| Summary: | Totten Glacier, the primary ice discharger of the East Antarctic Ice Sheet (EAIS), contains 3.85 m sea level rise equivalent ice mass (SLRe) and has displayed dynamic change driven by interaction of its ice shelf with the Southern Ocean. To project Totten Glacier's evolution, it is critical that sub-shelf ocean processes are properly resolved in dynamic ice sheet models. First, we combine an ocean box model with a buoyant plume parameterization to create PICOP, a novel melt parameterization that resolves sub-shelf vertical overturning and produces melt rates that are in excellent agreement with observations. We then use this parameterization to make century-scale mass balance projections of the EAIS, forced by surface mass balance and ocean thermal anomalies from ten global climate models. Although increased snowfall offsets ice discharge in high emission scenarios and results in ~10 mm SLRe gain by 2100, significant grounded ice thinning (1.15 m/yr) and mass loss (~6 mm SLRe) from Totten Glacier is projected. To investigate whether PICOP misses important processes, such as the advection of warm water into the ice shelf cavity, we develop a fully coupled ice-ocean model and find that warm water is able to access Totten Glacier's sub-shelf cavity through topographic depressions along the central and eastern calving front. By mid-century in high emission scenarios, warm water intrusions become strong enough to overcome topographic barriers and dislodge Totten Glacier's southern grounding line, triggering abrupt acceleration in ice discharge (+185%). Overall, the timing and extent of Totten Glacier's retreat is predominately controlled by the sub-shelf ocean circulation, highlighting the importance of studying dynamic glaciers in fully coupled ice-ocean models.
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