The tale of two ice shelves: Zachariae Isstrøm and Nioghalvfjerdsfjorden, Northeast Greenland

Oceanography and gravity data of Northeastern Greenland reveal ocean temperature and bathymetry in front of Zachariae Isstrøm (ZI) and Nioghalvfjerdsfjorden (79N), which hold a 1.1-m sea-level rise ice volume equivalent but underwent different evolutions. Sub-surface, warm, salty water of Atlantic origin has easier access to ZI than to 79N because of bathymetric barriers. We reconstruct ice removal by the ocean at the grounding line and floatation retreat from thinning to explain the observed grounding line retreat since 1979. The agreement between observed and calculated retreat demonstrates that ocean thermal forcing is a major control on the glacier evolution and undercutting of grounded ice must be included in numerical ice sheet models to reproduce the high rates of retreat.