Response of sediment magnetism to violent tropical cyclones (Typhoons) on the South China coast

Tropical cyclones (TCs) often affect the surface sediments of coastal areas, but the understanding of the redistribution of coastal materials resulting from TCs is far from adequate. Here, we present magnetic and grain size records from the seafloor sediments along the Leizhou Peninsula coast in the tropical South China before and after two violent TCs (Mangkhut, and Barijat) occurred in September 2018. Magnetic minerals mainly consist of magnetite and hematite. After the TCs subsided, the content of hematite increased compared to magnetite, which is reflected by the increased “hard” isothermal remanence and decreased S_-300. Meanwhile, magnetic minerals coarsened, as the decrease in the ratio of anhysteretic remanence and saturation-IRM. This is due to the preferential settlement of the newly formed hematite, and sediment sorting of the high-density minerals. The amount of fine clay (<2 μm) decreased, and coarse sand (500-2000 μm) increased, apparently after the TCs indicating stronger scouring than suspending. The combination of magnetic and grain size properties is useful to delineate the TC-induced sediment deposition, which probably provides convincing tools to aid in the detection of the paleo-TC activity in tropical coastal regions.