Summer phytoplankton blooms appear frequently off the Somali coast in the southwestern Arabian Sea (AS), where strong reversal monsoon and summer upwelling is prevailing. Distinct high chlorophyll-a (Chl-a) concentrations in summer were displayed in the western AS, especially in the region off the Somali coast. The spatial and inter-annual variations of the summer high Chl-a were studied using satellite data including ocean color and wind vectors. Under ocean conditions including monsoon winds, Ekman transport (ET) and Ekman pumping velocity (EPV), as well as geostrophic current and aerosol precipitation, the possible mechanisms of high Chl-a was investigated. The summer high Chl-a presented strong inter-annual variations in the southwestern AS. The results of simple correlation analysis indicated that there were good correlations between the ET and Chl-a, as well as between EPV and Chl-a. These implied that the ET and EPV may cause uplift of nutrients into the upper layer of the western AS from subsurface or coastal regions, inducing high Chl-a in the southwestern AS, especially in the region off the Somali coasts in summer. The multiple/partial correlation analysis implied further that EPV-induced upwelling may be more helpful than the ET-induced upwelling in the coastal region off Somalia, leading to probably more significant influence of EPV upwelling on the phytoplankton bloom than upwelling by ET. Aerosol precipitation in the southwestern AS also played an important role in high Chl-a in the deep offshore AS (i.e., Section B in Fig. 1(a)), as second only to ET and sea surface temperature (SST), and even higher than EPV. A novel finding is that the influence of aerosol optical thickness (AOT) is evident in the offshore region and the dust precipitation is more importantsources to oligotrophic water. Both the stability of the upper ocean and the aerosol precipitation may play more evident roles in the open regions of the southwestern AS off Somali.

夏季浮游植物大量出现在阿拉伯海 (AS) 西南部的索马里海岸附近，那里盛行强烈的逆转季风和夏季上升流。独特的高叶绿素a（Chl-一夏）浓度显示在西方，尤其是在该地区在索马里海岸。夏季的空间和年际变化高Chl-一个使用卫星数据，包括海洋的颜色和风矢量进行了研究。在包括季风、埃克曼输运 (ET) 和埃克曼泵速 (EPV) 以及地转流和气溶胶降水在内的海洋条件下，研究了高 Chl- a的可能机制。夏季高叶绿素a在 AS 西南部呈现出强烈的年际变化。简单相关分析结果表明，ET与Chl- a、EPV与Chl- a之间存在良好的相关性。这意味着 ET 和 EPV 可能导致营养物质从地下或沿海地区抬升到西部 AS 上层，导致高 Chl- a在 AS 西南部，尤其是夏季索马里沿海地区。多重/偏相关分析进一步表明，在索马里沿海地区，EPV 诱导的上升流可能比 ET 诱导的上升流更有帮助，导致 EPV 上升流对浮游植物水华的影响可能比 ET 上升流更显着。AS 西南部的气溶胶降水也对高 Chl- a起重要作用。在深海AS（即图1（a）中的B部分）中，仅次于ET和海面温度（SST），甚至高于EPV。一个新的发现是，近海地区气溶胶光学厚度（AOT）的影响明显，沙尘降水是贫营养水的重要来源。上层海洋的稳定性和气溶胶降水可能在索马里海域西南 AS 的开阔地区发挥更明显的作用。