Analysis Of Temporal And Spatial Characteristics Of Sea Surface Chlorophyll-a Concentrations In Northern South China Sea Based On Long-time Series Remote Sensing Data And EOF Method

The chlorophyll-a concentrations was considered as one of the most importantindicators of eutrophication in marine ecosystems, its spatial and temporal variationscan reflect the effect of marine biogeochemistry well. So the research of spatial andtemporal variations of sea surface chlorophyll-a may play an important role inmonitoring marine environment and revealing the marine ecosystems dynamicchange.This research collected long time series remote sensing sea surface chlorophyll-aproduct in Northern South China Sea from2002to2012. Firstly, the monthlyaveraged sea surface chlorophyll-a concentrations images were statistically analyzed,and the research area was divided into two part, the area from30to200meterisobaths and the area deeper than200meter isobaths, respectively. Then empiricalorthogonal function （EOF） decomposition was carried out to the monthly averagedsea surface chlorophyll-a concentrations images of those two areas. The statistics anddecomposition result were used to analyze the spatial and temporal variations of seasurface chlorophyll-a concentrations. Finally, the same time series of Sea SurfaceTemperature （SST） data was collected to discuss the relationship betweenchlorophyll-a concentrations. The results are as follows:On spatial distribution: firstly, the concentrations of coastal area are higher thanthose of open sea area, and the far from the shore the rapidly the downward trend willbe. The maximum of concentrations almost appeared in the coastal area of mainlandof China. Secondly, the sea surface chlorophyll-a concentrations are almost below1mg·m^-3in the area deeper than30meter isobaths. Thirdly, the overall variations ofconcentrations in the area from30to200meter isobaths are not obvious, except theeast coastal area and the west coastal area. Fourthly, the whole variances ofconcentrations in the area deeper than200meter isobaths are not notable, except thearea near the Dongsha Islands and the area on the north-westward side of LuzonIsland.On temporal change: firstly, the seasonal distribution varied in differentchlorophyll-a concentrations. The concentrations bigger than1mg·m^-3were relatively stable. However, the seasonal distribution of the concentrations from0to0.1mg·m^-3and from0.1to1mg·m^-3were notable and turned on opposite trend. The areapercentage of chlorophyll-a concentrations from0to0.1mg·m^-3were: fromDecember to June, the area percentage increased first and then decreased with thepeak value occurred in May. Generally, the area percentage was low in winter andalmost lower than2%. From the July to November, the trend rised first and thendeclined with the peak value appeared in August. Secondly, the seasonal variation ofchlorophyll-a concentrations was obvious and the seasonal pattern varied withdifferent part of the sea. Namely, in the northern coastal area, the highest values weremainly in summer, while the lowest values occurred in spring. In the western coastalarea, the peaks happened in autumn or winter and the trough in summer every year. Inthe large area north-westward side of Luzon Island, the maxima took placed in winterwith minima showed in summer or autumn. In the area near Dongsha Islands, thecrest of value was found in winter year by year.According to the correlative analysis between sea surface chlorophyll-aconcentrations and SST, there was relatively high connection between them within thearea deeper than200meter isobaths in Northern South China Sea.