The Carbon Migration In The Changjiang Estuary And Adjacent Sea

Marginal seas play a significant role in the global carbon cycle. This researchfocused on the biogeochemistry of carbon in the Changjiang estuary and adjacent sea.The characteristic of carbon distribution in water and sediment was investigated, andair-sea interface CO2flux and carbon migration was estimated. From the aboveresearch, we can get the following conclusion:(1) The air-sea CO2flux in the study area varied greatly in different regionsand different time, but the carbon sink strength had a tendency to increasing insummer during last decade. The air-sea CO2exchange was mainly controlled bymixing of water masses, biological production, etc. The inorganic and organiccarbon in seawater varied obviously, and their vertical distribution is mainlyaffected by hydrodynamic. The apparently high DIC contents in the10m layernear the estuary may be a block of surface DIC migrating to the bottom whichmay lead to high pCO2in surface water of estuary.In summer2012, surface pCO2in the ECS ranged from96.28to577.7μatm(mean=297.6μatm). Low pCO2levels were found in the intersection area of theChangjiang Diluted Water(CDW)(123°-125°E,30°-33°N), whereas high pCO2levelsoccurred in the southern ECS shelf affected by the Taiwan Current Warm. Theaverage summer FCO2was-6.410±7.486mmol C·m-2·d-1, indicating that the ECSserved as a CO2sink which absorbed (1.83±1.98)×104tC every day during summer.The regional carbon fluxes sorted as CDW(Changjiang Diluted Water)>YEMW(Yellow Sea and East China Sea Mixing Water)>SMW(Shelf Mixing Water)>CUW(Coastal Upwelling Water)> TWCW(Taiwan Warm Current Water). Surface pCO2and FCO2was controlled by the Changjiang freshwater input and mixing, TaiwanWarm Current water and biological production. Comparing the historical data, theeffect of ECS as a CO2sink was gradually enhancing in the last ten years. This CDWenhancement FCO2was by-0.814mmolC·m-2·d-1every year, meaning that everysummer the CDW could take up5.46×104tC more than last year’s. The increased CO2sink in the CDW might be ascribed to the elevated Changjiang runoff in summer, andthe increasing of CO2sink may be temporary.In summer2013, the surface DIC and POC contents in the Changjiang estuaryand adjacent sea were higher than the summer of2012. The TA and DIC increasing may be attributed to Changjiang diluted water shortage and Yellow Sea Waterintrusion with high TA. The surface POC contents highly relevant with TSM weresignificantly affected by terrigenous input. As the diluted water eastward, the particlesgradually settled, therewith POC and TSM contents in seawater fell down. Theinorganic and organic carbon vertical distribution in the Changjiang estuary andadjacent sea was apparently influenced by water stratified in summer. The DICcontents near the estuary were enriched in10m layer. High concentration of10mDIC may have hindered the downward transport of surface DIC. And it may lead tohigh surface pCO2in estuary. However there is no apparently enrichment of DICappeared away from the estuary.(2) In summer the export flux of carbon from the Sea East China Sea to theJapan Sea was76.0tC/s, and the DIC accounted for96.06%, indicating that DICmigration was dominant in marine carbon cycle. The carbon input and output inthe East China Sea in summer was not balanced, which means carbontransformation may occurred in the sea water and there were some other carboninput ways. The Changjiang estuary had a great carbon deposition, and mostriverine PIC was trapped in the estuary zone.The major carbon input(DIC, DOC and POC) of the East China Sea was fromthe Taiwan warm current water, and the major output was into the Japan Sea, the netoutput carbon flux into the Japan Sea was76.0tC/s, in which DIC accounted for96.06%. Sedimentary burial is another big carbon output of the East China Sea, withthe shelf basin sediment flux of organic carbon being0.15tC/s. The carbon input andoutput in the East China Sea in summer was not balanced, which means carbontransformation may occurred in the sea water and some other carbon input ways wereneglected. The submarine groundwater discharge seeping into the Changjiang estuarycould give another DIC input flux range from0.142to0.708tC/s, and the addedcarbon input in East China Sea made a balance between the input and output.Deposition in the adjacent area in the Changjiang estuary had a significant effecton estuary carbon migration. The annual sediment trap flux of organic carbon in thestudy area accounted for about a third of the riverine flux of DOC and POC, and theannual sediment trap flux of inorganic carbon accounted for88%of the riverine PIC flux. The carbon flux from Changjiang estuary to East China Sea was0.88tC/s, inwhich DIC was the main output form and PIC was least.