| 22 Oct 2026
From Melt-Limited Inception to Dynamically Supported Growth of the Laurentide Ice Sheet
Abstract. Glacial inception is commonly interpreted as a response to declining summer insolation, which reduces ablation and allows perennial snow to accumulate. How the controls on ice-sheet growth evolve after this initial phase, however, is less well understood. Here, we analyze a transient simulation of the last glacial inception from 127 to 65 ka using the AWI Earth System Model (AWI-ESM) coupled to the Parallel Ice Sheet Model (PISM) for the Northern Hemisphere domain. Our results show two stages of Laurentide Ice Sheet (LIS) growth. During the early phase (127–115 ka), glaciation is mainly associated with reduced summer melt and follows the southward migration of the summer 0 °C isotherm. After approximately 115 ka, this relationship changes and the ice sheet margin continues to advance into regions with negative surface mass balance. A decomposition of changes in local ice thickness indicates that dynamic mass redistribution from the interior to the margin supports this advance. Changes in LIS surface elevation are associated with changes in regional moisture transport and an increasing fraction of precipitation falling as snow over parts of the ice sheet help maintain a positive surface mass balance in the interior. Our simulation indicates a transition from early, climate-limited glaciation to dynamically supported growth, in which local climate conditions no longer determine ice-sheet advance. Although the timing and magnitude of this transition depend on the experimental setup, our results show how an evolving ice sheet can shift the relative roles of melt, accumulation, and ice dynamics during glacial inception.
Competing interests: At least one of the (co-)authors serves as editor for the special issue to which this paper belongs.
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