An eddy‐resolving coupled regional ocean‐sea ice‐ice shelf model is employed to locate the hot spots where modified Circumpolar Deep Water (mCDW) intrudes onto the continental shelf within Prydz Bay, and locate the paths through which mCDW is transported to the Amery Ice Shelf (AIS) calving front. Evaluation of the model output is with satellite, hydrographic and borehole data. Two critical windows responsible for mCDW intrusions are identified. The first is the eastern branch of the cyclonic Prydz Bay gyre (PBG) that carries mCDW to the ice front line, accounting for an annual mean heat transport of ∼8.7 ×10¹¹ J s⁻¹. The second is located to the east of the Four Ladies Bank (FLB) where mCDW is channeled through submarine troughs, accounting for an annual mean heat transport of ∼16.2 ×10¹¹ J s⁻¹. The eddy‐induced heat transport accounts for ∼23% in the path of the PBG and ∼52% in the path of the eastern coastal current, with respect to their total onshore heat transport. The seasonal pulsing of mCDW intrusions is greatly dependent on the seasonal cycle of the Antarctic Slope Current (ASC) that peaks with a maximum of ∼29.3 Sv at 75°E in June. In austral winter, mCDW is allowed to access the eastern flank of the AIS calving front with potential consequences for the basal mass balance of the AIS. The dynamic effects of small‐scale troughs on the longshore ASC play an important role in the onshore mCDW transport.

Analyses of hydrographic observation data sets revealed that modified Circumpolar Deep Water (mCDW) tends to flood the western flank (73–78°E, 67–68°S) of the Four Ladies Bank (FLB) in Prydz Bay. In this study, we investigated the mechanism responsible for mCDW upwelling over the FLB based on an eddy‐resolving coupled ocean‐sea ice‐ice shelf model in conjunction with the latest high‐accuracy bathymetry. It was found that zonal step‐like declines in the seabed over the FLB are crucial for the mCDW onshore upwelling, through topographic dynamic effects on the alongshore Antarctic Slope Current. In the presence of meridional cross‐shelf σ_θ isopycnals, warm mCDW at ~500‐m depth in the deep sea can make its approach to the shallower continental shelf (~200‐ to 500‐m depths), characterized as a warm layer (> −1.8 °C) bounded by the cross‐shelf σ_θ isopycnal surfaces of 27.5 and 27.7 kg/m³. The simulated outflow of the Prydz Bay gyre is concentrated to the eastern flank of the Prydz Channel. These results suggest that, in addition to the depressions and troughs around the Antarctic, smaller topographic features such as step‐like declines in the seabed near the Antarctic Slope Current are also favorable for onshore mCDW intrusion. This study demonstrates that mCDW onshore transport around the Antarctic continental shelf might be significantly underestimated by numerical models with coarse spatial representations of the topography.

The bathymetry around Antarctica can govern the shelf sea circulations and play a key role in conditioning water masses. In Prydz Bay, the Prydz Bay Gyre and coastal currents are also determined by the continental shelf topography. However, due to the paucity of beam echo sounding data, the bathymetric datasets in Prydz Bay still have large uncertainties. With the aid of in situ hydrographic observations, this study focuses on the correction of an up-to-date bathymetric dataset and the resultant influences on the shelf circulation and the basal melting of the ice shelves. The corrected bathymetry mainly improves the biased shallow representations in the uncorrected bathymetric data set, with a maximum change of ~500 m deepening in the eastern flank of Prydz Bay. Sensitivity numerical experiments show that the bathymetric corrections in Prydz Bay have a significant impact on the circulation pattern and onshore warm water intrusions. In addition, the corrected bathymetry markedly decreases the heat transport towards the calving front of the Amery Ice Shelf. The onshore heat transport reduces by ~22.18% from ~5.23×10¹³ J s^-1 to ~4.07×10¹³ J s^-1 over the outer shelf. Over the inner shelf, the heat transport towards the Amery Ice Shelf reduces by ~18.15% from ~5.95×10¹³ J s^-1 to ~4.87×10¹³ J s^-1. Consequently, the temporally and spatially averaged basal melting rate of the Amery Ice Shelf reduces by ~13.04% from ~0.69 m yr^-1 to ~0.60 m yr^-1.

The extreme Arctic sea ice minima in the twenty-first century have been attributed to multiple factors, such as anomalous atmospheric circulation, excess solar radiation absorbed by open ocean, and thinning sea ice in a warming world. Most likely it is the combination of these factors that drives the extreme sea ice minima, but how the factors rank in setting the conditions for these events has not been quantified. To address this question, the sea ice budget of an Arctic regional sea ice–ocean model forced by atmospheric reanalysis data is analyzed to assess the development of the observed sea ice minima. Results show that the ice area difference in the years 2012, 2019, and 2007 is driven to over 60% by the difference in summertime sea ice area loss due to air–ocean heat flux over open water. Other contributions are small. For the years 2012 and 2020 the situation is different and more complex. The air–ice heat flux causes more sea ice area loss in summer 2020 than in 2012 due to warmer air temperatures, but this difference in sea ice area loss is compensated by reduced advective sea ice loss out of the Arctic Ocean mainly caused by the relaxation of the Arctic dipole. The difference in open water area in early August leads to different air–ocean heat fluxes, which distinguishes the sea ice minima in 2012 and 2020. Further, sensitivity experiments indicate that both the atmospheric circulation associated with the Arctic dipole and extreme storms are essential conditions for a new low record of sea ice extent.

Persistent outflow of supercooled ice-shelf water (ISW) from beneath McMurdo Ice Shelf creates a rapidly growing sub-ice platelet layer (SIPL) with a unique crystallographic structure under the sea ice in McMurdo Sound, Antarctica. A vertically modified frazil-ice-laden ISW plume model that encapsulates the combined non-linear effects of the vertical distributions of supercooling and frazil concentration on frazil-ice growth is applied to McMurdo Sound and is shown to reproduce the observed ISW supercooling and SIPL distributions. Using this model, the dependence of the SIPL thickening rate and depth-averaged frazil-ice concentration on ISW supercooling in McMurdo Sound is investigated and found to be predominantly controlled by the vertical distribution of frazil concentration. The complex dependence on frazil concentration highlights the need to improve frazil-ice observations within the sea-ice–ocean boundary layer in McMurdo Sound.