Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum

Abstract The Northeast Greenland Ice Stream (NEGIS), the largest ice stream draining the Greenland Ice Sheet (GrIS), is losing mass at an accelerating rate due to atmospheric and ocean-driven melting. Holding the equivalent of 1.1–1.4 metres of sea-level rise, its collapse will have a significant impact on global sea levels making it crucial to understand the controls on its dynamic behaviour. The NEGIS retreated from the continental shelf edge by 21.6 ka BP, with this study confirming continued grounding line retreat to ~100 km from the shelf edge by 20.3 ka BP, earlier than previously reported. This early retreat was driven by warm Return Atlantic Water (RAW) and amplified by a retrograde seabed, which together drove initial grounding line retreat. The presence of a series of grounding zone wedges indicates a quasi-stable grounding line, which was fronted by an ice shelf. Grounding-line retreat took place between 20.3 and 15.2 ka BP. However, ice-shelf break up caused by enhanced sub-ice shelf melt rates driven by RAW ingression, coupled with surface thinning instigated by atmospheric warming during Greenland Interstadial I, triggered rapid retreat of the ice stream after 15.2 ka BP. Our findings confirm the dominant role of oceanic forcing in grounding line stability and ice-shelf break up.