by complex atmospheric processes. While these processes can strongly impact regional sea ice variability, the links between large-scale atmospheric dynamics and regional sea ice extent remain incompletely understood. To address this gap, we investigate the sea ice extent in the McMurdo Sound during 2013–2024 using sea ice concentration data from the Japanese JAXA's GCOM-W1 satellite. More specifically, the study first introduces a pragmatic approach to identify polynya opening and fast ice breakout events from the satellite data (the sum of them referred to as “breakout events”) and then investigates local atmospheric flow anomalies and large-scale dynamical processes that influenced the interannual variability of breakout events. The results show that (i) the total number of breakout events varies between 3 and 8 per winter period (April to August), with mainly polynya openings until 2018 and mainly fast ice breakout events in the later years; (ii) in agreement with previous studies, breakout events are associated with strong southerly winds (typically >10 ms^-1) (iii) breakout events are further associated with warm anomalies of about 8 K at Marble Point; (iv) breakout events are related to the formation of the Ross Ice Shelf airstream, which is a barrier wind regime extending over more than 500 km along the Transantarctic Mountains; (v) breakout events (and the Ross Ice Shelf airstream) occur in response to enhanced large-scale sea level pressure gradients induced by (intense) cyclones in the Ross Sea; and (vi) the winter-mean frequency of Ross Sea cyclones correlates highly with the number of breakout events per winter. Together, our results reveal how large-scale atmospheric dynamics, particularly the frequency and intensity of Ross Sea cyclones, drive the formation and frequency of sea ice outbreak events and thus interannual sea ice variability in McMurdo Sound.

Summer Arctic sea ice forms a heterogeneous mosaic of melting ice, melt ponds, leads, and pressure ridges whose thermodynamic and aerodynamic contrasts can modify surface–atmosphere exchange. Direct observations quantifying these effects during the melt season remain scarce, limiting evaluation of how sea-ice heterogeneity should be represented in larger-scale models. During the CONTRASTS expedition in summer 2025, we performed eddy-covariance measurements at approximately 1m and 2m height on two mobile towers, complemented by spatially resolved near-surface air-temperature measurements, to compare atmospheric turbulent exchange across leads, melt ponds, pressure ridges, and the adjacent sea ice. Median sensible and latent heat fluxes were close to zero W m-2, although individual periods reached several tens of W m-2 in both directions. The near-surface atmospheric stability was mainly neutral, with modifications towards slightly stable (unstable) related to a warmer (colder) background air-mass temperature. Total turbulent flux variability reached about one third of the variability of simultaneously measured net radiation fluxes. At lead-ice transitions, a larger lead contribution to the flux footprint was associated with more negative sensible heat fluxes, because the saline lead water remained about 1.7°C colder than surrounding melting ice. In contrast, no systematic pond--ice flux difference was detected, consistent with both surfaces remaining near 0°C and without a detectable difference in moisture availability. Pressure-ridge wakes disrupted the vertical coherence of heat and momentum fluxes, with the strongest disturbances for near-perpendicular flow across the ridge. Because the mean turbulent heat exchange between the surface and the air was close to zero, even modest surface-induced perturbations could reverse its sign and thereby alter the turbulent contribution to the surface energy balance. Under the sampled summer conditions, aerodynamic perturbations associated with pressure ridges produced stronger local modifications of turbulent exchange than the comparatively weak thermodynamic differences between the sampled surface types. The thermodynamic influence of leads, however, depends critically on water temperature: the near-freezing saline leads observed during CONTRASTS acted as a local heat sink, whereas warmer leads as observed in other campaigns reverse the surface–air temperature difference and therefore the direction of turbulent heat exchange. These observations show that summer sea-ice heterogeneity cannot be characterized by surface morphology alone: the atmospheric response depends on the actual thermodynamic difference and dynamically induced flow distortion, and that footprint-resolved measurements are essential for quantifying and parameterizing turbulent exchange over heterogeneous sea ice.

