Timing and drivers of Patagonian Ice Sheet variability during the last glacial cycle

During the Last Glacial Maximum (23,000 to 19,000 years ago), the Patagonian Ice Sheet (PIS) covered much of the southern Andes between 38°S and 55°S, representing the largest ice mass in the Southern Hemisphere mid-latitudes. Geological evidence from Patagonia and New Zealand indicates that maximum ice extent was not synchronous with Northern Hemisphere ice-sheet evolution. Here we present transient numerical simulations of the Patagonian Ice Sheet spanning the entire Last Glacial Cycle.

Our results reveal two major phases of ice-sheet expansion, during Marine Isotope Stage 4 and late Marine Isotope Stage 3, superimposed by pronounced inter-millennial-scale variability. These high-frequency fluctuations are consistent with Southern Hemisphere climate variability and exerted a first-order control on the timing and magnitude of ice advances, particularly during intermediate glacial states. Long-term evolution of the PIS is closely linked to changes in integrated summer insolation. This metric combines summer duration and insolation intensity and exhibits an obliquity-like periodicity. This forcing provides a robust explanation for the timing and magnitude of major ice advances. We further suggest that integrated summer insolation played a broader role in modulating glacier behaviour across the Southern Hemisphere mid-latitudes, offering a unifying framework to interpret asynchronous glacial variability between hemispheres.