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Evidence from radiocarbon dating and complex ice sheet modeling suggests that the fastest rate of sea level rise in Earth's recent history coincided with collapse of the ice saddle between the Laurentide and Cordilleran ice sheets during the last deglaciation. In this study, we derive a simple, two-equation model of two ice sheets intersecting in an ice saddle. We show that two conditions are necessary for producing the acceleration in ice sheet melt associated with meltwater pulses: the positive height-mass balance feedback and an ice saddle geometry. The amplitude and timing of meltwater pulses is sensitively dependent on the rate of climate warming during deglaciation and the relative size of ice sheets undergoing deglaciation. We discuss how simulations of meltwater pulses can be improved and the prospect for meltwater pulses under continued climate warming.

Plain Language Summary At the end of the last ice age, global sea levels rose by 10-20 m in period of less than 500 years. This was just one among many meltwater pulse events that are the fastest periods of sea level rise in Earth's recent history. Though the cause of these meltwater pulses is debated, observations and models suggest that they may be associated with the collapse of saddle regions at the junction of ice sheets. We show, using a simple mathematical model, that such meltwater pulses will occur in any ice sheet with a saddle region due to the rapid increase in the area and intensity of melting at the ice saddle surface during periods of climate warming. The size and timing of meltwater pulses depends on the rate of climate warming and the ice sheet geometry. We discuss how to better improve computer models of meltwater pulses and the possibility for a sudden acceleration in sea level rise in the future due to ice saddle collapse.