Researches On Coastal Storm Surge Frequency During The Warm Period Of Middle Holocene In Middle Jiangsu Province

The possible influence of the global warming to storm surge frequency has been one of the concerned questions at present for researchers. Some of them consider that the frequency will increase according to the results of observation and simulation, but some others don't agree to it. To verify the speculated conclusions, the coastal storm surge frequency in middle Jiangsu province during the warm period ofmiddle Holocene is discussed in this thesis.To make clear the mechanism of silt-mud couplets in tidal flat, the flat of Dongtai, Jiangsu province is selected as a typical place for researching. Materials deposited in 8 sites in this place were collected continuously during half a month, and sediments in these sites were also sampled several times in a year. Field observation and lab experiments prove that the tidal sediments show both of daily and half-monthly periods. In a half-month cycle, the couplet's thickness varied regularly from thinner to thicker, which corresponds to neap tide-spring tide.The field observation of the sediments of storm surge produced by No. 11 typhoon in 1997 shows that sedimentation rate of storm surge sediments are greater than that of normal astronomical tide sediments, and the grain size shows relative coarse with poor sorting. Vertical sequences of the storm sediment show parallel bedding and overlapped by hummock bedding. These characteristics provide good basis for building the index of storm surge deposit. In this field observation we also find an important fact that, even during storm surge period, high tidal flat can still be in sedimentation in some place, no erosion occurred.To tell the typhoon storm surges from cold wave storm surges, 12 monthly sedimentary samples are collected from the modern tidal flat surface at Dafeng, Jiangsu. Palynological analysis of these samples indicates that the seasonal palynological features of the tidal flat sediment are very obvious and some palynological indexes, such as taxonpercentage of Arboreal, Herbaceous pollen and spore, are good indicators to tell the seasonality of the tidal flat deposits. A sedimentary sequence formed between 1984-1994 is used to check this method. Checking result suggests that this method is acceptable and the Taxon percentage of Arboreal pollen is the best indicator for the seasonality of tidal flat deposits.Three column sections have been collected from Shanggang, Yancheng to analysis the storm surge frequency during the warm stage in middle Holocene. The results of lithology, dating age by 14C, foraminifera assemblages, calcareous nannofossils and palynological features indicate that the deposits were tidal flat deposits formed in the warm period of middle Holocene. The researches of the rhythmites of thicker silt layers and the characteristics of storm deposits show that the storm surge frequency is once every 2-4 years, yet modern storm surge with equivalent intensity occurs one time every 12 years. So the storm surge frequency in the warm period in middle Holocene is higher than that of today and we can speculate that the frequency will increase with global warming.