Construction And Application Of Satellite Inversion Method For Particulate Carbon Stocks In The Yellow Sea

Particulate organic carbon(POC)and particulate inorganic carbon(PIC)are important parameters for studying ocean carbon cycle.The Yellow Sea is a typical marginal sea in the northwest Pacific Ocean with unique regional characteristics and carbon source and sink pattern.However,there are limited studies on the dynamics of POC and PIC,and the estimation of their stocks.Moreover,the spatial coverage of in-situ data is limited,while satellite data can provide information with higher spatial and temporal resolution to improve the shortage.In this research,satellited-derived the algorithm of surface POC and PIC and the estimation model of their stocks are constructed based on the in-situ data conducted in the Yellow Sea from 2017-2021.The spatial and temporal distribution patterns and inter-annual variation trends of POC,PIC and their stocks were verified in the Yellow Sea from 2003-2021.The algorithms were furtherly selected to explore the related processes of carbon cycle in four typical areas.The main conclusions are as follows:(1)The NDCI and CIPIC were the most suitable satellite inversion algorithms for the surface POC and PIC in the Yellow Sea,respectively.The surface POC and PIC are higher in the nearshore than in the offshore in the Yellow Sea with the highest value occurring in spring and winter,and the lowest value occurring in summer.The averaged POC was 164.67 mg m-3.The high POC appeared in the northern coastal area in the Yellow Sea.The POC basically reached the peak value in March in region Shandong Peninsula and Northern Jiangsu shoal.The low POC mainly appeared in the middle of the South Yellow Sea in summer,which was consistent with the range of the Yellow Sea cold water mass.The averaged PIC was 26.69 mg m-3,and the high value appeared in the northern Jiangsu shoal and the peripheral area of Shandong Peninsula.There was a very obvious tongue shaped high PIC area near the Yangtze River estuary,and the low PIC mainly appeared in the middle of the North South Yellow Sea.The spatial and seasonal patterns of surface POC and PIC in the Yellow Sea were related to of primary productivity,water exchange,sediment re-suspension and terrestrial input.(2)Satellite estimation method for POC and PIC stocks were established based on the relationship between surface POC and PIC and column stocks in the Yellow Sea.The results showed that the POC and PIC column stocks were higher in the nearshore than in the offshore in the Yellow Sea.The averaged column stocks of POC and PIC were 5385.33 mg m-3 and 1268.7 mg m-3,respectively.The averaged annual stocks of POC and PIC were 22.07 Tg C and 5.21 Tg C from 2003-2021,respectively,with decreasing trends.These trends were similar to the interannual trend of chlorophyll a,while it was as opposed to the interannual trend of SST.The decline may be due to lower levels of phytoplankton production,ocean current transport and acidification due to the global warming.(3)Four typical regions,north cold water mass(NCWM),south cold water mass(SCWM),Shandong Peninsula(SDP)and Jiangsu Shoal(JSS)were selected in order to study the surface POC,PIC and their stocks systematically in the Yellow Sea.The results showed that surface averaged POC presented similar variations:Spring>Winter>Fall>summer in region NCWM,SCWM and SDP.The surface POC fluctuated steadily in region JSS.The POC had high correlation with the Chl-a in all seasons.The column POC stock all showed decreasing trends in four typical regions from 2003-2021 with the descending order:SDP>JSS>NCWM>SCWM.The averaged surface PIC showed similar seasonal variation with the order Winter>Spring>Fall>Summer in regions NCWM,SCWM and SDP.The surface PIC in region JSS was at the highest during the whole year,showing double peak pattern occurring in spring and autumn,respectively.PIC was positively correlated with the MLD in spring and autumn,but negatively correlated with PAR,NPP and SST in region NCWM,SCWM and SDP.The POC in region JSS was negatively correlated with Chl-a in all seasons,but not strongly correlated with other environmental factors.From 2003-2021,the column PIC in four typical regions showed different variation,which showed an increasing trend in regions NC WM and JSS,while decreasing trends in regions SCWM and SDP.The range of PIC in the NCWM was obviously lower than that in the other three regions.The value of column PIC was followed the order JSS>SDP>NCWM>SCWM.