Alexander D. Fraser

Coastal polynyas are recurring regions of open water within sea ice that serve as sea-ice factories, producing vast amounts of new ice relative to nearby sea-ice-covered regions. Their formation and persistence are commonly attributed to strong offshore winds, while the influence of waves on polynya dynamics remains largely unexplored. Using rare wave-buoy observations from the Vincennes Bay Polynya, we show that strong winds generate energetic waves capable of breaking surrounding sea ice from the inside-outward, contrasting with outside-inward breakup caused by Southern Ocean swells. Satellite records from 2003–2022 reveal that extreme wave-induced breakup events coincide with substantial reductions in sea-ice concentration that persist for at least one week, accompanied by increased transitions to active frazil ice. These findings demonstrate that locally generated waves impact polynya dynamics and reshape surrounding sea-ice conditions. As Antarctic coastal polynyas evolve under a changing climate, wave activity may become increasingly important in shaping their sea-ice conditions and evolution.

Icebergs frequently run aground on shoals on the continental shelf around Antarctica. Once rendered immobile, they can anchor landfast sea ice (fast ice) and their supply of limiting trace nutrients contribute to driving coastal marine productivity. They are also associated with seabed scouring, with implications for benthic marine ecosystems. Despite their importance, there is currently a lack of accurate, continent-wide automated mapping of grounded iceberg distribution and size and as a consequence, no large-scale, complete map of grounded icebergs exists. To address these gaps, this study implements an automated grounded iceberg detection framework based on Sentinel-1 Synthetic Aperture Radar (SAR) imagery, integrating a proposed ResUNet deep-learning network with a multi-temporal identification algorithm, incorporating strict physical constraints derived from bathymetry and sea ice concentration to mitigate environmental false positives. The method demonstrates strong robustness against interference from complex coastal conditions, achieving a detection F1 score exceeding 0.91 and successfully reducing the minimum detectable iceberg size to 0.016 km ² . Since the presence of fast ice makes distinction between “truly grounded icebergs” and “those held motionless by fast ice”, we capitalise on the unprecedented low fast ice extent in early 2025 (late February to early April) to construct the first high-resolution, continent-wide dataset of grounded icebergs around Antarctica. A total of 39 619 stationary icebergs were identified on the Antarctic continental shelf. We partition these stationary targets into “high-confidence grounded icebergs” and fast ice-entrapped candidates. Analysis shows that 67.4 % of these targets are identified as high-confidence grounded. Across the entire dataset, tiny icebergs (2 ) dominate numerically, accounting for 92.6 % of the total. These high-density grounded iceberg clusters are primarily concentrated on shallow continental shelves and west of (i.e., downstream of) the actively disintegrating fronts of ice shelves, forming complex and discontinuous “grounded iceberg chains”. Our dataset reveals that these grounded icebergs cover a combined area of 13 430 km ² and are widely distributed along 56.5 % of the Antarctic coastline, with just 14.2 % of the coastline containing 80 % of all grounded icebergs. Crucially, while typically overlooked, tiny icebergs (2 ) contribute 53.9 % of this total grounded area. These dense clusters imply a potential “picket fence effect”, acting as a series of physical anchors to stabilise fast ice. This provides a quantitative baseline for modelling fast ice stability, assessing nutrient fluxes, and mapping benthic habitats. The grounded iceberg dataset (Jiao et al., 2026) is available at https://doi.org/10.25959/54sx-pt47.

