南海是著名的寡营养盐低生产力区, 同时也是热带气旋频发的海域, 强的热带气旋通常会给海洋上层带来强烈的扰动, 可能引起营养盐的卷入并引起海洋上层浮游植物的急剧增加。由于移动速度较快的弱台风及热带气旋对深水海域生态系统的影响通常较为有限, 以往相关的研究通常关注强度较强、移动较慢的台风对深水海区生态系统的影响。文章研究了一个强度较弱、移动较快的跨陆架区热带风暴“天鹰”对陆架区浮游植物的影响, 通过对比强风事件前后风场及背景环境要素的变化特征, 探讨了这种弱热带气旋事件对陆架区海洋浮游植物的可能贡献。研究结果表明, 2005年7月“天鹰”形成前南海西北部夏季叶绿素浓度通常较低(<0.12mg·m-3), 气旋过境后浮游植物叶绿素浓度显著增加(>0.14mg·m-3), 平均大约增加33%。这种叶绿素浓度短期迅速增加与同期风场的变化有关。对强风事件期间垂向温度、声学多普勒海流剖面(ADCP)数据以及营养盐水平分布的分析表明, 短暂的强风事件在营养盐跃层较浅的陆架区能导致较强的卷吸混合及惯性振荡流, 诱发生源物质由下至上的输送, 以及风暴引起的强降水在有利流向作用下将营养物质由近到远的输运, 导致海南岛东南部海域浮游植物的迅速增加。
The water in the South China Sea (SCS) belongs to tropical oligotrophic type with low primary productivity. This SCS is frequently affected by tropical cyclones. Strong tropical cyclones can trigger violent disturbances in the upper ocean, bringing nutrients into the surface layer, which increases phytoplankton primary production. Due to limited influence of fast-moving, weak cyclones on offshore deep waters and related marine ecosystems, previous studies focused generally on contribution of strong or slow-moving typhoons on marine ecosystems in the SCS. The present study analyzes increase in chlorophyll after a fast-moving, weak tropical storm in the continental shelf, investigating possible influence of a short-lived tropical storm using wind, currents, and other oceanographic data on phytoplankton over continental shelf. The results indicate the generally low chlorophyll-a (<0.1 mg·m-3) in the continental region of the western SCS east of Hainan province before the storm, and more than 30% increase of chlorophyll-a (>0.14 mg·m-3) after the storm. The prominent increase of chlorophyll-a may be associated with the tropical storm. Analyses of vertical CTD (conductivity-temperature-depth recorder) temperature profiles and ADCP (acoustic Doppler current profilers) current profiles imply that the storm can induce strong inertial oscillation and precipitation as well as mixing/entrainment, together with tide influences, trigger uptake of nutrients and support increase of chlorophyll-a. In addition, comparing with deep seas, the relative shallow nitracline in continental shelf regions is also favorable to upwelling of nutrients.
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