WHAT THE FLUX? DUST PRODUCTION FROM ABRASION OF AEOLIAN SANDS MEASURED BY PI-SWERL

Recent studies have suggested that sand dunes can be important global dust sources, despite the fact that dune sand is typically well sorted and contains a low percentage of dust-sized material. A better understanding of dust fluxes from a wide variety of dunes is necessary in order to improve upon estimates of global dust emissions. We used the PI-SWERL (Portable in situ Wind Erosion Laboratory) to measure fluxes of particulate matter <10 micrometers (PM-10) from 11 different sands. Samples were coarse to fine ranging from quartz-rich to gypsum sand that varied in degree of sorting and grain shape. Several samples contained no sediment finer than sand and some samples were wet sieved to remove fines. To measure dust flux, sand was subjected to different shear velocities over 60 second intervals, as well as to a 20-minute test at a constant shear velocity above the threshold for sand movement. Gypsum sands were the most prolific dust emitters of our samples. Long tests revealed that quartz-rich sands containing fines had a decreasing dust flux over time as resident fines were winnowed during saltation. Long tests of clean sands resulted in dust fluxes that increased over time, indicating the generation of new dust by abrasion. The removal of iron oxide coatings during saltation has been previously shown to be a viable mechanism for dust production and is a likely culprit in many of our samples. However, samples that appear to lack coatings may be producing PM-10 from chipping of sand grains, and this is certainly more likely for gypsum grains. Our results are consistent with other studies, and allow more accurate estimates of dust production from dunes from a variety of wind speeds and sand grain characteristics.