Melt rates of West Antarctic ice shelves in the Amundsen Sea track large
decadal variations in the volume of warm water at their outlets. This
variability is generally attributed to wind-driven variations in warm
water transport towards ice shelves. Inspired by conceptual
representations of the global overturning circulation, we introduce a
simple model for the evolution of the thermocline, which caps the water
warm layer at the ice-shelf front. This model demonstrates that
interannual variations in coastal polynya buoyancy forcing can generate
large decadal-scale thermocline depth variations, even when the supply
of warm water from the shelf-break is fixed. The modeled variability
involves transitions between bistable high and low melt regimes, enabled
by feedbacks between basal melt rates and ice front stratification
strength. Our simple model captures observed variations in near-coast
thermocline depth and stratification strength, and poses an alternative
mechanism for warm water volume changes to wind-driven theories.