Carbon Sink Phytoplankton In Bohai And Yellow Sea

Currently,Ocean carbon sink is the frontier and hot area of international scientific research.The carbon sink function of China sea has not been clearly determined and quantified.Through field observation,field experiment and laboratory simulation,the contribution of three biological carbon sink pathways related to phytoplankton was explored.Sedimentation of phytoplankton in Bohai and Yellow Sea was studied during three cruises carried out in the summer of 2016,autumn of 2017 and spring of 2018.In addition,there is no comprehensive study in this area during the spring,therefore phytoplankton community in spring 2018 was investigated,and transparent exopolymer particle(TEP)was researched at the same times.This paper will provide some data to support and reference for the study of carbon cycle in survey area.Phytoplankton community was studied by using Utermohl method.In spring,phytoplankton community was mainly composed of diatoms and dinoflagellates with diatoms being more dinoflagellates.The predominant species were Paralia sulcata,Thalassiosira sp.,Thalassiosira pacifica,Chaetoceros spp.,Asterionellopsis glacialis and Leptocylindrus danicus etc.Some diatoms and dinoflagellates have significant correlation with phosphate,but the correlation coefficient is not high.Spatially,phytoplankton cell abundance in spring was mainly distributed in bohai strait and area beyond the Yangtze River estuary.Vertically,diatoms were mainly distributed in the subsurface layer,and dinoflagellates were in the surface layer.Inshore index about Shannon-wiener diversity and Pielou uniformity was higher than the ocean.SETCOL method was used as the standard method to research phytoplankton sinking rates,in the meanwhile,phytoplankton carbon sedimentation was reckoned.It was found that the sinking rates in early autumn 2017 was higher than that in spring 2018 and summer 2016.On the whole,the bottom layer had the highest sinking rates,followed by the middle layer and the surface layer.Correlation analysis showed that the sinking rates were significantly correlated with salinity,silicate and nitrate.In terms of phytoplankton carbon sedimentation flux,its average value was 5.17±0.84 mgC m-2 d-1 in Bohai and Yellow sea.Bohai sea had the highest carbon sedimentation flux,followed by the north Yellow sea and the south Yellow seaThe concentration of Transparent exopolymer particles was measured,and the sinking rate was also measured.Meanwhile we were estimated for carbon sedimentation flux.The concentration of TEP ranged from 32.5 to 817.7 ?g Xeq L-1,which was significantly correlated with the concentration of the chlorophyll a.In vertical distribution,the Bohai sea was relatively uniform,the north Yellow sea was mainly distributed in the upper water,while the south Yellow sea was mainly distributed in the lower water.The sinking rate of TEP was 0.38?1.75 m/d,and the south Yellow sea had the highest sinking rate,followed by the Bohai and the north Yellow sea.The carbon flux of the TEP was-24.22?411.07 mg C m-2d-1,with an average value of 43.80 mg C m-2d-1,it was signi ficantly higher than the carbon flux of phytoplanktonIn the middle of Yellow sea,the fecal abundance ranged from 0.64 to 3.51 mg C m-3,the main component was faeces below 200 ?m.The carbon flux of zooplankton faeces was 0.036?0.14 mg C m-2d-1 in the middle of the Yellow sea.These studies indicated that the sinking of phytoplankton and TEP was all vital pathway for carbon sedimentation in Bohai and Yellow sea,which provides an important basis for the carbon sinking in Bohai and Yellow sea.