Distribution And Influence Factors Of Dissolved Carbohydrates In The Bohai Sea And The Yellow Sea

Serving as important energy, storage and structural substance including marineorganisms, carbohydrates are one of the largest identified components in dissolvedorganic carbon in the seawater, which play an important rule in the marine food webcycle and marine carbon cycle. The Bohai Sea and the Yellow Sea are in differentlatitudes, the oceanic general circulation, terrestrial inputs and ecological system aredifferent, therefore, studies on the space-time distributions, transformations andinfluence factors of dissolved carbohydrates in the Bohai Sea and the Yellow Sea willbe very helpful to realise the ocean organic carbon cycle in the China offshore. In thisdissertation, the Bohai Sea and the Yellow Sea were investigated during summer andautumn in the year of2011. The concetration, space-time distributions and influecingfactors of dissolved monosaccharides (MCHO), polysaccharides (PCHO) and totaldissolved carbohydrates (TCHO) were studied, and their contributions to disslovedorganic carbon (DOC) in the investigated areas were also discussed. The conclusionswere drawn as follows:(1) In the summer and autumn of2011, the concentration distributions of dissolvedcarbohydrates in the Bohai Sea and the Yellow Sea displayed a decreasing trend frominshore to offshore sites, and were higher in the north and lower in the south areas.From the data of two transects, carbohydrates concentration were found higher inupper layers than that in the middle and bottom layers, and were also higher insummer than that in autumn.(2) In summer, the concentration of MCHO and PCHO in the subsurface water ofthe Bohai Sea and the North Yellow Sea ranged from4.0to23.7μmol C/L and2.7to22.6μmol C/L, with averages of14.9and11.7μmol C/L, respectively. In the SouthYellow Sea, the concentrations of MCHO and PCHO varied from3.0to13.1μmol C/L and0.7to21.5μmol C/L, with averages of8.0and8.5μmol C/L, respectively.The high value areas were found near the Laizhou bay, Bohai bay, Yalu river andShandong peninsula, and the low value areas were found in the middle region of theBohai Sea and the North Yellow Sea. In autumn, the concentration of MCHO andPCHO in the subsurface water of the Bohai Sea and the North Yellow Sea rangedfrom0.3to16.6μmol C/L and1.2to50.7μmol C/L, with averages of5.1and9.4μmol C/L, respectively. In the South Yellow Sea, the concentrations of MCHO andPCHO varied from0.5to15.4μmol C/L and0.1to9.9μmol C/L, with averages of7.3and4.4μmol C/L, respectively. The results in autumn were obviously lower thanthat in summer, and low concentration value appeared in the middle of the SouthYellow Sea due to the influence of the Yellow Sea Warm Current.(3) In summer, the concentration of MCHO and PCHO in the sea-surfacemicrolayer of the Bohai Sea and the North Yellow Sea ranged from3.9to24.1μmolC/L and3.3to30.8μmol C/L, with averages of14.6and15.6μmol C/L, respectively.In the South Yellow Sea, the concentrations of MCHO and PCHO varied from3.6to38.6μmol C/L and1.3to29.3μmol C/L, with averages of11.6and14.1μmol C/L,respectively. The concentrations were well-distributed in the Bohai Sea and the NorthYellow Sea and no obvious high value were found. Comparing with the seasurfacewater, the distribution trends were some similar. In summer, the concentration ofMCHO and PCHO in the sub-surface water of the Bohai Sea and the North YellowSea ranged from0.5to57.2μmol C/L and1.1to64.5μmol C/L, with averages of8.5and12.2μmol C/L, respectively. In the South Yellow Sea, the concentrations ofMCHO and PCHO varied from1.9to14.2μmol C/L and0.7to11.8μmol C/L, withaverages of9.0and4.3μmol C/L, respectively. The enrichment factors of theinvestigatied areas in the two seasons illustrated that the concentrations in thesea-surface microlayer were in some extent amplified in the Bohai Sea and the YellowSea.(4) The vertical distributions of carbohydrates concentration were conductedthrough the H transect and B transect, which showed high values in the upper layerand low values in the middle and bottom layers as a whole. By the influence of thermocline in summer, the supplement of nutrient substance from the bottom waterwas blocked, and extremely low values were found in some stations along with theYellow Cold Water. In autumn, the water in investigated areas was mixed in someextent, and the carbohydrates concentration ranged in a small scope.(5)The seasonal variations of MCHO and PCHO in the subsurface and sea-surfacemicrolayer of the Bohai Sea and the Yellow Sea were investigated during summer andautumn in the year of2011. The concentrations of MCHO and PCHO in both the twolayers showed the similar seasonal variations, which exhibibed higher values insummer than that in autumn. The concentrations of MCHO and PCHO in thesea-surface microlayer were in some extent amplified in both summer and autumn.The enrichment factors were higher in autumn than that in summer, especially in theBohai Sea and the North Yellow Sea.