Snow on Antarctic sea ice modulates albedo, thermodynamic growth, and snow–ice formation, yet remains a leading uncertainty in altimetry‐derived sea‐ice thickness. Here we use the post‐2022 CRYO2ICE configuration to derive along‐track winter snow thickness from ICESat‐2 laser and CryoSat‐2 Ku‐band radar freeboards over the Weddell and Ross sectors. We analyze 82,341 winter matchups (August 2022–September 2025) using a 5 km, 4 hr collocation criterion and propagate freeboard and snow‐density uncertainties. Retrieved snow thickness is consistently larger in the Weddell Sea (mean 0.255 m, median 0.188 m) than the Ross Sea (0.217 m, 0.156 m), consistent with the older, thicker western Weddell ice. The contrast persists across sampled months and years and under common snow‐density and penetration‐factor assumptions. Formal per‐matchup precision (0.039–0.040 m) is dominated by CryoSat‐2 radar‐freeboard uncertainty, whereas the absolute magnitude is set by the unresolved Ku‐band scattering horizon. Comparison with AMSR2 passive‐microwave snow depth shows weak point‐to‐point agreement ( and in the Weddell and Ross sectors), reflecting differing measurement physics and spatial support. Nevertheless, both independently reproduce thicker Weddell than Ross snow. Under a common penetration factor, absolute sector‐mean snow thickness varies by approximately a factor of two across the tested range, whereas the sector ordering is preserved under any uniform choice of penetration factor. CRYO2ICE therefore resolves a repeatable regional freeboard‐difference signal, but conversion of that signal to absolute snow thickness remains conditional on the poorly constrained, ice‐regime‐dependent Ku‐band scattering horizon.

Landfast sea ice (fast ice) is a prominent feature of the Antarctic coastal environment. It plays key roles as a climate driver in the hydrological dynamics of the Antarctic continental shelf and serves as a critical habitat. However, despite its importance, Antarctic fast ice remains poorly represented in most global climate models. This study addresses key knowledge gaps in sea-ice modelling for realistically simulating Antarctic fast ice within an elastic-viscous-plastic rheological framework using a stand-alone sea-ice model. We conduct a suite of pan-Antarctic 1/4° stand-alone sea-ice model simulations to quantify the role of grounded icebergs and to systematically test the influence of key rheological parameters (yield-curve ellipse aspect ratio, tensile strength, and ice strength) in sustaining fast ice. To support this, we introduce a new grounded iceberg dataset and a method to prescribe realistic grounded iceberg distributions based on observations. Our results show that the model reproduces the observed spatial distribution, seasonal maximum, and growth and retreat rates of Antarctic fast ice. Simulated fast ice reproduces the observed seasonal climatology but captures only limited inter-annual variability in circum-Antarctic fast-ice area. We demonstrate that simulated fast ice is highly sensitive to the ellipse aspect ratio (controlling the shear strength of the yield curve), tensile strength magnitude, and the presence and distribution of grounded icebergs. Realistic Antarctic fast ice is produced with an ellipse aspect ratio of 1.2, a tensile strength of 0.2, and a prescribed pan-Antarctic grounded iceberg extent of ~580 grid cells distributed consistently with observations. In this configuration, comparison with an otherwise similar simulation without grounded icebergs indicates that approximately 83 % of simulated fast-ice area depends on grounded icebergs as mechanical anchoring points. Importantly, these rheology and grounded iceberg modifications do not degrade the simulation of overall sea-ice area, thickness, or velocity in the Southern Ocean in our stand-alone simulations. These findings provide practical guidance for improving Antarctic fast-ice representation in coupled climate models through realistic grounded iceberg representation and targeted tuning of rheological parameters.

Landfast sea ice (fast ice) is a prominent feature of the Antarctic coastal environment. It plays key roles as a climate driver in the hydrological dynamics of the Antarctic continental shelf and serves as a critical habitat. However, despite its importance, Antarctic fast ice remains poorly represented in most global climate models. This study addresses key knowledge gaps in sea-ice modelling for realistically simulating Antarctic fast ice within an elastic-viscous-plastic rheological framework using a stand-alone sea-ice model. We conduct a suite of pan-Antarctic 1/4° stand-alone sea-ice model simulations to quantify the role of grounded icebergs and to systematically test the influence of key rheological parameters (yield-curve ellipse aspect ratio, tensile strength, and ice strength) in sustaining fast ice. To support this, we introduce a new grounded iceberg dataset and a method to prescribe realistic grounded iceberg distributions based on observations. Our results show that the model reproduces the observed spatial distribution, seasonal maximum, and growth and retreat rates of Antarctic fast ice. Simulated fast ice reproduces the observed seasonal climatology but captures only limited inter-annual variability in circum-Antarctic fast-ice area. We demonstrate that simulated fast ice is highly sensitive to the ellipse aspect ratio (controlling the shear strength of the yield curve), tensile strength magnitude, and the presence and distribution of grounded icebergs. Realistic Antarctic fast ice is produced with an ellipse aspect ratio of 1.2, a tensile strength of 0.2, and a prescribed pan-Antarctic grounded iceberg extent of ~580 grid cells distributed consistently with observations. In this configuration, comparison with an otherwise similar simulation without grounded icebergs indicates that approximately 83 % of simulated fast-ice area depends on grounded icebergs as mechanical anchoring points. Importantly, these rheology and grounded iceberg modifications do not degrade the simulation of overall sea-ice area, thickness, or velocity in the Southern Ocean in our stand-alone simulations. These findings provide practical guidance for improving Antarctic fast-ice representation in coupled climate models through realistic grounded iceberg representation and targeted tuning of rheological parameters.

