Chen Zhao

Subglacial freshwater discharge plays a critical role in modulating basal melting and ocean circulation beneath ice shelves, yet the combined influence of discharge configuration, cavity thermal state, and sediment-driven morphodynamics remains poorly constrained. Using idealised ocean simulations following the ISOMIP+ framework, we investigate how subglacial discharge location, configuration (channelised versus distributed), and sediment load interact with contrasting warm and cold cavity regimes, and how these processes influence the circulation, melt, and seabed evolution at the grounding zone. Melt rates differ markedly between warm and cold regimes, with values in the warm cavity an order of magnitude higher than in the cold cavity. However, relative to no-discharge control experiments, subglacial discharge induces substantially greater local melt anomalies at the grounding line in the cold cavity, where localised melt rate increases up to ~955 %, compared to ~173 % in the warm regime. Discharge location and configuration further control the spatial extent of the response, with channelised inputs driving strong, localised melting, and distributed inputs producing weaker but more spatially extensive melt across the grounding zone. Sediment-laden subglacial discharge consistently reduces localised melt under channelised configurations (~13 % reduction in the warm regime and ~16 % in the cold regime), whereas its influence is negligible (<1 %) when discharge is distributed. These reductions arise primarily through morphodynamic feedbacks, as sediment modifies seabed structure and circulation near the grounding zone. In the cold regime, reduced circulation promotes sediment accumulation and episodic erosion, leading to seabed and circulation changes. These results demonstrate that the impact of subglacial discharge on basal melt depends on the combined effects of cavity regime, discharge configuration, and sediment dynamics, with implications for representing grounding zone processes and basal melt parametrisations in ice-ocean models, and ultimately for ice shelves vulnerability and Antarctic Ice Sheet stability.

Subglacial freshwater discharge plays a critical role in modulating basal melting and ocean circulation beneath ice shelves, yet the combined influence of discharge configuration, cavity thermal state, and sediment-driven morphodynamics remains poorly constrained. Using idealised ocean simulations following the ISOMIP+ framework, we investigate how subglacial discharge location, configuration (channelised versus distributed), and sediment load interact with contrasting warm and cold cavity regimes, and how these processes influence the circulation, melt, and seabed evolution at the grounding zone. Melt rates differ markedly between warm and cold regimes, with values in the warm cavity an order of magnitude higher than in the cold cavity. However, relative to no-discharge control experiments, subglacial discharge induces substantially greater local melt anomalies at the grounding line in the cold cavity, where localised melt rate increases up to ~955 %, compared to ~173 % in the warm regime. Discharge location and configuration further control the spatial extent of the response, with channelised inputs driving strong, localised melting, and distributed inputs producing weaker but more spatially extensive melt across the grounding zone. Sediment-laden subglacial discharge consistently reduces localised melt under channelised configurations (~13 % reduction in the warm regime and ~16 % in the cold regime), whereas its influence is negligible (<1 %) when discharge is distributed. These reductions arise primarily through morphodynamic feedbacks, as sediment modifies seabed structure and circulation near the grounding zone. In the cold regime, reduced circulation promotes sediment accumulation and episodic erosion, leading to seabed and circulation changes. These results demonstrate that the impact of subglacial discharge on basal melt depends on the combined effects of cavity regime, discharge configuration, and sediment dynamics, with implications for representing grounding zone processes and basal melt parametrisations in ice-ocean models, and ultimately for ice shelves vulnerability and Antarctic Ice Sheet stability.

Exceeding the 1.5 °C Paris Agreement limit is now unavoidable, raising a critical question: how does the overshoot duration affect Antarctica's contribution to sea-level rise? Here we use an ice-sheet model to compare scenarios in which high-emissions forcing (SSP3-7.0) persists for 20, 50, 75 or 100 years before returning towards a low-emissions pathway (SSP1-2.6). When atmospheric and ocean forcing recover together, the additional contribution relative to sustained low forcing remains below 3 mm sea-level equivalent (SLE) by 2300 after 20-50 years of high forcing, but increases nonlinearly to 8.6 and 21.5 mm SLE after 75 and 100 years, respectively. When atmospheric and ocean forcing both recover after 50 years of high forcing, the additional contribution is only 2.3 mm SLE. However, this contribution increases to 44.1 mm SLE when ocean forcing is kept high for a further 50 years, in line with expectations of delayed ocean recovery, even while atmospheric forcing declines. Thus, shortening the overshoot duration limits Antarctica's additional contribution to sea-level rise, but the benefit depends strongly on how quickly ocean temperature declines.

