Field observations of dust transport rates in Gobi deserts

摘要

Abstract Gobi deserts are a major dust source in northwestern China, but emission and transport of dust and coarser materials from these deserts are not fully understood. We measured sediment transport in a Gobi desert in northwestern China in 2015 and during a strong dust storm on 4 April 2018. We integrated field measurements with high-resolution laboratory sediment analyses to explore dust emission, transport above the Gobi desert, and the role of upwind sediment deposits on dust emission and transport. Sediment transport was greater at sites with rich upwind sediment deposits than at sites with less available upwind sediment. Sediment transport and the particle-size distribution showed high spatial heterogeneity and were controlled by sediment availability. The ratio of the sediment grain sizes at 25 and 100 cm above the surface to the sizes of sediment collected at the surface (f25 and f100, respectively) and the proportion of the measured transport rate (gm) at a given height explained the effect of upwind sediment availability on sediment transport. The spatial heterogeneity of f25, f100, and gm were reasonable indexes to explain the sediment sources and differences of sediment transport above the Gobi desert. The depletion (f25 and f100  125 μm), transit (both f25 and f100  1) of very fine sand (63–125 μm), and enrichment (f25 and f100 > 1) of clay and silt mean that clay and silt were transported from a distant sediment source rather than emitted from the local Gobi desert.