Estimates of Antarctic sea-ice thickness from satellite altimetry depend not only on measured freeboards but on prescribed snow depth, snow density, bulk sea-ice density, and the Ku-band scattering horizon.In the total-freeboard formulation, the penetration fraction enters thickness only through retrieved snow depth, so perturbing penetration while holding snow depth fixed suppresses its contribution by construction.We develop a coupled Monte Carlo framework in which snow depth is re-derived at every realisation from the laser-radar freeboard difference, and apply it to 65,165 positive-freeboard matchups from a winter CRYO2ICE dataset of 82,341 coincident ICESat-2 and CryoSat-2 observations over the Weddell and Ross seas (2022-2025).Within this error model, bulk sea-ice density and Ku-band penetration are co-dominant residual uncertainties, contributing 42% and 40% of the propagated per-matchup thickness variance; freeboards and snow density account for the remaining 18%.This ranking is specific to dual-altimetry retrieval, which relocates the leading single-band uncertainty, prescribed snow depth, into the penetration fraction.The two terms change order with ice type, penetration leading over multi-year ice (48%) and density over first year ice.A penetration-fraction uncertainty of 0.10 to 0.15 marks a crossover below which density dominates in every sector, a precision benchmark for dual- and triple-frequency missions, including CRISTAL.Substituting the CRYO2ICE snow retrieval for the passive-microwave climatology in two CryoSat-2 thickness products raises median hydrostatic thickness by 0.62 to 0.67 m, comparable to reported decadal changes.Constraining Antarctic sea-ice thickness from dual altimetry requires concurrent progress on snow, penetration, and density.

Landfast sea ice (fast ice) is a prominent feature of the Antarctic coastal environment. It plays key roles as a climate driver in the hydrological dynamics of the Antarctic continental shelf and serves as a critical habitat. However, despite its importance, Antarctic fast ice remains poorly represented in most global climate models. This study addresses key knowledge gaps in sea-ice modelling for realistically simulating Antarctic fast ice within an elastic-viscous-plastic rheological framework using a stand-alone sea-ice model. We conduct a suite of pan-Antarctic 1/4° stand-alone sea-ice model simulations to quantify the role of grounded icebergs and to systematically test the influence of key rheological parameters (yield-curve ellipse aspect ratio, tensile strength, and ice strength) in sustaining fast ice. To support this, we introduce a new grounded iceberg dataset and a method to prescribe realistic grounded iceberg distributions based on observations. Our results show that the model reproduces the observed spatial distribution, seasonal maximum, and growth and retreat rates of Antarctic fast ice. Simulated fast ice reproduces the observed seasonal climatology but captures only limited inter-annual variability in circum-Antarctic fast-ice area. We demonstrate that simulated fast ice is highly sensitive to the ellipse aspect ratio (controlling the shear strength of the yield curve), tensile strength magnitude, and the presence and distribution of grounded icebergs. Realistic Antarctic fast ice is produced with an ellipse aspect ratio of 1.2, a tensile strength of 0.2, and a prescribed pan-Antarctic grounded iceberg extent of ~580 grid cells distributed consistently with observations. In this configuration, comparison with an otherwise similar simulation without grounded icebergs indicates that approximately 83 % of simulated fast-ice area depends on grounded icebergs as mechanical anchoring points. Importantly, these rheology and grounded iceberg modifications do not degrade the simulation of overall sea-ice area, thickness, or velocity in the Southern Ocean in our stand-alone simulations. These findings provide practical guidance for improving Antarctic fast-ice representation in coupled climate models through realistic grounded iceberg representation and targeted tuning of rheological parameters.