Antarctic sea ice extent has shown increased variability since 2014. Although this variability has been attributed to a combination of oceanic and atmospheric forcings, considerable uncertainties remain. In coastal Antarctica, an important source of sea ice variability is the formation of polynyas and outbreaks of landfast sea ice, which are both influenced by complex atmospheric processes. While these processes can strongly impact regional sea ice variability, the links between large-scale atmospheric dynamics and regional sea ice extent remain incompletely understood. To address this gap, we investigate the sea ice extent in the McMurdo Sound during 2013–2024 using sea ice concentration data from the Japanese JAXA's GCOM-W1 satellite. More specifically, the study first introduces a pragmatic approach to identify polynya opening and fast ice breakout events from the satellite data (the sum of them referred to as “breakout events”) and then investigates local atmospheric flow anomalies and large-scale dynamical processes that influenced the interannual variability of breakout events. The results show that (i) the total number of breakout events varies between 3 and 8 per winter period (April to August), with mainly polynya openings until 2018 and mainly fast ice breakout events in the later years; (ii) in agreement with previous studies, breakout events are associated with strong southerly winds (typically >10 ms-1) (iii) breakout events are further associated with warm anomalies of about 8 K at Marble Point; (iv) breakout events are related to the formation of the Ross Ice Shelf airstream, which is a barrier wind regime extending over more than 500 km along the Transantarctic Mountains; (v) breakout events (and the Ross Ice Shelf airstream) occur in response to enhanced large-scale sea level pressure gradients induced by (intense) cyclones in the Ross Sea; and (vi) the winter-mean frequency of Ross Sea cyclones correlates highly with the number of breakout events per winter. Together, our results reveal how large-scale atmospheric dynamics, particularly the frequency and intensity of Ross Sea cyclones, drive the formation and frequency of sea ice outbreak events and thus interannual sea ice variability in McMurdo Sound.

Surface roughness is a key control on turbulent exchange over glaciers, yet it is still commonly treated as a constant or tuning parameter in surface energy balance models. This simplification stands in contrast to the strong spatial heterogeneity and temporal evolution of glacier surfaces, particularly during the ablation season. A better understanding of how roughness varies, and how this variability translates into aerodynamic properties, is therefore essential for improving representations of surface–atmosphere exchange in mountainous terrain.Here, we investigate glacier surface roughness using a combination of turbulence measurements from eddy covariance systems and high-resolution digital elevation models (DEMs) derived from close-range photogrammetry, acquired during recent field campaigns on Silvrettagletscher and Hintereisferner. Turbulence data are filtered to retain periods that approximately satisfy the assumptions required for applying the bulk aerodynamic method, allowing for consistent estimates of aerodynamic roughness length. In parallel, roughness length is derived from the DEMs using a microtopographic approach based on the Lettau formulation, explicitly accounting for the orientation of surface elements relative to the flow.Both turbulence-based estimates and microtopographic analysis consistently show that roughness length depends on wind direction. In particular, lower roughness lengths are found for along-glacier (katabatic) flow compared to cross-glacier flow. This behaviour is present on both glaciers, reflecting the anisotropic structure of the glacier surface with roughness elements that tend to be aligned with the flow direction at larger scales. As a result, the effective aerodynamic roughness experienced by the flow varies with wind direction relative to the glacier flowline, and cannot be represented by a single, direction-independent parameter. In addition, a clear temporal evolution is observed over the ablation season: Roughness sharply decreases during the transition from snow-covered to ice surfaces, followed by a progressive increase as melt features such as channels and cavities develop and organize the surface.These results show that glacier surface roughness is highly variable in space, time, and direction. This variability has direct implications for the parametrization of turbulent fluxes and suggests that commonly used approaches based on a single roughness length may be insufficient to capture the complexity of glacier–atmosphere interactions.

