A first wind tunnel study on the aeolian sand transport of coral sands

Although wind-blown sand activity may be crucial for the landform and stability of coral islands in the ocean, the characteristics of coral sand movement remain largely unknown. This study is the first to quantify coral sand flux by wind tunnel measurement with various wind speeds using coral samples collected from an island and a sand cay from Yongle Atoll, Xisha Island in the South China Sea. The particle morphology, grain size, chemical and mineral composition, as well as threshold wind speed, transport rate, and transport flux profile of blowing coral sands, were investigated and compared to those of quartz sands from an inland desert. The basic features of coral sand movement, including an increase in threshold wind speed with grain size and density, an increase in total rate with wind speed, and an exponential decrease in transported sand concentration with height, have been determined. Cay sands with a grain size of about 1.24 mm behave similarly to coarse quartz sands, whereas island sands with a grain size of 0.49 mm perform similarly to medium and medium coarse quartz sands. Contrary to normal desert and beach sands, the decay trend of the flux profile of coarse coral sand increases with wind speed, just as it does for coarse desert sand. Due to their irregular morphology, coral sands are difficult to entrain by wind, with a threshold wind speed of about 11.64 m s- 1 for island sand and 16.98 m s- 1 for cay sand, which are much greater than the 4.32 m s-1 for fine and 12.67 m s-1 for coarse desert sands in the wind tunnel. The results can be incorporated into existing sand transportation models and used to evaluate the influence of aeolian processes on the landform of coral islands.