Distribution Characteristics Of Black Carbon And Organic Carbon In The Process Of Land-Ocean Interaction In The East China

In recent years,“climate change,global warming,glacier melting,sea level rise”such a series of environmental problems were widespread,the global carbon cycle had become one of the focus of scientific research.Black Carbon as a part of terrestrial organic carbon,it has also received great attention for its role in the global carbon cycle.It is generally believed that black carbon is a highly aromatic polymer produced in the incomplete combustion process of fossil fuels and biomass,which has relatively stable chemical characteristics and can exist in the environment for a long time.With the deepening of the understanding of carbon cycle,the horizontal migration of terrestrial organic carbon plays an important role in river and ocean ecosystems,therefore,it is of great significance to clarify its transport fluxes.The land-ocean interaction area in the East China has unique geographical,physical,chemical and biological characteristics.The Yellow Sea is a typical temperate continental shelf sea,the water mass change and current have obvious seasonal variation characteristics,The East China Sea has one of the widest continental shelves in the world.And the input of the Yangtze River has an important influence on the biogeochemical processes of its estuary and carbon sources and sinks in the East China Sea.Therefore,in this study,we collected water samples with monthly time resolution were collected at Datong Station of the Yangtze River from January 2018 to December 2019.In April 2021,surface water samples from 61sites in the East China area（the Yellow Sea and the East China Sea）,including 55surface water samples,38 middle water samples,and 54 bottom water samples,through the spring voyage“Comprehensive survey of Yangtze estuary and offshore land-sea interaction and its environmental effects”conducted by“Dong Fang Hong 3”.The organic carbon and black carbon concentrations in the water suspended particulate matters were analyzed by Thermal/Optical Carbon Analyzer via the TOR method,DOC were analyzed by the high temperature combustion（HTC）method used Shimadzu TOC-V Total Organic Carbon Analyzer.we discussed the variations and spatial distribution characteristics,estimated the fluxes of POC,PBC and DOC,discussed the influence of transport characteristics of carbon cycle in the East China Sea.The main research results were as follows:（1）In 2018,the Yangtze River discharge was 787 billion m³and sediment transport was 81 million tons.In 2019,it was 922.8 billion m³and 105 million tons.The concentrations of TSS,POC and PBC in water were basically the same in 2018 and2019.In terms of seasonal variations,the concentrations of TSS,POC and PBC in water were the highest in summer and the lowest in winter,and in spring and autumn were similar.Both POC and PBC were positively correlated with TSS,indicating that the variations of PBC and POC concentrations were affected by rainfall erosion and runoff input in the basin.In addition,due to the influenced of monsoon climate,the overall rainfall in the Yangtze River basin showed an obvious time pattern of“high in summer and low in winter”,which made the concentrations of organic carbon and black carbon in the Yangtze River basin showed obvious seasonal variations and dry flood season variations characteristics.The concentrations of DOC in 2018 was about 1.90 times of that in 2019 due to the dilution effect of discharge rather than erosion effect.And the concentrations of DOC were the highest in winter,the lowest in autumn,and in spring and summer were similar.（2）In 2018,the fluxes of POC,PBC and DOC at Datong Station of the Yangtze River were 1.05×10¹²g,2.05×10¹¹g and 1.22×10¹²g,respectively.In 2019,it was1.45×10¹²g,2.32×10¹¹g and 0.75×10¹²g,respectively.Due to the significant seasonal variations of discharge in the basin,the fluxes of POC,PBC and DOC peak in summer and trough in winter.According to the comparison of relevant data,POC and PBC were transported from Datong station to the estuary of the Yangtze River,accompanied by continuous erosion of discharge and the input of new organic matter,therefore,their fluxes into the sea showed a trend of continuous increase.The contributions of POC,PBC and DOC fluxes to the East China Sea were 21.43-23.86%,27.08-30.15%and 33.70%in 2018,and 29.59-32.95%,30.65-34.12%and 20.72%in2019,respectively.（3）The concentrations of TSS,POC and PBC in surface water of the East China area were lower than the bottom water,mainly due to the deposition and re-suspension of particulate matter in bottom water.TSS,POC and PBC all showed high concentrations near the Yangtze River estuary due to the typical terrestrial characteristics of the Turbidity Maximum Zone in the Yangtze River estuary.The concentrations of DOC in surface water was slightly higher than that in bottom water,which was mainly affected by biological activities.Specifically,the growth of phytoplankton became active in spring,and DOC generated during photosynthesis was released in surface water,while DOC generated during respiration and degradation was decomposed in bottom water.The migrated and diffused of TSS,POC and PBC were mainly influenced by the coastal current system and the Kuroshio Current.In surface water,TSS showed a trend of northward diffused,while POC and PBC showed a trend of northeast migrated due to the Kuroshio Current.The migrated of TSS,POC and PBC in middle water showed no obvious changes trend.In bottom water,there was a horizontal diffused trend.The migrated of DOC was mainly affected by coastal current system,temperature and salinity,and hydrodynamic environment conditions.The DOC concentrations was negatively correlated with salinity,so it was higher in low-salinity areas where affected by water masses and ocean currents.