The Antarctic Ice Sheet is the largest source of uncertainty in sea-level rise projections, with uncertainties propagating through emissions scenarios, atmosphere–ocean general circulation models, ice-sheet dynamics and sea-level physics. In ice-sheet model intercomparison exercises, these uncertainties—typically attributed to intermodel differences—stem from modelling choices that may bias ensembles towards commonly adopted approaches regardless of observational consistency. Here we quantify how each individual physical assumption cascades into projection uncertainty using a machine-learning emulation framework, which also enables Bayesian calibration against satellite observations to reduce projection bias. Our results suggest it is very likely (≥0.92 probability) that the Antarctic Ice Sheet is committed to twenty-first-century mass loss, even under aggressive emissions-reduction scenarios. Higher emissions drive greater Antarctic mass loss by 2100 (≥0.89 probability), directly elevating near-term coastal risks. Under very high-emissions scenarios, we identify cascading mechanisms that could produce up to 25.4 cm of sea-level rise by 2100 (95th percentile; median = 15.7 cm) while remaining consistent with satellite observations. Effective management of these risks to densely populated coastal communities requires rapid emissions reductions and improved constraints on climate model selection, sliding laws and ice-shelf melt parameterizations.

Subglacial freshwater discharge plays a critical role in modulating basal melting and ocean circulation beneath ice shelves, yet the combined influence of discharge configuration, cavity thermal state, and sediment-driven morphodynamics remains poorly constrained. Using idealised ocean simulations following the ISOMIP+ framework, we investigate how subglacial discharge location, configuration (channelised versus distributed), and sediment load interact with contrasting warm and cold cavity regimes, and how these processes influence the circulation, melt, and seabed evolution at the grounding zone. Melt rates differ markedly between warm and cold regimes, with values in the warm cavity an order of magnitude higher than in the cold cavity. However, relative to no-discharge control experiments, subglacial discharge induces substantially greater local melt anomalies at the grounding line in the cold cavity, where localised melt rate increases up to ~955 %, compared to ~173 % in the warm regime. Discharge location and configuration further control the spatial extent of the response, with channelised inputs driving strong, localised melting, and distributed inputs producing weaker but more spatially extensive melt across the grounding zone. Sediment-laden subglacial discharge consistently reduces localised melt under channelised configurations (~13 % reduction in the warm regime and ~16 % in the cold regime), whereas its influence is negligible (<1 %) when discharge is distributed. These reductions arise primarily through morphodynamic feedbacks, as sediment modifies seabed structure and circulation near the grounding zone. In the cold regime, reduced circulation promotes sediment accumulation and episodic erosion, leading to seabed and circulation changes. These results demonstrate that the impact of subglacial discharge on basal melt depends on the combined effects of cavity regime, discharge configuration, and sediment dynamics, with implications for representing grounding zone processes and basal melt parametrisations in ice-ocean models, and ultimately for ice shelves vulnerability and Antarctic Ice Sheet stability.

