The Distribution And Sinking Characteristics Of Transparent Exopolymer Particles In The Eastern Indian Ocean

The concentration distributions and sinking dynamics of transparent exopolymer particles(TEP)have been systematically studied via the multivariate statistical methods and an empirical model based on the samples and datasets collected in the eastern Indian Ocean(EIO)from 2017 to 2019,which reveals that the coupling effects of physical,biological,and biogeochemical processes significantly affect the production and fate and sinking behavior of TEP.The distribution of TEP concentration in the study area shows no significant interannual variations,but significant spatial variations.The horizontal distribution shows a significant decrease from the coastal waters to the open ocean,and from the surface layer to the bottom layer.It is showed that TEP of different subregions are contributed by phytoplankton of different groups.Diatom and dinoflagellate are the major contributors to the enrichment of TEP of the coastal area,while TEP of equator ocean are mainly secreted by cyanobacteria and dinoflagellate.The correlation between TEP and chlorophyll-a(Chl a)is weak,but they obey a significant power function relationship.The variation of nutrient concentration is closely related to the change of phytoplankton biomass and the process of cell secretion,so it can also significantly affect the dynamic distribution of TEP pool.The sinking rates of TEP in the study area also show significant regional differences.Generally the high-productivity and the stratified regions with stable water columns are more conducive to the settlement of TEP,with the fastest sinking rate presenting near the depth of 75-100 m.Correspondingly,the presence of upwelling exerts a blocking effect on the TEP settlement.The analysis results of the empirical model of stratification show that the existence of pycnocline in the stratified zone significantly affects the settlement pattern of TEP.The diffusion-dominated sinking regime above the density thermocline and the buoyancy-dominated sinking regime below the density thermocline determine the unique sinking pattern of TEP in the stratified zone,which are broken in the upweling zone in which the sinking pattern of TEP is restrained by the prevailing of turbulence.The coupling effects of biological and physical processes further alter the physical and chemical characteristics of TEP.The empirical model formula shows that the change of TEP particle size represented by the fractal dimension can lead to the significant variation of TEP sinking rate.Phytoplankton with different groups,bacterial degradation and grazing of zooplankton potentially result in the alteration of chemical constituents and morphological characteristics of TEP.In general,the absolute value of TEP concentration is determined by the biomass of this region,in which the oligotrophic characteristic indirectly affects the production of TEP by limiting biological activities.As for the spatial and temporal distribution of TEP,the hydrology and physical processes tend to be more dominated.All of the above factors ultimately contribute to the unique distribution of TEP in the study field.The study can provide theoretical and data basis for the study of biogeochemical cycling of biotic material and organic carbon deposition in the EIO and the findings are potentially suggestive for the follow-up research of biogeochemical and physical processes in the EIO.