Landfast sea ice (fast ice) is a prominent feature of the Antarctic coastal environment. It plays key roles as a climate driver in the hydrological dynamics of the Antarctic continental shelf and serves as a critical habitat. However, despite its importance, Antarctic fast ice remains poorly represented in most global climate models. This study addresses key knowledge gaps in sea-ice modelling for realistically simulating Antarctic fast ice within an elastic-viscous-plastic rheological framework using a stand-alone sea-ice model. We conduct a suite of pan-Antarctic 1/4° stand-alone sea-ice model simulations to quantify the role of grounded icebergs and to systematically test the influence of key rheological parameters (yield-curve ellipse aspect ratio, tensile strength, and ice strength) in sustaining fast ice. To support this, we introduce a new grounded iceberg dataset and a method to prescribe realistic grounded iceberg distributions based on observations. Our results show that the model reproduces the observed spatial distribution, seasonal maximum, and growth and retreat rates of Antarctic fast ice. Simulated fast ice reproduces the observed seasonal climatology but captures only limited inter-annual variability in circum-Antarctic fast-ice area. We demonstrate that simulated fast ice is highly sensitive to the ellipse aspect ratio (controlling the shear strength of the yield curve), tensile strength magnitude, and the presence and distribution of grounded icebergs. Realistic Antarctic fast ice is produced with an ellipse aspect ratio of 1.2, a tensile strength of 0.2, and a prescribed pan-Antarctic grounded iceberg extent of ~580 grid cells distributed consistently with observations. In this configuration, comparison with an otherwise similar simulation without grounded icebergs indicates that approximately 83 % of simulated fast-ice area depends on grounded icebergs as mechanical anchoring points. Importantly, these rheology and grounded iceberg modifications do not degrade the simulation of overall sea-ice area, thickness, or velocity in the Southern Ocean in our stand-alone simulations. These findings provide practical guidance for improving Antarctic fast-ice representation in coupled climate models through realistic grounded iceberg representation and targeted tuning of rheological parameters.

Identifying the full suite of processes that drive the melting of Antarctic sea ice each summer is crucial to improving the currently-poor ability of contemporary models to accurately simulate the climatological retreat phase of the annual sea-ice cycle. This is critical to (1) understanding and attributing observed trends and recent abrupt changes in sea-ice coverage and (2) the more robust prediction of future sea-ice conditions and impacts. This paper identifies wave-driven processes that can accelerate the seasonal melting of sea ice both in the marginal ice zone (MIZ) and in open-water areas within the interior sea-ice zone (SIZ). It builds on the long-held view that seasonal Antarctic sea-ice ablation is primarily driven by ice-floe lateral and basal melting enhanced in the MIZ by wave breakup of ice floes, by demonstrating that ocean waves play important additional roles in generating surface and interior melting (termed “wave melting”) via three sets of processes: “wave flooding”, “wave pulverisation”, and “wave greening” (involving algal proliferation in wave-modified ice). Based on existing observations and simple one-dimensional modelling, these wave processes are estimated to reduce ice albedo by 0.38–0.64 compared to snow-covered ice, resulting in vertical melt-rate enhancements of 0.9–5.2 cm d⁻¹ amplified by wave greening to 1.1–6.1 cm d⁻¹. The study also identifies five positive feedback and sub-feedback mechanisms that likely accelerate the ice melting further. It addresses a gap in current climate and Earth system models, which account for wave effects on floe-size distributions but overlook these coupled wave-driven dynamic, thermodynamic and biological processes that may contribute to explaining why and how Antarctic sea ice can melt back so rapidly each summer. An intention of this foundational study is to stimulate further targeted investigation aimed at quantifying the role of wave melting in the annual sea-ice cycle – as well as the contribution of wave greening to primary production in the sea-ice zone and its role in key biogeochemical processes that feed back to climate. The work has implications for planetary albedo, global climate feedbacks, marine ecosystems, and the accuracy of future sea-ice and climate projections in an increasingly-stormy Southern Ocean, as well as in a changing Arctic.