南海北部夏季叶绿素a分布规律及影响因素

Distribution of Chlorophyll-a and its influencing factors in the northern South China Sea in summer

采用2002—2016年6—9月Aqua/MODIS叶绿素a产品分析珠江冲淡水在南海北部生态效应的季节及年际变化特征。6月来自陆源的营养物质在西南季风作用下向河口以东陆架区输运,浮游植物增殖,叶绿素a含量增大;7月河口以东高浓度叶绿素a覆盖面积达到最大;8月在减弱的珠江径流和环境风场共同影响下,口门外海高浓度叶绿素a覆盖面积明显减小;9月北部陆架区处于东北季风影响之下,河口以西覆盖面积逐渐增大。通过线性回归分析可知,珠江径流量是口门外海高浓度叶绿素a覆盖面积的主要影响因素,且这种影响有一个月左右的滞后效应。显著大于(小于)多年平均的珠江径流量和环境风场等因素共同作用,导致2008(2004)年表现为高浓度叶绿素a覆盖面积的极大值(极小值)年份。叶绿素a在南海北部陆架区的时空变化特征主要受冲淡水过程影响,订正过的卫星叶绿素a产品可以用来讨论珠江冲淡水的季节及年际变化。

Summer(from June to September)time series of 15 years(2002-2016)of chlorophyll-a(Chl a)from the Moderate Resolution Imaging Spectroradiometer(MODIS)Aqua products were collected to discuss seasonal and interannual variability of ecological response of the Pearl River Plume in the Northern South China Sea(NSCS).In June,under the influence of southwest monsoon,nutrients from the Pearl River Delta were transported eastward to the shelf area,phytoplankton bloomed and Chla increased.The coverage area over the shelf in the NSCS reached the maximum in July,and decreased in August when the river discharge and wind reduced.In September when the northeasterly wind prevailed in the NSCS,the coverage area with high concentration of Chla(AHCHL)west of the estuary increased.Linear regression analysis suggested that the river discharge was the main reason for driving the AHCHL variability with a time lag of about one month.The combined effect of stronger(weaker)than the multi-year mean river discharge and wind resulted in extremely large(small)AHCHL in 2008(2004).Because the spatiotemporal variability of Chl a in the NSCS was mainly influenced by the Pearl River Plume,the quality controlled satellite Chl a products can be used to discuss the variability of the Pearl River Plume.