南海北部初级生产力的物理-生物海洋学耦合特征及其对固碳量的影响

The physical-biological oceanography coupling characteristics of primary production in the northern South China Sea and the influences on carbon fixation

通过修订的VGPM模型,利用南海北部7年平均SeaWiFS和AVHRR遥感资料,分析了该海域河口上升流及反气旋涡等生境表层叶绿素浓度和初级生产力的周年变化,结果表明,季风驱动下的物理-生物海洋学耦合过程是控制研究海域浮游植物生物量和初级生产力时空变化的主导因素。浮游植物生物量和初级生产力随着季风、环流以及中尺度涡等物理现象的更替而呈现出明显的区域差异和季节变化,其高值一般出现在珠江口和沿岸上升流区,而低值则出现在外陆架反气旋涡和海域南端,往往伴随东北季风的盛行而升高,随西南季风的增强而降低。通过遥感资料估算得到南海北部海域年平均初级生产力为165.6 g/(m2.a)(以碳计),浮游植物年固碳量为4.83×107t/a(以碳计),其中每年最多约有1.9×107t碳向真光层外输出。

Based on an improved VGPM model and 7 years average data from SeaWiFS and AVHRR, the annual variation of surface chlorophyll a and primary production in different environments （e. g. estuary, upwelling and eddies） in the northern South China Sea （nSCS） was analyzed in this study. The results show that the physical-chemical-biological coupling processes driven by monsoon are the main factor controlling the spatial-temporal variation of phytoplankton biomass and primary production. With the changes of physical features （e. g. monsoon, circulation and eddies）, chlorophyll a and primary production show great variation. The high values appeared in the Peal River Estuary and coastal zone and the low ones appeared in the shelf anti-cyclonic eddies and the open sea. According to their temporal change, in most cases, the phytoplankton biomass and primary production are high when the northeast monsoon prevails and low when the southwest monsoon does. In general, the chlorophyll a and primary production in the study area decrease with water depth increasing from coastal area, continental area to open sea. In the coastal area with water depth lower than 50 meters, both chlorophyll a and primary production maintain at a high level, with chlorophyll a higher than 1 mg/m^3, and primary production higher than 600 mg/（m^2·d）. And the high chlorophyll a and primary production exhibit clumped distribution. In the coastal zone and inner continental shelf, chlorophyll a and primary production decrease rapidly with water depth increasing. However, the decrease gradually slows down in open sea. The lowest chlorophyll a and primary production appears on the most southern part of the study area. It is also observed that chlorophyll a and primary production show apparent seasonal changes, and the seasonal changes are different in different zones. In the coastal zone, the distribution of chlorophyll a shows a double peak curve, with higher values in winter and summer, but lower in spring and autumn. While, primary production only has single peak, which appears in winter. In the outer continental shelf and open sea, both chlorophyll a and primary production have the same seasonal change with only one peak in winter and trough in summer. In terms of the whole study area, the primary production is highest in winter [608 mg/（m^2· d）] and lowest in summer [-292 mg/（m^2· d）]. The primary production in spring[448 mg/（m^2· d）] is slightly higher than that in the autumn [399 mg/（m^2·d）]. And the average value is 437 mg/（m^2·d）. Finally, based on the remote sensing data, the annual carbon fixation in the nSCS was estimated （4.83×10^7 t/a）, and there are at most 1.9×10^7 t/a carbon exported the outside of the euphotic layer as new production.