The Study Of Phytoplankton Sinking Rate In The Eastern Indian Ocean

Although eastern Indian Ocean(EIO)is the important part of global carbon cycling,but relative researches about carbon sink are scarce in this area.Thus,in order to investigate sinking rates of phytoplankton and carbon sink,two research cruises were conducted in Bay of Bengal(BOB)during autumn of 2016 and in EIO during spring of 2017,respectively.First,the phytoplankton community structures in the EIO were analyzed by Utermohl method.The results showed that Trichodesmium thiebautii was dominate species.Second,the SETCOL method was used to study the sinking rates of phytoplankton in EIO,calculate the sinking rate of dominant species of phytoplankton,and estimate the carbon flux of phytoplankton.The results showed that:(1)the sinking rates of BOB in the spring of 2016 were-0.11-3.95 m d-1,with an average of 0.84 m d-1.The sinking rates of EIO in 2017 were-0.29-2.19 m d-1,with an average of 0.43 m d-1,Correlation analysis showed that the sinking rates of phytoplankton was negatively correlated with temperature and positively correlated with other environmental factors,such as Phosphate,nitrate,silicate,depth.(2)The carbon biomass of BOB in 2016 ranged from 0.004 to 8.102 ?g C L-1,with an average of 0.581 ?g C L-1.In 2017,the carbon biomass ranged from 0.002 to 18.447 ?g C L-1,with an average of 1.534 ?g C L-1.The variation trend of carbon biomass in the two voyages was consistent,and it gradually decreased with the increase of depth.(3)In 2016,the carbon fluxes of phytoplankton ranged from-4233.34 to 14867.78 ?g C m-2d-1,with an average of 913.76 5.76 ?g C m-2d-1.In 2017,phytoplankton carbon flux ranged from-3124.71 to 6246.21 ?g C m-2d-1,with an average of 1118.43 ?g C m-2d-1.In the autumn of 2016,the carbon flux decreased with the increase of depth.In the spring of 2017,the carbon flux of phytoplankton in the eastern equatorial Indian Ocean followed the order:the layer of DCM>the layer of middle>the layer of last>the layer of surface.According to the result of cluster analysis and geographic distribution,the survey area were divided into five regions.the results showed that the phytoplankton sinking rates of coastal were higher than those of the open ocean,and the differentiation of carbon biomass and carbon flux between five regions were not obvious.In a word,because of various sampling time and site,the phytoplankton sinking rates in 2016 was higher than those in 2017,but the carbon biomass and carbon flux of phytoplankton were lower than those in 2017.Above all,in this area,carbon fluxes of phytoplankton exhibited obvious spatio-temporal heterogeneity and were affected by multiple factors,such as phytoplankton community structure,Marine physical and chemistry environment factors and so on.In this study,the distribution patterns of carbon sink of phytoplankton in EIO are clearly descripted,which lay a foundation for the future research on the carbon cycle process in EIO.