Dissolved Inorganic Carbon And Air-sea Carbon Lfuxes In The Mid-west Of The East China Sea

One of the world’s largest river Yangtze River input to the central and westernwaters of the East China Sea, where is an important area of interaction betweenmainland China and the East China Sea, so exploring the carbon cycle of this area issignificant for illustrating the prediction on regional climate change in China. Thesystemic research is seldomly involved dissolved inorganic carbon and sea-air CO₂fluxes in the central and western waters of the East China Sea on the current study.To the present, though there are some knowledge on the air-sea CO₂gasexchangecharacteristics in the East China Sea, the obtained sources and sinks intensity differenormously in different seasons and regions. The reason leading to the source/sinkstrength is also lack of deep understanding, therefore, exploring the variation ofdissolved inorganic carbon and air-sea flux of CO₂in this area possessesimportantscientific and practical value.The samples and data acquisition based on the investigation in the central andwestern East China Sea in June, November2010and the Yangtze River Estuary inMarch, August, November2010off the coast. The distribution of the dissolvedinorganic carbon, air-sea flux of carbon dioxide and its influenced factors wereexamined in this paper, and some new knowledge was acquired.（1）In the mid-west of the East China Sea:In June2010, the central and western East China Sea was affected by the Yangtzediluted water, Yellow Sea Coastal Current and the Kuroshio Branch Current, sohydrological conditions were very complex. The investigation area of the inorganiccarbon system was mainly affected by the dynamic factors and the growth andreproduction of phytoplankton, therefore the spatial distribution of surface waterpCO₂was very uneven, which ranged from106to543μatm. Because of the role ofavariety of water masses, pCO₂had no significant correlation withtemperature andsalinity on the whole; however, in the open waters where was affected by terrestrialinput littlely, chlorophyll a and pCO₂showed good negative correlation, whichmeaned that phytoplankton growth and reproduction had important implications onthe pCO₂of theinvestigation area. Yangtze River Estuary and Hangzhou Bay areasposessed significantly high pCO₂, as the source of atmospheric carbon dioxide where up to11.50mmol·m-2·d-1carbon was released into the atmosphere in limited scope;and a strong atmospheric carbon dioxide sink existed in the123oE¹25oE,30oN³2oN, absorbing atmospheric carbon dioxide up to-87.67mmol·m-2·d-1.Overall, the central and western East China Sea was the sink of carbon dioxideduring the investigation in June2010, where the area of carbon sink strength was3.24x1010gC·d-1,and theinvestigation sea could absorb atmospheric carbon dioxideto carbon amounted to3.24×104tons one day.In November2010, based on the temperature and salinity analysis, the investigationarea was mainly affected by the Kuroshio Branch Current; the good negativecorrelation between pCO₂and temperature, salinity meaned that the investigationarea in Novembercorresponded to single homogeneous nature of the ocean watermass properties. Air-sea CO₂flux of thestations in November were2.69mmol·m-2·d-1³3.66mmol·m-2·d-1. The grid method might contribute toavoiding the uneven spatial distribution of stations, so the mean air-sea CO₂flux ofgridmethod was14.35mmol·m-2·d-1. The amount of CO₂released per day was2.34×104tC d^-1,therefore the central and western East China Sea was strong source ofatmospheric CO₂in November.（2）In the Yangtze River EstuaryIn March, August, November2010,Yangtze River Estuary was affected by theYangtze River runoff, Subei coastal current and upwelling,so temperature, salinity,CO₂system parameters and pCO₂showed a significant difference in time and space.The investigation result showed that pCO₂had no significant correlation withtemperature, but there was good negative correlation between pCO₂and salinity.Because of Yangtze freshwater inputing, the mixing of salt and fresh water madesalinity gradually increased; however, the value of pCO₂decreased because of themixing with low pCO₂seawater, therfore the result showed negative correlation.Air-sea CO₂fluxmean values were17.44mmol·m-2·d-1、-1.69mmol·m-2·d-1、11.58mmol·m-2·d-1respectively in March, August, November2010. The entiresurvey area were the source of CO₂in March, November, and326tC,220tC wererespectively released into the atmosphere every day in March, November; YangtzeRiver estuary was the source of CO₂,while outside of Yangtze Estuary was the sinkof CO₂in August, on the while Changjiang River estuaryreflected the weak CO₂sinks, and the daily absorption of CO₂amounted to35.4tC. A three month dailyaverage result of Yangtze River Estuary showed that mean170tC were released tothe atmosphere, so it was further confirmed that salt and fresh water mixing zone ofthe Yangtze Estuary was the source of atmospheric carbon dioxide.