Snow on sea ice exerts strong controls on Antarctic sea ice thermodynamics and mass balance by modulating both radiative and conductive transfers in the surface energy budget. The high albedo of snow reduces absorbed shortwave radiation, while its relatively low but variable thermal conductivity insulates the ice, altering internal ice temperature gradients, growth rates and thus the timing and magnitude of basal heat flux to the ocean. Snow properties exhibit large spatial and temporal variability and assuming fixed snow-thermal parameters in models can bias conductive fluxes and the surface energy balance. For Antarctica in particular, thicker, storm-fed snowpacks modify vertical heat transfer. In this study we examine the influence of snow on Antarctic sea ice through the thermodynamics observed by three SIMBA bouys, which measure temperature at high spatial and temporal resolution through the snow and sea ice column. The three buoys were placed in locations with varying snow thickness (14cm, 2cm, 0cm). Using measurements of snow physical properties (thermal conductivity, surface temperature and roughness, snow grain radius, and albedo) to constrain the column physics model ICEPACK we examine the thermodynamics of the three sites. The results clearly indicate the influence of even very thin snow cover on sea ice, which makes internal sea ice temperatures much colder. The SIMBA bouy at the deeper snow site was maintained over two melt seasons and winter, and using this long time series shows that the model is most sensitive to variations in the key parameters of thermal conductivity and snow grain radius. These findings provide observationally grounded constraints on snow/ice thermodynamics that can improve sea ice models used in climate projections.

Antarctica InSync is a global effort to synchronise research across Antarctica and the Southern Ocean, connecting ice, ocean, land, climate, and life to protect this vital region. This roadmap paper introduces the scientific and technological motivation and action plan to build an international programme for a coordinated field season in Antarctica and its surrounding seas. It lays out the international collaboration that is required to realise an ambitious action plan and the opportunities for the science community to address important scientific themes that identify current knowledge gaps. In the spirit of the Antarctic Treaty Consultative Meeting (ATCM), the planned scientific action mandates free data exchange, facilitates international collaboration, and derives expert scientific advice together with the Scientific Committee on Antarctic Research (SCAR). Aligned with challenges of the United Nation Ocean and Cryosphere Decades, we plan a shared global effort to better understand the role of Antarctica and its surrounding ocean for our global futures, building on decades of achievements in polar and ocean science. As a milestone leading up to the next International Polar Year in 2032/33 (IPY5), the ambition is to achieve a new level of cooperation, with opportunities for the next generation of polar scientists around the world by enhancing practices in sharing of ideas, infrastructure and information.

Since 2015, Antarctic sea ice has entered a period of persistent record-low extent after decades of strong regional variability and large swings. The speed and persistence of this decline point to a system that may be changing state, with implications for the Southern Ocean, Antarctic ecosystems, and the global climate system. What is driving this shift remains insufficiently understood. Atmospheric variability plays a role, but ocean processes, including subsurface heat release and changes in stratification, are increasingly recognized as key pieces of the puzzle, alongside feedbacks involving snow, ice shelves, clouds, and freshwater input. This white paper focuses on four areas where progress is needed. First, improved understanding is needed of sea ice mass balance and dynamics: how sea ice grows, melts, moves, and deforms. Second, exchanges of heat, mass, and momentum between ocean, atmosphere, sea ice, and ice shelves need to be quantified across seasons and regions. Third, the consequences for ecosystems and biogeochemistry are likely substantial. Sea ice supports productive microbial communities and carbon and nutrient cycling, so its decline will affect polar food webs and Southern Ocean carbon storage. Finally, climate feedbacks, from albedo changes to cloud and ocean interactions, remain poorly constrained but could amplify ongoing change. A recurring limitation is the lack of coordinated, year-round observations across Antarctica. Existing data are sparse and uneven in space and time. Antarctica InSync is designed to address this by bringing together satellite observations, autonomous platforms, field campaigns, coastal observatories, harmonized data products, and modelling across pack ice, the marginal ice zone, landfast ice, and polynyas. The white paper recommends standardized observations of essential sea ice, snow, ocean, atmospheric, ecosystem, and biogeochemical variables, integrated into interoperable data products and models. Addressing these gaps is essential to improve predictability and anticipate future Antarctic sea ice change.