Variability in prevailing wind patterns during the Quaternary based on yardang morphology in the Qaidam Basin, China, and implications for climate change

Abstract:

The Qaidam Basin (QB) in the NE Tibetan Plateau provides an exceptional example of an aeolian landscape, comprised of wind-scoured bedrock, yardangs, and sand dunes. Yardangs are elongated ridges, eroded into bedrock, that have a blunt windward end and a leeward end that tapers in the direction of wind flow. A change in wind direction may truncate or overprint older yardangs with new landforms, or a drop-off in wind speed may halt erosion and provide time to develop a soil on the yardang surface. Analysis of 158 yardangs from Google Earth imagery reveals at least three generations of yardangs in the QB, which suggests great shifts in wind paths over time. In addition, 97 dunes were measured to assess present wind direction. The majority of the studied yardangs (n=104) were shaped by NW winds (mean azimuth 140°), consistent with present wind directions based on dune morphology and weather station data. A second generation of yardangs (n=42; mean azimuth 180°) does not align with the present wind regime, and is in places cut by modern landforms, in addition to exhibiting windward erosion from present winds. The oldest evidence for wind erosion is observed from “paleoyardangs” (n=12) that appear to be much older ridges that were buried and then re-exhumed. These paleoyardangs are aligned at roughly 100° and suggest an ancient, westerly wind path. These three populations of yardangs likely record three distinct wind regimes: a recent, Holocene path coming from the NW; an earlier, possibly glacial period, path originating due north and fanning out to the south; and a third, much older, westerly path, resulting from a different climatic or topographic setting. Our data reveal the utility of yardangs as paleoclimate indicators, and thus provides a framework to evaluate Quaternary atmospheric circulation.