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Ice cores provide a record of changes in dust flux to Antarctica, which is thought to reflect changes in atmospheric circulation and environmental conditions in dust source areas^,,,,,,,,. Isotopic tracers suggest that South America is the dominant source of the dust^,,, but it is unclear what led to the variable deposition of dust at concentrations 20–50 times higher than present in glacial-aged ice^,. Here we characterize the age and composition of Patagonian glacial outwash sediments, to assess the relationship between the Antarctic dust record from Dome C (refs , ) and Patagonian glacial fluctuations^,, for the past 80,000 years. We show that dust peaks in Antarctica coincide with periods in Patagonia when rivers of glacial meltwater deposited sediment directly onto easily mobilized outwash plains. No dust peaks were noted when the glaciers instead terminated directly into pro-glacial lakes. We thus propose that the …