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Warmer ocean conditions could impact future ice loss from Antarctica due to their ability to thin and reduce the buttressing of laterally confined ice shelves. Previous studies highlight the potential for a cold to warm ocean regime shift within the sub-shelf cavities of the two largest Antarctic ice shelves - the Filchner–Ronne and Ross. However, how this impacts upstream ice flow and mass loss has not been quantified. Here using an ice sheet model and an ensemble of ocean-circulation model sub-shelf melt rates, we show that transition to a warm state in those ice shelf cavities leads to a destabilization and irreversible grounding line retreat in some locations. Once this ocean shift takes place, ice loss from the Filchner–Ronne and Ross catchments is greatly accelerated, and conditions begin to resemble those of the present-day Amundsen Sea sector - responsible for most current observed Antarctic ice loss - where this thermal shift has already occurred.

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Ice loss from the grounded regions of the Antarctic ice sheet is impacted by changes in the thickness and extent of the adjoining floating ice shelves, due to their capacity to buttress ice flow inland1,2. Mass loss from the Antarctic ice sheet has accelerated in recent decades3, and some of the recently observed ice loss has been related to a reduction in ice shelf buttressing caused by ocean-induced ice shelf thinning4. Current ice loss is primarily concentrated in the Amundsen Sea Embayment region of West Antarctica3,5. Uniquely, ice shelf cavities in this region are in partial contact with relatively warm deep water (for example, ref. 6), whereas many other ice shelves, in particular the large Filchner–Ronne and Ross, are in contact with comparatively colder water masses. Several previous ocean modelling studies have now shown the potential for near-future (on the order of decades) thermal regime shifts whereby intrusions of warm deep water replace the currently cold shelf waters w