The ice streams flowing into the Amundsen Sea, West Antarctica, are
losing mass due to changes in the oceanic basal melting of their
floating ice shelves. Rapid ice-shelf melting is sustained by the
delivery of warm Circumpolar Deep Water to the ice-shelf cavities, which
is first supplied to the continental shelf by an undercurrent that flows
eastward along the shelf break. Temporal variability of this
undercurrent controls ice-shelf basal melt variability. Recent work
shows that on decadal timescales the undercurrent variability opposes
surface wind variability. Using a regional model, we show that
undercurrent variability is driven by sea-ice freshwater fluxes,
particularly those north of the shelf break, which affect the
cross-shelf break density gradient. This sea-ice variability is caused
by tropical Pacific variability impacting atmospheric conditions over
the Amundsen Sea. Ice-shelf melting also feeds back onto the
undercurrent by affecting the on-shelf density, thereby influencing
shelf-break density gradient anomalies.