Seasonal Variations And Controlling Factors Of The Air-sea CO₂ Flux In The Yangtze Estuary And Adjacent Sea Area

Under the background of global climate change, gas exchange between the ocean and atmosphere fluxes, especially carbon dioxide flux monitoring, estimation, deep understanding of biogeochemical cycles and global climate change is of great significance. Shelf edge sea zones as an important land and sea interactions, especially in the Yangtze River estuary and its adjacent waters, complex physical, chemical and biological processes, the Yangtze River to carry a large number of land-based sources of fresh water and inorganic substances injected into the waters, and significantly affect the waters physical, chemical and biological processes, making the region a typical area of the global carbon cycle research.In this study, data acquisition and sample survey data based on the East China Sea and southern Yellow Sea from 2003 to 2008 12 cruises on historical data and in August 2015 the South Yellow Sea six sections of 47 stations. Respectively, the East China Sea and southern Yellow Sea between the years-seasonal variations in gas CO₂ flux and its influencing factors were analyzed, the South Yellow Sea waters also affect mechanisms CO₂ high value summer in Northern Coastal Current region were discussed, and get and understanding the following results:This paper analyzes the seasonal change characteristics of sea surface pCO₂ and air-sea CO₂ flux, and discusses the relationship among sea-air CO₂ transfer, sea surface temperature and salinity, based on the filed observation data in Yangtze estuary and adjacent sea area from 2003 to 2008. The result shows that sea surface pCO₂ and air-sea CO₂ have significant seasonal variations in the study sea area. In spring, Southern Yellow Sea, offshore area and the middle continental shelf of East China Sea, South East China Sea have atmospheric CO₂ convergence, due to rising sea surface temperature and strengthening biological role in spring. Their seasonal average air-sea flux is?-7.77±6.59?, ?-11.08±8.99?, ?-2.94±6.78? ?mmol · m-2 · d-1? respectively. In summer, Southern Yellow Sea shows as the CO₂ source ?2.99±6.09??mmol · m-2 · d-1?, which is associated with lower water upwelling. And offshore area and the middle continental shelf of East China sea ?-4.81±8.92? ?mmol·m-2 · d-1?, South East China Sea ?-0.75±12.14? ?mmol ·m-2 · d-1? have atmospheric CO₂ convergence, because Thermocline formed by fresh water input blocks the water mixing, coupled with enhancement of photosynthesis. In autumn, based on enhanced north wind increases water mixing, and CO₂-rich sea water upwelling increases sea surface pCO₂, the entire sea area show as the atmospheric CO₂ source. In summary, carbon convergence presents a weakening trend in spring, gradual increasing trend in autumn.According to August 2015 summer survey data:The summer is the Yellow Sea sea surface pCO₂ and FCo2 distribution and change, mainly due to the distribution of the Yellow water masses?North Jiangsu coastal waters?Yellow Sea Warm Water and the water mixed with Yangtze River Diluted Water and Yellow Sea Warm water. The sea Surface pCO₂ distribution in the range of 193.60-592.19?atm, showed a great deal of unevenness. Northern sea area within the Yellow water masses, due to the summer thermocline, so that the surface can't get enough of biological nutrient supplements with biological weakened, and satellite remote sensing data also show that in the region of chlorophyll a content generally lower than 2mg/m3. And the region temperature, salinity show the same distribution with pCO₂, indicating that the region chlorophyll a and water masses of the original property by regional seawater pCO₂ average 412.54?atm, FCO₂ averaged 1.0107 mmol · m-2 · d-1 atmospheric C02 weak source. Central coastal stream in Northern region as rich in C02 underlying water Chung presented pCO₂ high value area, pCO₂ average of 462.47?atm, high primary productivity in the region, which shows the underlying water upwelling and biological effects, the underlying water upwelling dominates, and the strong performance of air source region of C02, FCO₂ average value of 7.28 mmol · m-2 · d-1. In addition, seawater flooded the region in addition to the terrain lift effect, nearshore complex flow system is one of its driving force. Diluted water in the Yangtze River and the Yellow Sea warm current mixing zone shallow water, land runoff obvious, stronger trend, showing a high temperature, low salinity characteristics. Proper temperature and adequate nutrients biological effects dominate the surface pCO₂ reduce regional average 298.48?atm, presented as a sink of atmospheric CO₂ stronger, FCO₂ strength of-6.78 mmol · m-2 · d-1. Go over the entire area of the South Yellow Sea Air FCO₂ with an average of -3.58 mmol · m-2 · d-1,47 stations in FCO₂ with an average of 0.8799 mmol · m-2 · d-1, atmospheric CO₂ sinks. Southern Yellow Sea this summer with previous studies showed weak source contrast to the results, the main cause of this factor is different survey area range, high pCO₂ area inland sea-air exchange rate is smaller, and relatively high value area small and large low area. As well as by human activities affect atmospheric pCO₂ increased year after year-sea-air CO₂ partial pressure is reduced, even by the source to gradually shift sinks. This also shows that the sea shelf edge with atmospheric CO₂ concentration increases, there is a gradual trend from weak to weak source sinks change.