Differences in sedimentary dynamic processes between summer typhoons and winter cold waves on the inner shelf of the East China Sea: Insights from in-situ observations

One of the major challenges addressing human life safety in the context of global warming is how typhoon activity may develop in the future. Our understanding of typhoon long-term development and evolution mechanisms is limited by the duration of instrumental recording. Extraction of typhoon information from sedimentary records in the muddy area of the East China Sea inner shelf is an effective method for understanding the evolution patterns of typhoons that have impacted China over the past thousands of years. The precision of typhoon event detection, however, might be affected by other extreme events, such as winter cold waves. One of the difficulties in reconstructing typhoon activity is to identify typhoon and winter cold wave deposition events. Using a quadripod observation system placed in the muddy area of the East China Sea inner shelf, seawater temperature, salinity, suspended sediment concentration, and currents during Typhoon Goni and winter cold waves were measured, and the differences in sedimentary dynamic processes between typhoons and winter cold waves were then discussed by combining wind speed, wind direction, and wave data from offshore observation buoys. Observations on typhoons and winter cold waves showed certain similarities in the changes in wind direction, significant wave height, and near-bottom current velocity, but typhoons′ higher strength made it easier to resuspend seabed sediments. Typhoon-related high suspended sediment concentrations are mostly caused by the resuspension of seabed sediments, whereas high suspended sediment concentrations during winter cold waves are primarily caused by Yangtze River discharge. Sand layers in the sedimentary record of the seaward side edge of the inner shelf muddy area in the East China Sea are likely to represent typhoon event deposition because of the difference in the direction of the near-bottom current between typhoons and winter cold waves. Therefore, event deposition layers are good research materials for studying the variation patterns of typhoon activity. The findings of this study can be used as a scientific reference for extracting more accurate typhoon information from sedimentary records of the muddy area in the East China Sea.