Response of seafloor sediment composition to a strong storm event in the inner-shelf of Heini Bay, China

Episodic floods and storm events have significantly impacted the marine sedimentary environment and hydrodynamic processes of inner shelf regions. The influence of a storm event on the coastal sedimentary environment depends on its trajectory and intensity, making it difficult to forecast the environmental impact. We analyzed the grain size distributions and time-series of settling particulate matter during Tropical Storm Muifa by collection of settling particulate samples and surface sediment samples before and after the storm from the inner-shelf of Heini Bay, China. We determined end-member components from shallow sediment core data and sediment trap data using end-member modeling with coupled cluster analysis. The results show that this storm event increased the mean grain size of seafloor sediment due to the addition of coarser particles, but did not increase the particle size range of settling particles. These findings are confirmed by the extremely leptokurtic distribution of particle size and the single-peak at 50-53 mu m, indicative of improved sorting and very positive skewing during the storm period. Furthermore, the storm carried these coarser particles into the bay, so there was a coarser sediment texture in the middle of the bay. In addition, we identified a common end-member component responding to this extreme weather event from the settling sediment particles during Tropical Storm Muifa and the nearby shallow sediment core samples. Our reconstruction of this historical extreme weather event indicated there were two sedimentary fragments that corresponded to two high-frequency periods of historical storm events. This indicates that storm events redistribute sediment in the seafloor and cause structural changes of grain size composition.