Understanding the driving processes at stake for the Circumpolar Deep Water (CDW) intrusion onto the Amundsen shelf is crucial. We use a multi-decadal ocean simulation at 1/12° to revisit the ocean dynamics at the Amundsen shelf break, distinguishing a western fresh shelf and an eastern warm shelf. While the prevailing presence of the Antarctic Slope Current - fed to the east of Russel Bay through vortex stretching of an outflow of melted waters - blocks CDW intrusions in the west, the contact of Antarctic Circumpolar Current (ACC) branches along the shelf in the east favors this inflow. Of particular importance is a southern ACC branch initiated to the south-east of the Ross Gyre, which interacts with the topography at the entry of the western Pine Island-Thwaites trough. Then, we link the ocean interannual-to-decadal variability at the shelf break with the ice-shelf basal melting and create a Fresh-Warm Boundary Index (FWBI) to follow the oscillation of the fresh-warm shelves limit through time in Russel Bay, which could be a focal point to understand the low frequency fluctuations of the basal melt. We suggest that not only a wind-induced Ekman pumping could favor the CDW inflow at the shelf break, but also topographic interactions, a bottom Ekman transport, a sea-ice–induced Ekman pumping resulting from strong surface currents, and the baroclinicity of the eastward along-shelf current in the west. Finally, we highlight that El Niño-Southern Oscillation has no strong correlation with the ice-shelf basal melt variability, except for the very recent years.