Application Diatoms Interpretation Of The South China Sea Since The Late Quaternary Paleoenvironment

The South China Sea (SCS) is one of the largest marginal sea of the West Pacific Ocean, which plays an important role in the monsoon climate variation of the East Asia. Diatom is one of the dominant groups found in marine. The ecological distributions of diatoms are closely related to physical, chemical and hydrological properties of the water masses and controlled mainly by ocean circulation. The diatoms in sediments can provide lots of information on paleoceanographical environments and paleoclimate variations, which contain invaluable data for the global environmental changes and climatic processes.The present study is based on a quantitative analysis of diatom from 72 water samples and 71 surface sediments samples collected in the SCS, and integrated with grain size as well as other relevant information. This paper present the influence of the coastal currents in SCS and the intrusion of Kuroshio Current and Indian oceans warm water in the paleoenvironment, discussed the preservative mechanism of the diatom remains under the ocean environment. The results are shown as follows:The diatom species composition and cell density were investigated from water sample collected in summer of 2007 in South China Sea. In total,35 diatom species belonging to 28 genera were identified. The dominant planktonic diatoms in South China Sea were Thalassionema nitzschioides, Pseudo-nitzschia pseudodelitissima, Pseudo-nitzschia pungens, Melosira sulcata, Pleurosigma naviculaceum, Chaetoceros spp. etc. The species composition and cell abundance of phytonic diatoms were influenced by water temperature, salinity and nutrient etc.Diatom analysis of 71 surface sediments samples shows rich diversity of 256 species belonging to 56 genera. The dominant groups were:Chaetoceros messanensis, Coscinodiscus africanus, Coscinodiscus nodulifer, Cyclotella stylorum, Ethmodiscus rex, Hemidiscus cuneiformis, Melosira sulcata, Nitzschia marine, Roperia tesselata, Thalassionema nitzschioides, Thalassiosira excentrica and Thalassiothrix longissoma etc. The hot water species Coscinodiscus nodulifer was the dominant species in the surface sediment. A diatom genus-Rutilaria, was recorded for the first time in China. And 13 new recorded species were observed:Asterolampra grevillei, Biddulphia turrigera, Cocconeis citronella, Cocconeis ocellata, Cocconeis cyclophora, Dictyoneis marginata, Entogonia davyana, Nitzschia campechiana, Plagiogramma Kinkeri, Plagiogramma Papille, Rutilaria radiate, Triceratium castelliferum, Triceratium contumax. The distribution pattern of diatoms reflected the difference of environmental conditions. The concentration of diatom in surface sediments varied between 71 and 623,438 valves pergram of dry sediment, the abundances of diatom frustule increased sharply from littoral to deep sea basin area. Diatoms distribution in surface sediments was influenced by submarine geomorphology, hydrodynamics and hydroclimate etc.Seven diatom assemblages were distinguished and the distribution of these assemblages is correlated with oceanic current patterns in the region. Assemblageâ… : Melosira sulcata-Coscinodiscus nodulifer-Pyxidicula weyprechtii-Diploneis spp.;â…¡: Cyclotella stylorum-Melosira sulcata-Coscinodiscus nodulifer;â…¢:Coscinodiscus nodulifer-Thalassiothrix longissoma-Roperia tesselata;â…£:Coscinodiscus nodulifer-Roperia tesselata-Thalassiothrix longissoma;â…¤:Coscinodiscus nodulifer-Thalassiosira excentrica-Roperia tesselata;â…¥:Coscinodiscus nodulifer-Melosira sulcata-Cyclotella stylorum;â…¦:Coscinodiscus nodulifer-Trachyneis antillarum-Hemidiscus cuneiformis. These assemblages may be of great importance for future palaeoceanographic studies.After dissolution, transfer, sediment and resediments, The diatom from sediments can reflect the composition of plantonic diatom groups partially.In paleoceanographic reconstruction of the area, Coscinodiscus nodulifer, Coscinodiscus africanus, Nitzshia marina, Hemidiscus cuneiformis may be used as indicators of the warm Pacific Ocean water, perhaps including the Kuroshio Current flowing into the SCS. Whereas Cyclotella striata, Cyclotella stylorum, Diploneis bombus, Diploneis crabro, Melosira sulcata, Trachyneis antillarum could be used to identify the influence of the coastal currents in SCS. And the occurrences of Thalassiothrix longissoma might be used as a signal of high primary productivity conditions.