Sedimentary Process And Its Environmental Significance In Southern Slope Of The Mariana Trench

Due to the “V” shape of geomorphology,the Mariana Trench,an eastward arc,becomes a sink of sediments,which has an impact on the biogeochemical cycle as well as the distribution and transportation of pollutants.In-suit observation and sampling process of Mariana Trench will cost a lot in both time and budget,so the sedimentary characteristics,composition,source of the Mariana Trench's research are still not well understood.In this paper,a sediment core of 2.25 meters was selected to explore the sediment composition and characteristics in the southern slope of the Mariana Trench by grain size analysis,biosilicon content analysis and SEM analysis.The effects of diatom size on the results of particle size analysis were studied.Based on the characteristics of diatom growth and sedimentary characteristics,the east Asian winter monsoon was extracted by grain grade-standard deviation.At last we discussed how the environmental factors effected the growth of diatom in different geological periods.The main composition of sediments is silt with poor sorting.The biosilicon's mean content is less than 2%.The size of the middle layer diatom shell is larger than that of the bottom layer.The mean grain size and sand content decrease significantly after removing the biosilicon.Grain size pretreatment method of sediment columnar samples on the southern slope of the Mariana Trench should be carried out by adding the experimental procedure of removing biosilicon.A large number of clay minerals and bioclasts are observed under scanning electron microscope.The clay minerals are mainly smectite and illite/smectite formation.The biological shell is damaged to different degrees.The content of diatoms is more than radiolarians and sponge bone needles.Sensitive grain size components,4.6-11.1 ?m(fine component)can indicate the evolution of east Asian winter monsoon(EAWM).Before the Holocene,the content of fine components is high in the periods of 19-16 cal ka BP(Haenrich 1)and 13-11 cal ka BP(Younger Dryas).The content of fine components is relatively low in 24-19 cal ka BP(H2-H1 warm period)and 16-13 cal ka BP(B/A warm period),indicating that EAWM was gradually weaken.At this time,lower nutrient content made diatom's shell size small.In the early Holocene period of 11.2 to 9.5 cal ka BP,EAWM was still in an enhanced state.Moreover,the content of fine components increased to different degrees,which corresponds to the period of higher nutrient and diatoms were in good growth with larger size.