The Interannual Variation And Influence Factors Of The Yellow Sea Cold Water Mass And Seasonal Acidification In The Yellow Sea

The Yellow Sea Cold Water Mass(YSCWM)is one of the most physical phenomena in the Yellow Sea.It can influence physical,chemical,and biological processes in the Yellow Sea.And in recent years,seasonal acidification which will impact ecosystem seriously in the Yellow Sea attracted extensive concern.We used a ROMS-CoSINE coupling model to simulate physical,chemical,and biological processes in the Yellow Sea from 1995 to 2008 and studied the interannual variation and influence factors of the YSCWM and seasonal acidification in the Yellow Sea.In this paper,the Empirical Orthogonal Function(EOF)was used to study the interannual variation of the YSCWM.The results showed that the temperature of the YSCWM had a weak rising trend,but the rising trend in the core region was less than other regions.There were two periodic signals in the temperature variation of the YSCWM.The stronger one was about 2 years and the weaker one was about 4 years.Then we studied the influence factors of the YSCWM.We found that the YSCWM consisted of the cold water locally formed in winter and the temperature in February had an important influence on the temperature of the YSCWM in summer.The temperature of the Yellow Sea in February was affected by the local wind speed and the air temperature but not by the Yellow Sea Warm Current.Meanwhile,the temperature of PN Section which is perpendicular to the axis of the Kuroshio in the East China Sea in winter half year would also influence the temperature of the YSCWM.In summer,there was a weak positive correlation between wind speed and temperature of the YSCWM,however,the temperature of the YSCWM did not correlated with the sea surface temperature.There was also a significant interannual variation,without evident variation period,of the seasonal acidification in the Yellow Sea.Both the interannual variation and the acidification mechanism in the Northern Yellow Sea(NYS)were different from those in the Southern Yellow Sea(SYS).The degree of the seasonal acidification in the NYS was larger than that in the SYS and the interannual variation in the NYS was also more significant than that in the SYS.In the NYS,the gradient of seasonal thermocline,especially the average from May to July,was the primary factor in the seasonal acidification.However,in the SYS,the average plankton biomass in the sea surface from spring to summer had a significant positive correlation with the seasonal acidification.In winter,the pH in the Yellow Sea had no connection with the water temperature.The results of sensitivity experiments about runoff showed that the NYS and the SYS were affected with various degrees.In the NYS,the decreasing river runoff would result in the decreasing temperature of YSCWM,the lowering the sea surface temperature,the obviously rising the sea surface salinity and the weakly intensifying the vertical stratification.In the SYS,with the river runoff decreasing,the decreasing trend of the temperature of YSCWM was not significant but the decreasing trend of vertical stratification was significant.Meanwhile,the variations of sea surface temperature and sea surface salinity were larger than those in the NYS.So the influence of river runoff on the the NYS was greater than that in the SYS in the deep layer.On the contrary,the influence of river runoff on the NYS was weaker than that in the SYS in the surface layer.The variation of pH suggested that the river runoff did not have a great influence on the seasonal acidification in the NYS but there was a significant positive correlation between the river runoff and the seasonal acidification in the SYS.And the results of the experiments on Changjiang River and Yalu River's influence area suggested that Changjiang River influenced the SYS mostly and Yalu River influenced the shallow water area of the NYS.Lastly,we compared the results of real topography and smooth topography to study the influence of the topography.The results showed that the real topography would lead to a lower temperature of YSCWM and stronger intensity of vertical stratification in the NYS but in the SYS,the difference was not obvious.However,both in the NYS and the SYS,the real topography would weaken the seasonal acidification.