Vertical Distribution And Controlling Factors Of Particulate Matter In The Northern South China Sea

The ubiquitous particulate matter in seawater are instrumental in the circulation process of many marine biogeochemistry processes.The formation and dissolution of particulate matter directly affects the chemical composition of seawater and the migration and transformation process of elements.It is of great significance to carry out research on seawater particulate matter.Here,single particle analysis is used to investigate the water-column particulate matter from A9 and SEATS stations in the northern South China Sea in May 2016.According to the topographical features and elemental compositions,the particles are classified into siliceous,calcareous,strontium sulfate biogenic particles and organic detritus,Si-Al containing,heavy metal containing,sulfur containing,salts and other particles.Siliceous biogenic particles,calcareous biogenic particles and organic detritus are main products of photosynthesis and incomplete degradation of siliceous and calcareous phytoplankton.Strontium sulfate biogenic particles are mainly derived from protozoa acantharia and their fragments.The Si-Al containing particles are mainly terrigenous quartz and various aluminosilicate minerals.The heavy metal containing particles are mainly related to human activities.The sulfur containing particles may come from aerosol and the crystallization process of seawater,salts and other particles may be the crystalline product of seawater remaining in the filter membrane.Si-Al containing particles,siliceous biogenic particles and calcareous biogenic particles are the main types of particulate matter in seawater,accounting for 37.9%,26.7%and 13.5%of the total number of particulate matters,respectively,and 78.1%totally.Their quantitative changes regulate the lateral and vertical variation of the total amount of particulate matter.In the upper 100m,the total amount of particulate matter is controlled by the growth of siliceous biogenic particles and calcareous biogenic particles.Below 500m,and the massive decomposition of calcareous biogenic particles reduces the total amount of particulate matter.There is a good coupling between the content of Si-A1 containing particles and the content of siliceous biogenic particles and calcareous biogenic particles.The closer to the shore,the greater the input of the terrigenous Si-Al containing particles,and correspondingly,the higher the content of siliceous biogenic particles and calcareous biogenic particles.The input of terrigenous Si-Al containing particles in spring is much higher than that in autumn.Correspondingly,the content of siliceous biogenic particles and calcareous biogenic particles in spring is much higher than that in autumn.The content of Si-Al containing particles in surface seawater is inversely related to the content of siliceous biogenic particles and calcareous biogenic particles,which means that Si-Al containing particles may be an important source of nutrient elements required for photosynthesis process of phytoplankton in surface seawater.In view of the elemental composition of siliceous biogenic particles and calcareous biogenic particles,we believe that Si-Al containing particles may provide Si and Ca supply necessary for phytoplankton photosynthesis.