Ice-sheet evolution controlled by meltwater connectivity across ice-shelf gaps

Abstract. In regions of intense sub-shelf melting, ice shelves can substantially weaken, potentially leading to the formation of gaps within the ice shelf. Using a coupled ice-sheet–meltwater-layer model, we investigate two end-member representations of meltwater transport across such gaps: meltwater either exits the cavity (sink) or remains dynamically connected across ice-free regions (connected). For an idealised ice-sheet–ice-shelf geometry based on the MISMIP+ framework, our results show that gaps form under both moderate (0 °C at depth) and warm (1 °C at depth) ocean forcing, driven by enhanced melting associated with a strong western boundary current. When gaps are treated as sinks, downstream melting is suppressed. In contrast, retaining meltwater connectivity allows heat and momentum to propagate downstream, enhancing further ice-shelf thinning along the western shear margin. This thinning reduces stress transmission between the ice shelf and the grounded ice, resulting in greater ice-volume loss in the connected configuration. The difference in ice-volume loss between the two meltwater representations can be comparable in magnitude to that caused by a 1 °C increase in ocean temperature forcing. These results highlight meltwater connectivity across ice-shelf gaps as an important source of uncertainty in projections of ice-sheet evolution and mass loss.