Rapid thinning of the Cordillera Darwin Icefield at the onset of Termination I

Despite more than a century of research, the cause of the last ice-age termination remains uncertain. Here, we reconstruct the thinning history of the Cordillera Darwin Icefield, southernmost Chile, to track relative summer temperature change at the end of the ice age and to explore potential drivers of the warming. Eighteen ¹⁰Be exposure ages of erratics perched on glacially scoured bedrock indicate rapid surface lowering of at least 500 m elevation in the heart of the former icefield at some time between 18.8 and 16.9 ka at the onset of the termination. We infer that this drop in ice level reflects an increase in summer temperatures, which led to extensive glacier melt. We attribute the underlying cause to a poleward shift of the southern westerly winds, which placed the Cordillera Darwin Icefield in warmer air masses with temperatures incompatible with its LGM extent.