夏季南海北部浮游植物对上升流与羽状流的响应

Summer phytoplankton responses to upwelling and river plume in northern South China Sea

文章建立了基于真实场驱动的三维物理—生态耦合模型,利用模型定量分析了夏季南海北部上升流和羽状流过程对浮游植物生物量空间分布的影响程度及作用机制。首先,利用2006—2008年卫星遥感数据及2006与2008年夏季观测数据对模型进行了验证,结果表明,模型能较好地再现夏季南海北部上升流和羽状流过程,较好地反映出浮游植物的空间分布特征。模拟分析结果显示,夏季南海北部浮游植物主要分布在50m等深线以内。琼州海峡东部海域和汕头海域浮游植物垂向分布较为均匀,上升流的贡献均达到90%以上,表层水平平流输送是浮游植物主要的汇,生物过程是浮游植物的源。珠江口和汕尾海域浮游植物存在表层和次表层两个高值区,羽状流贡献35%～40%,主要促进表层浮游植物生长,而上升流贡献60%～65%,主要促进中底层浮游植物的生长。粤西海域上升流对浮游植物的贡献占92%,主要促进中底层浮游植物生长,而表层浮游植物浓度极低。整体上,夏季南海北部上升流和羽状流主要是通过输送营养盐的方式影响浮游植物的生长。上升流对营养盐的输送作用是向岸方向的爬升输送和平行于等深线的沿岸流输送共同作用的结果。跃层的存在改变了营养盐的垂向输送过程,是导致上升流和羽状流过程对不同水层浮游植物贡献差异的关键因素之一。整体而言,夏季南海北部浮游植物空间分布差异是以上升流、羽状流主导,环流—营养盐—生物过程共同作用的结果。

A coupled physical-biological3D model was established,which is forced by realistic forcing,to quantify the effects and underlying mechanisms of upwelling and river plume on the spatial distribution of phytoplankton biomass during summer in the northern South China sea(NSCS).The model was validated by using cruise data of2006and2008and remote-sensing observations from2006to2008.The results suggest that the model satisfactorily captures the processes of coastal upwelling and river plume dynamics that determine phytoplankton distribution.Model results indicate that summer phytoplankton in the NSCS were mainly distributed within50m isobath.In Qiongdong and Shantou,phytoplankton distributed evenly.Upwelling processes accounted for up to90%of the biomass,and horizontal advection in the upper layer was the main sink,while biological processes were the main sources for the phytoplankton biomass.In the Pearl River and Shanwei,phytoplankton shows surface and subsurface maxima:the river plume contributed35%~40%(mainly to the upper layer)of the phytoplankton biomass,and upwelling contributed60%~65%(mainly to the middle and bottom layers).In Yuexi,the phytoplankton biomass was extremely low in the upper layer,and mainly distributed in the middle and bottom layers;in total,upwelling contributed92%of phytoplankton biomass.In the NSCS,both upwelling and river plume processes stimulated phytoplankton through nutrient supply.In the upwelling process,nutrient supply reflected the combination of along-and across-shore nutrient transports.The thermocline,which alters vertical nutrient transfer,is the key factor affecting the variable contributions of upwelling and river plume processes for phytoplankton in different layers.Overall,the spatial variation of summer phytoplankton is mainly driven by upwelling and river plume processes,and by the circulation-nutrient-biological coupling effect.