| Human beings are suffering a lot of environmental incidents including global warming, sea-level rising and ecosystemdeteriorating under the situation of global change. Sea-level rising caused by global warming influences the people live in coastal areas a lot and some researchers predict that some low-altitude islands located in Pacific will be submerged by the sea-level. On the other hand, sea-level rising will also impact the shipping, watersupplement and urban drainage system. The study on sea-level is theoretically meaningful and important in reality application.The sea-level change in Holocene recorded by geological evidence has a close relationship with the migration of human beings. Through studying sea-level change in Holocene, we can get a general idea of the change pattern of sea-level. Some materials and methods such as basal peat, cheniers, microfossils and coastal notches are widely use in reconstructing the sea-level curve of Holocene. However, these qualitative methods which based on lithology and14C is not as accurate as the quantitativemathematic model such as transfer function.Marine microfossil transfer function is a new technique and develop with the thrown of computer science.This method combines statistics and mathematic model and indicates the relationship between modern samples and their environmental variables by transfer function. Then the transfer function will be applied to the sediment core to reconstruct the geographic information of the past. Nowadays the transfer function has already become an indispensable method in the study of sea-level in the western countries. But such research achievement is very limit in the coastal areas in China. This paper intends to introduce the method of the diatom (collected at two tidal flats in Chongming island) based sea-level transfer functions, including tidal flat sampling strategy, statistical analysis and possible prediction errors and its feasibility of the application in Yangtze river mouth. After analyzing the surface samples of two profiles (SY and BBG) collected from at two tidal flat in Chongmingisland, we find that the diatom species is distributed according to vertical zone. And the following CCA ordination analysis showed that the SWLI (represent the elevation variable) is the most contributing factor among all the environmental variables. Thus, the transfer functions of SY were made with weighted averaging (WA) and weighted averaging partial least squares (WA-PLS).The correlation (R2_jack) is0.9and the RMSEP is12.6with all samples of transect SY. The precision may be improved to±10cm when the sample from supratidal site (sample of SY1) is excluded. On the other hand, we developed the transfer function of BBG with partial least square (PLS) and WA-PLS. The component2of WA-PLS provided the highest Jack_R2(0.91705) and smallest RMSEP (7.6553). However, the component2of PLS performed better than it because the relationship between diatom species and elevation accord more with unimodal model.Through the study in the paper, we can basically draw3conclusions as follows. First, the distribution mode of tidal surface diatom species of northern coast of Chongming island is obviously vertical and the dominant diatom species of each zone was totally different. Secondly, the surface samples of tidal flat werecontrolled by the environmental variables such as salinity and pH of porewater, elevation, TOC and grain size. Thirdly, the diatom base transfer function for SWLI of two profile (SY and BBG) perform both satisfactory with high correlation (Jack_R2) and low RMSEP. These results will give us a message that the diatom based transfer function for sea-level reconstruction is feasible in this area.The study on surface tidal diatom species and their correlated environmental variables is very rare. In this paper, the modern surface tidal samples were almost located at the middle and high marsh. So our database of the surface samples should be improved further. The transfer function developed in this paper still cannot be applied to the sediment core to reconstruct the sea-level fluctuation because of the incomplete modern database. But we expect this research will push such quantitative methods forward to a higher level in high resolution sea-level reconstructions that can help produce high quality geological records to aid coastal management of China. |
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