| Marginal seas play a key role in the transport of terrestrial materials to the open ocean.Due to the high primary production,the horizontal transports（lateral transports）of organic carbon（OC）in the marginal seas are significant for the global carbon cycle research.Generally,the lateral OC transports are estimated by box model and numerical simulation.The former one can obtain the total lateral OC transports which can help understand OC budget,but lacks the transport structure and temporal and spatial changes in the interior and boundary of the marginal seas.The latter one can solve those problems,but it is very difficult to simulate and validate the complex ecological processes in the marginal seas.Hence,it is still uncertain of calculating the lateral OC transports.In order to overcome the problems mentioned above,we did some works as follows:（1）Taking the East China Sea（ECS）as our study area,we proposed a method based on remote sensing and numerical simulation to estimate the lateral OC transports.Firstly,using remote sensing data from 2003 to 2012,the surface dissolved organic carbon（DOC）concentrations were obtained by the inversion algorithm based on the absorption coefficient of colored dissolved organic matter and chlorophyll concentration.The surface particulate organic carbon（POC）concentrations were obtained by the inversion algorithm based on the particulate attenuation coefficient.Three-dimensional distributions of DOC and POC concentrations were estimated further based on the empirical DOC and POC vertical profile models.Secondly,using the ROMS ocean model,the circulation system of the ECS was simulated to obtain the three-dimensional currents in the ECS.Finally,the lateral DOC（POC）transports were estimated based on the satellite-derived DOC（POC）concentrations and the simulated currents.Through the methods above,we revealed the lateral DOC and POC transport structure in the ECS.In terms of annual mean transport,there was a lateral OC transport feature of extending from south to north and from west to east in the ECS,but significant seasonal variation.The POC fluxes was about 10 times lower than that of DOC,which was due to10 times lower of POC concentration.The higher lateral DOC transports were found in the Yangtze Estuary,Fujian and Zhejiang coastal areas,Taiwan Strait and Kuroshio region,but in the Yangtze Estuary,Fujian and Zhejiang coastal areas and Taiwan Strait of higher lateral POC transports.There existed a northward OC transport zone extending from north of Taiwan to the Yangtze Estuary,as well as three distinct eastward OC transport channels appeared at 26°N―26.5°N,27°N―28°N,29°N―30°N,which had significant seasonal variation and the intensity decreased from south to north.We also revealed the lateral DOC and POC exchange volumes and channels across the ECS boudaries.There was a net lateral DOC export with-1.63 Tg C yr-1 in the ECS.The net DOC import from the Kuroshio was lower than that from the Taiwan Strait,but the exchange volume was much higher than that from the Taiwan Strait.Without considering the import of YR,there was a net lateral POC import with 0.72 Tg C yr-1 in the ECS.The net POC import from the Kuroshio was slightly lower than that from the Taiwan Strait,and the exchange volume was equivalent to that from the Taiwan Strait.Because the OC exchange was determined by the currents,the main net OC import channels across the ECS boundaries were located on the east side of the Taiwan Strait and 26°N―26.3°N of 200m isobath which was to the northeast of Taiwan.The main net export channel was located on the 100―200m isobath of the northern boundary.（2）We proposed a method to analyse DOC transports of the Yangtze River（YR）by Lagrange tracers.Firstly,Lagrange tracers were released every month and simulated for one year.We could obtain the patterns and discharge of YR from different month through the patterns of Lagrange tracers.Secondly,the DOC transports from YR into the shelf were estimated according to the relationship between the DOC flux and the water discharge.Through the methods above,the Yangtze River water were widely distributed in the Yellow Sea（YS）,ECS,South China Sea（SCS）,Japan Sea（JS）,and a few entering in the Northwest Pacific Ocean through the Kuroshio in the ECS with a significant seasonal variation after an annual period（360 days）.The Yangtze River water stayed largest in the SCS,followed in the YS and the ECS（less than 20%）.The Yangtze River water staying in the ECS were fewer inshore than that of offshore,and more in the north than that in the middle and south.According to the relationship between the DOC flux and the water discharge,the annual average DOC flux was 1.72 Tg C from the Yangtze River.After an annual period among the total resident DOC in the ECS,it accounted for about 63%in the north of the ECS and about 35%offshore.（3）We also proposed a method to analyse POC transports of YR by simulating suspended sediments（or total suspended matter,TSM）.We input TSM of YR into the physical simulation to analyse the TSM transports of YR,in order to get the POC transports from YR into the shelf.Through the methods above,the TSM flowing from Yangtze River spread widely in the YS and the inshore ECS throughout the year,and the bottom TSM concentrations were higher than that of the surface.In autumn and winter,the TSM flowing from the Yangtze River was widely distributed.Meanwhile,the highest TSM concentration was found in the Yangtze River Estuary and the Hangzhou Bay,and followed in the North Jiangsu Shoal,but almost no TSM in the ECS shelf.There also formed a narrow and long zone along the coast of Fujian and Zhejiang,parallel to the coastline and seabed topography.In spring and summer,the TSM flowing from the Yangtze River was confined in relatively tight regions,and higher TSM concentrations were only found in the Yangtze Estuary and the North Jiangsu Shoal.In addition,about 54%of the TSM imported from the Yangtze River entered the YS,about 21%entered the ECS,and most of the remaining entered the SCS.In general,this study estimated the lateral OC transports in the ECS by combining remote sensing with numerical simulation.Compared with the traditional box model method,the proposed method can not only obtain the transport fluxes across the boundaries of the marginal seas,but also the transport fluxes within the marginal seas,which is more conducive to understanding the transport structure within the marginal seas.In addition,although this study is aimed at the ECS,the method for estimating the lateral OC transport fluxes can be extended to other marginal seas in the world. |
