The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Water beneath Antarctic ice may change how quickly grounded ice slides toward the ocean, while warming ocean water can thin floating ice shelves and weaken their support. Both processes could affect sea-level rise, but they are distinct, and the largest figures in recent studies are conditional model results—not measurements of what Antarctica is losing today.
What is happening beneath Antarctica’s ice?
The phrase “last great unknown” is not a formal scientific term, and it does not identify one specific Antarctic feature. A plausible interpretation is the poorly observed environment under the ice sheet: its bed, the water that can collect there, and the way that water drains. Scientists have also studied a separate threat beneath floating ice shelves: warm ocean water entering their cavities.
These settings matter in different ways. Subglacial water is at the boundary between grounded ice and rock or sediment. Ocean water beneath an ice shelf is in contact with the shelf’s underside. Either process can influence how much grounded ice reaches the sea, but they should not be treated as one mechanism or one forecast.
Can water under Antarctica’s ice make it move faster?
It can. Meltwater produced by frictional heating as ice moves, and by geothermal heat from below, can collect and flow along the bed. The 2025 study by Chen Zhao and coauthors describes both distributed drainage—water spread through linked pathways—and channelized drainage, where it is concentrated in larger routes.
Recommended Free Tools
#1 Best Overall
Water pressure at the bed affects how firmly ice is pressed against its substrate. When pressure is high, the ice may be less firmly coupled to the bed, reducing friction and allowing faster basal sliding. Faster-moving grounded ice can deliver more ice toward the coast. The details depend on how water pressure and drainage vary across a basin, so “more water means faster ice everywhere” is not a reliable rule.
A key unknown is the actual distribution of effective pressure—the difference between the pressure exerted by the overlying ice and the water pressure beneath it. Zhao and coauthors say this distribution beneath the Antarctic Ice Sheet is not established by observations well enough to constrain basal sliding confidently. Their results also show that responses vary by basin.
Rank #2
What did the subglacial-water study project?
In a 2025 Nature Communications study, Zhao and coauthors used the Elmer/Ice Antarctic Ice Sheet model to explore basal-water assumptions over 2015–2300. In the model, including subglacial water amplified ice discharge by up to threefold and could add 2.2 metres to sea-level rise by 2300.
Those are outcomes under the study’s modeling assumptions, not observed discharge increases or a certain projection for sea level. The 2.2-metre figure is an additional modeled contribution in that study’s scenario; it is not a prediction that Antarctica will add that amount under all future conditions. The authors frame the broader issue as deeply uncertain because subglacial water is suspected to matter, but its impact remains unclear.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Is warm ocean water melting Antarctic ice shelves?
Ocean water can melt floating ice shelves from below. Shelves act as a partial brake on grounded ice flowing seaward; thinning or loss of that buttressing can let grounded ice discharge more readily. This is different from water at the ice-bed interface: the immediate effect is shelf thinning and a possible reduction in restraint on inland ice.
A 2024 Nature Climate Change study by Emily A. Hill, G. Hilmar Gudmundsson and David M. Chandler modeled a possible shift to a warmer ocean state in the cavities beneath the Filchner–Ronne and Ross ice shelves. In those simulations, cavity warming of 2 to 4 °C was associated with sub-shelf melt rates increasing by approximately an order of magnitude, and some grounding lines retreated irreversibly. These are scenario-specific model results, not observations of a present warm-state shift beneath those shelves.
Rank #4
The study’s starting point is important: the Filchner–Ronne and Ross catchments are not currently contributing significant sea-level rise, and the authors found no indication that this changes in the near future under current climate conditions. The modeled danger arises if the ocean cavities shift into a warmer regime. The timing varied with the ocean-model forcing, and the simulations simplified some processes; the authors called for coupled ice–ocean modeling to better constrain response timescales.
How do the two threats differ?
| Question | Subglacial water | Warm water beneath ice shelves |
|---|---|---|
| Where is the water? | At the bed beneath grounded ice. | In ocean cavities under floating ice shelves. |
| How can it affect ice loss? | By changing basal pressure, friction and sliding, which can alter ice discharge. | By thinning shelves and potentially reducing their buttressing of grounded ice. |
| What is the key uncertainty? | The observed distribution of effective pressure and how basal water drains. | Whether and when a warmer ocean regime develops in the modeled shelf cavities, and how the coupled ice–ocean system responds. |
| What do the cited studies establish? | A 2025 model finds substantially greater discharge under its subglacial-water assumptions; the result is not a measured present-day increase. | A 2024 model finds potentially severe effects after a warm-state shift; it does not report such a shift already occurring in these cavities. |
The modeled threefold amplification and 2.2-metre additional sea-level rise in the 2025 paper cannot be added to the 2024 paper’s warm-cavity results to create a combined projection. The studies examine different processes and scenarios, and neither establishes a uniform response across Antarctica.
What should readers take from the uncertainty?
Uncertainty here does not mean that the mechanisms are imaginary; it means that observations and models do not yet pin down their magnitude and timing well enough for a single confident number. For subglacial water, the unresolved basal conditions affect estimates of how fast ice may slide. For the shelf cavities, the severe modeled response depends on a transition to warmer ocean conditions whose timing is not settled by these simulations.
The clearest conclusion is therefore conditional: subglacial water could amplify Antarctic ice discharge, and a future warm-ocean shift could threaten the buttressing role of particular shelves. Neither finding, by itself, says that the most severe modeled outcome is underway now or applies equally to every Antarctic basin.
Quick Recap
Studies behind the findings
- Chen Zhao and coauthors, “Subglacial water amplifies Antarctic contributions to sea-level rise,” Nature Communications, published 7 April 2025.
- Emily A. Hill, G. Hilmar Gudmundsson and David M. Chandler, “Ocean warming as a trigger for irreversible retreat of the Antarctic ice sheet,” Nature Climate Change, published 20 September 2024.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
