How do fixed dunes provide evidence of past climate change?

Fixed dunes provide significant evidence of past climate change by demonstrating that regions currently characterized by subhumid or humid climates were once much more arid.1

These landforms consist of older dunes that have been immobilized by the growth of vegetation, such as grasslands or forests, in areas where active sand seas would otherwise require extremely low rainfall to form. The presence of these stabilized, rounded, and subdued dune patterns indicates that the environmental conditions necessary for active eolian (wind-driven) sand transport—typically associated with desert climates—previously extended far beyond the boundaries of modern arid zones.12

During the Pleistocene Epoch, for instance, intensified wind activity and peak aridity in subtropical deserts coincided with periods of maximum glaciation in the Northern Hemisphere. As climates shifted toward more humid or pluvial conditions, these once-active desert areas contracted, allowing vegetation to colonize and stabilize the dunes. Consequently, these fixed features serve as a geological record of historical fluctuations in global rainfall and aridity.312