Accelerating ice loss from Antarctica's ice sheets is projected to contribute 13-42 cm of sea level rise by the end of the century (Edwards et al., 2021). This contribution is mainly driven by an increase in ice flowing off the continent and into the ocean. Most Antarctic ice discharge becomes part of a floating ice shelf (Rignot et al., 2013), half of which will melt before it reaches the open ocean, while the other half will eventually calve as icebergs (Liu et al., 2015;Rignot et al., 2013). Ice shelves slow the discharge of glacial ice into the ocean. When ice shelves drag past coastlines, islands, and pinning points, they generate back stresses and buttress against ice flow (e.g., Dupont & Alley, 2005;Fürst et al., 2016). This buttressing is an important control on the rate of ice loss from Antarctica. The removal of buttressing when an ice shelf retreats or disintegrates leads to the acceleration of ice loss (e.g., Berthier et al., 2012;Rignot et al., 2004;Scambos et al., 2004).Melt at the base of ice shelves is largely controlled by ocean circulation in the sub-ice-shelf cavity. Theoretical frameworks of ocean circulation under ice shelves were first developed from the interpretation of direct oceanographic observations at ice shelf fronts (e.g., S. S. Jacobs et al., 1979). At a large scale, currents under an ice shelf follow a circulation-cell, described in detail by S. Jacobs et al. (1992) and well approximated by the ice pump mechanism (Lewis & Perkin, 1986). Sea ice formation releases high salinity water which sinks and flows down-