Aeolian erosion and sand transport over the Mejillones Pampa in the coastal Atacama Desert of northern Chile

The Mejillones Peninsula in the coastal Atacama Desert of northern Chile is a region in which ocean–atmosphere–land interactions are particularly strong, resulting in enhanced alongshore winds that erode the surface and transport sand particles to the sea. Because the aeolian particles in the laminated sediments at the bottom of Mejillones Bay record long-term changes in the intensity of prevailing southerly winds, it is fundamental to understand aeolian processes such as wind erosion and sand transport to improve paleoceanographic reconstructions. The aim of the present study is to characterize the wind erosion process over the flat geomorphology of the northern portion of the Mejillones Peninsula, the Mejillones Pampa, including the influence of wind erosion on the initial particle size distribution and the associated fractionation processes of the mineralogical composition of moving particles, through field measurements. In addition, we test the ability of an existing saltation model (MB95) to reproduce the variability of the erosion process during the field experiment. Soil samples from 17 locations on this flat surface contain significant amounts of highly erodible particles with diameters in the 200–300 µm and 100–150 µm size ranges. Aeolian particles collected in BSNE sand traps located at different heights near the surface, exhibit a bimodal size distribution similar to that of the erodible fraction of the soils; the abundance of the fine class increasing with height. Small stones that have a spatially variable distribution can locally reduce the intensity of wind erosion. The mineralogical composition of moving particles is similar to that of the soils, with quartz, feldspar and calcite as the most important minerals, followed by clay minerals, gypsum and amphibole. A value of u*t is calculated for each soil particle size class. Subsequently, the elementary contribution of each size class to the horizontal flux is calculated using White (1979)ʹs equation and the total flux is finally obtained by integration. The saltation model successfully reproduces the variability of the wind erosion process during the field experiment, but over-estimates the vertically integrated mass fluxes measured in situ by two orders of magnitude.