南沙渚碧礁生态系有机碳的分布及周日变化特征

Distribution and Diurnal Changes of Organic Carbon in Zhubi Reef Ecosystem, Nansha Islands

1999年4月对我围南沙群岛渚碧礁海水中溶解有机碳的分布及礁坪区颗粒有机碳(POC)和溶解有机碳(DOC)的周日变化特征进行了观测。结果表明．渚碧礁表层海水DOC变化范围为1．43～3．62mg/L，平均为2．16mg／L，含量分布大致表现为礁坪区>渴湖>礁外。渴湖DOC的垂直分布大致表现为表层高于底层，可能与表层浮游植物的光合作用有关。礁坪区POC及DOC都呈现显著的周日变化特征，POC呈现夜晚高，白天低的特点，浮游植物的昼夜垂直移动可能是产生该现象的主要原因。DOC的周日变化则主要受浮游动物昼夜垂直移动及细菌等生物活动的影响。

Distribution of dissolved organic carbon (DOC) in seawater of Zhubi Reef, Nansha Islands and diurnal changes of particulate organic carbon (POC) and dissolved organic carbon in reef flat were observed during April, 1999. It was shown that the content of DOC in surface water ranges from 1.43 to 3.62 mg/L, with an average of 2.16 mg/L. In different reef zones, DOC content showed much variation and the decrease order was reef flat > lagoon > outer waters. The vertical distribution of DOC in the lagoon showed a tendency of surface samples higher than deeper samples, which may be caused by higher photosynthesis of phytoplankton in surface. Both POC and DOC in a station on reef flat showed significant diurnal fluctuations. The diurnal change of POC was higher at night than in daytime, which was caused by diurnal migration of phytoplankton and demersal zooplankton while the main cause of diurnal changes of DOC may be diurnal migration of demersal zooplankton and bacteria activity.