The 79 North Glacier (79NG) in Northeast Greenland features the largest floating ice tongue in the region. Despite its extent remaining relatively stable, observations indicate significant thinning of the ice tongue from below, potentially due to ocean warming and increased subglacial discharge. A global simulation using the Finite-volume Sea-ice–Ocean Model (FESOM2.1) with a 700 m resolution resolves the ocean circulation in the cavity and disentangles the impact of ocean and atmosphere. The study finds that interannual variability in basal melt under 79NG over the past 50 years is primarily driven by changes in the temperature of the Atlantic Intermediate Water (AIW) inflow, which can be traced back to the eastern Fram Strait with a lag of 3 years. The AIW temperature increased by 0.8°C from the 1970s to the 2010s, leading to a quadratic dependency of basal melt on AIW temperature. Subglacial discharge, contributing about 20% of the freshwater input to the cavity, also plays a role, with a square-root dependency on basal melt. The study suggests that ocean warming is the dominant driver of basal melt, while subglacial discharge may become more significant in the future due to increased runoff from the Greenland Ice Sheet.The 79 North Glacier (79NG) in Northeast Greenland features the largest floating ice tongue in the region. Despite its extent remaining relatively stable, observations indicate significant thinning of the ice tongue from below, potentially due to ocean warming and increased subglacial discharge. A global simulation using the Finite-volume Sea-ice–Ocean Model (FESOM2.1) with a 700 m resolution resolves the ocean circulation in the cavity and disentangles the impact of ocean and atmosphere. The study finds that interannual variability in basal melt under 79NG over the past 50 years is primarily driven by changes in the temperature of the Atlantic Intermediate Water (AIW) inflow, which can be traced back to the eastern Fram Strait with a lag of 3 years. The AIW temperature increased by 0.8°C from the 1970s to the 2010s, leading to a quadratic dependency of basal melt on AIW temperature. Subglacial discharge, contributing about 20% of the freshwater input to the cavity, also plays a role, with a square-root dependency on basal melt. The study suggests that ocean warming is the dominant driver of basal melt, while subglacial discharge may become more significant in the future due to increased runoff from the Greenland Ice Sheet.