Subglacial freshwater discharge plays a critical role in modulating basal melting and ocean circulation beneath ice shelves, yet the combined influence of discharge configuration, cavity thermal state, and sediment-driven morphodynamics remains poorly constrained. Using idealised ocean simulations following the ISOMIP+ framework, we investigate how subglacial discharge location, configuration (channelised versus distributed), and sediment load interact with contrasting warm and cold cavity regimes, and how these processes influence the circulation, melt, and seabed evolution at the grounding zone. Melt rates differ markedly between warm and cold regimes, with values in the warm cavity an order of magnitude higher than in the cold cavity. However, relative to no-discharge control experiments, subglacial discharge induces substantially greater local melt anomalies at the grounding line in the cold cavity, where localised melt rate increases up to ~955 %, compared to ~173 % in the warm regime. Discharge location and configuration further control the spatial extent of the response, with channelised inputs driving strong, localised melting, and distributed inputs producing weaker but more spatially extensive melt across the grounding zone. Sediment-laden subglacial discharge consistently reduces localised melt under channelised configurations (~13 % reduction in the warm regime and ~16 % in the cold regime), whereas its influence is negligible (<1 %) when discharge is distributed. These reductions arise primarily through morphodynamic feedbacks, as sediment modifies seabed structure and circulation near the grounding zone. In the cold regime, reduced circulation promotes sediment accumulation and episodic erosion, leading to seabed and circulation changes. These results demonstrate that the impact of subglacial discharge on basal melt depends on the combined effects of cavity regime, discharge configuration, and sediment dynamics, with implications for representing grounding zone processes and basal melt parametrisations in ice-ocean models, and ultimately for ice shelves vulnerability and Antarctic Ice Sheet stability.

Understanding the coastal zone of the Antarctic Ice Sheet (AIS), where it interacts with the Southern Ocean and warmer air masses, is crucial for predicting Antarctica's influence on the global climate and sea level. This region has multiple tipping mechanisms that could trigger large, rapid, and potentially irreversible changes in the AIS, the Southern Ocean and their global connections in the coming centuries. The AIS remains the largest source of uncertainty in future sea‐level projections. Bed topography beneath the ice shelves and the coastal ice sheet is not yet well documented, and is a major source of this uncertainty. This review assesses current knowledge of the coastal zone and highlights methods to investigate it, including aerogeophysical surveys, ground‐ and ship‐based measurements, satellite observations, and computer modeling. An ensemble analysis of published bed topography data sets identifies significant data gaps and their regional distribution, framed in the context of current ice‐sheet behavior and potential instability. We propose scientific priorities and guidelines for future aerogeophysical surveys, advocating for a comprehensive, coordinated international effort to build a next‐generation data set of Antarctic bed properties. Such an initiative would significantly advance understanding of the role of coastal processes in ice‐sheet dynamics, reducing uncertainties in sea‐level rise projections and improving predictions of future ocean and climate changes.

Subglacial freshwater discharge plays a critical role in modulating basal melting and ocean circulation beneath ice shelves, yet the combined influence of discharge configuration, cavity thermal state, and sediment-driven morphodynamics remains poorly constrained. Using idealised ocean simulations following the ISOMIP+ framework, we investigate how subglacial discharge location, configuration (channelised versus distributed), and sediment load interact with contrasting warm and cold cavity regimes, and how these processes influence the circulation, melt, and seabed evolution at the grounding zone. Melt rates differ markedly between warm and cold regimes, with values in the warm cavity an order of magnitude higher than in the cold cavity. However, relative to no-discharge control experiments, subglacial discharge induces substantially greater local melt anomalies at the grounding line in the cold cavity, where localised melt rate increases up to ~955 %, compared to ~173 % in the warm regime. Discharge location and configuration further control the spatial extent of the response, with channelised inputs driving strong, localised melting, and distributed inputs producing weaker but more spatially extensive melt across the grounding zone. Sediment-laden subglacial discharge consistently reduces localised melt under channelised configurations (~13 % reduction in the warm regime and ~16 % in the cold regime), whereas its influence is negligible (<1 %) when discharge is distributed. These reductions arise primarily through morphodynamic feedbacks, as sediment modifies seabed structure and circulation near the grounding zone. In the cold regime, reduced circulation promotes sediment accumulation and episodic erosion, leading to seabed and circulation changes. These results demonstrate that the impact of subglacial discharge on basal melt depends on the combined effects of cavity regime, discharge configuration, and sediment dynamics, with implications for representing grounding zone processes and basal melt parametrisations in ice-ocean models, and ultimately for ice shelves vulnerability and Antarctic Ice Sheet stability.