Intersections between wind regimes, topography and sediment supply: Perspectives from aeolian landforms in Central Asia

Abstract

The widespread aeolian deposits of the Central Asian steppes and piedmonts offer potential to better understand the dynamics of the major Eurasian climate subsystems over Quaternary timescales. However, current assumptions linking climate processes with aeolian activity remain poorly substantiated and potentially problematic: emerging datasets suggest that loess accumulation rates, and the timing of peak dust flux along the Tien Shan piedmont, are highly variable between sites; the degree to which desert dunes reflect wind regimes and therefore provide records of climate circulation is unknown; and the presumed genetic link between the region's desert dunes and piedmont loess deposits remains hypothetical. These uncertainties raise questions as to the nature of the relationship between aeolian flux, deposition and (palaeo)climate.Here we investigate the relationship between wind regimes and the distribution, morphology and timing of two aeolian landform types (dunes and loess) in the topographically diverse Ili Basin of southeast Kazakhstan and western China. We establish late Holocene ages for three dune sites and one loess profile and infer that the location and morphology of these landforms can be used to test their genetic link with recent wind regimes. We assess the morphologic characteristics of linear dunes at four sites using a semi-automated mapping approach, and analyse the variability in dune orientations with respect to sand-shifting wind trajectories identified from meteorological reanalysis data for each site. The most frequently occurring wind direction appears to be responsible for sediment supply, while the strongest winds drive dune orientation. Wind orientations are strongly influenced by topography. Back trajectories incorporating dust transport and deposition potential to the loess site suggest both westerly and northerly delivery of fine-grained material to the piedmont, and that the most common source areas lie in regions where surface sediment contains a mixture of coarse and fine-grained material to facilitate entrainment into suspension.