Temporal And Spatial Variations Of Primary Production And POC Export Efficiency In The South China Sea Observed Using BGC-Argo Floats

Using the observations of two BGC-Argo floats deployed in the South China Sea(SCS),this paper evaluate the performances of two primary production(PP)models(VGPM,CbPM)in the SCS,and explore the temporal and spatial variations of primary production and POC export efficiency.Firstly,this paper evaluate and obtain the best method to estimate primary production for BGC-Argo floats in the SCS.The VGPM-retrieved PP is 5.3%higher than the measured value in summer,56.8%lower than the measured value in autumn and winter,and the averaged error is 33.0%lower than the measured value.The CbPM-retrieved PP is 86.8%higher than the measured value in summer,9.4%lower than the measured value in autumn and winter,and the averaged error is 27.3%higher than the measured value.CbPM model is more suitable for BGC-Argo floats to calculate marine primary production.Then we analyze the relationships between PP and their impact factors:chlorophyll concentration and sea surface temperature show the greatest effects on the primary production,and the effect of photosynthetically is not that important.Then,the temporal and spatial variations of CbPM-retrieved primary production were analyzed.In the seasonal scales,the primary production in the North South China Sea is the highest in winter,followed by spring and autumn,and the lowest in summer;the primary production in the South China Sea basin is the highest in winter,followed by spring and summer,and the lowest in autumn.For regional changes,the seasonal vartiation of primary production in the North South China Sea was largely,and in winter it is obviously higher than that in the basin area,but in other seasons,their observations are similar.Among the different impact factors,strong wind and low water temperature strengthened the mixingin the upper ocean in winter,which bring more the nutrient to the surface layer,and the light intensity and water temperature were not very important factors.Finally,the vertical distributins of POC were estimated using floats.In the Northern SCS,the seasonal variation of POC was much stronger that the values in winter was much larger than in summer,also due to the stronger wind mixing in winter.However,in the South China Sea basin,the seasonal variation is almost constant.Then we explored the POC flux and export efficiency.The export efficiency and primary production show a significant negative correlation in the South China Sea,which may be related to the zooplankton grazing,DOC export,seasonal decoupling between primary production and POC Export.Compared with different export efficiency inversion models,it is found that the global scale models can not be well applied to the South China Sea.