The mechanisms by which heat is delivered to Antarctic ice shelves are a major source of uncertainty when assessing the response of the Antarctic ice sheet to climate change. Direct observations of the ice shelf-ocean interaction are extremely scarce, and present ice shelf-ocean models struggle to predict reason able melt rates. Our two years of data during 2010-2012 from three oceanic moorings below the Fimbul Ice Shelf in the eastern Weddell Sea show cold cavity waters, with average temperatures of less than 0.1 {degree sign}C above the surface freezing point. This suggests rather low basal melt rates, consistent with remote sensing based, steady state mass balance estimates in this sector of the Antarctic coast. Oceanic heat for basal melting is found to be sup-plied by two sources of warm water that enter below the ice: (i) eddy-like bursts of Modified Warm Deep Water accesses the cavity at depth during eight months of the record; and (ii) a seasonal inflow of warm, fresh surface water flushes parts of the ice base with temperatures above freezing, during late summer and fall. This interplay of processes implies that basal melting cannot simply be parameterized by coastal deep ocean temperatures, but is directly linked to both solar forcing at the surface as well as to coastal processes controlling deep ocean heat fluxes.