Mass loss from the Greenland ice sheet has contributed to global sea-level rise over the past 20 years. Yet direct observations from the 79 North Glacier (79NG) calving front reveal decreasing Atlantic Intermediate Water (AIW) temperatures below the ice tongue from 2018 to 2021, leading to reduced ocean heat transport. This is linked to a concurrent decrease in basal melt and thinning rates at the grounding line. The origin of this AIW cooling is traced to a slowdown of the large-scale ocean circulation in the Nordic Seas, driven by European atmospheric blocking that strengthens cold air advection from the central Arctic through the Fram Strait. Blocking has driven major ocean cooling events over the last 50 years and will remain crucial in affecting Northeast Greenland's glaciers.