In summer, the Madden-Julian Oscillation (MJO) greatly influences the intraseasonal variability of the South China Sea (SCS). Previous studies have revealed MJO effects on surface chlorophyll (Chl) concentration, but the impact of the MJO on the ecosystem's structure and functionality remains unexplored. Here, we investigated the marine ecosystem response to the MJO by analyzing phytoplankton pigment data collected in cruises from 2010 to 2014. The results indicated the strong influence of the MJO on the structure of phytoplankton size classes (PSCs) in the upper 50 m of the SCS basin. To further explore the ecosystem's response to MJO, we utilized a well-calibrated physical-biogeochemical model (ROMS-CoSiNE) of the SCS to conduct numerical experiments with and without MJO forcings. Our model demonstrated that MJO-induced deep mixing and upwelling increased nutrients in the upper layer, increasing the Chl concentration with a higher proportion of nanophytoplankton (15 %) and a lower proportion of picophytoplankton (−20 %). Moreover, The MJO-forced model experiment exhibited a substantial enhancement in primary production (56 %) and export production (23 %), resulting in a notable decrease in the e-ratio. This reduction in the e-ratio cannot be attributed to changes in PSCs but can be explained by the time lag between primary and export production. This lag was prolonged by the physical processes of upwelling and mixing, which slows down the particle sinking. Our results emphasize the important role of MJO in regulating the ecosystem at intraseasonal scale, thus improving our comprehension of the nonsteady dynamics of ecosystems in the SCS.

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南海海洋浮游生态系统对夏季马登-朱利安振荡的季节内响应：一项模型研究

夏季，马登-朱利安涛动（MJO）极大地影响了南海（SCS）的季节内变化。先前的研究揭示了 MJO 对表面叶绿素 (Chl) 浓度的影响，但 MJO 对生态系统结构和功能的影响仍未得到探索。在这里，我们通过分析 2010 年至 2014 年巡航中收集的浮游植物色素数据，研究了海洋生态系统对 MJO 的响应。结果表明，MJO 对 MJO 上部 50 m 的浮游植物尺寸等级（PSC）结构产生了强烈影响。南海盆地。为了进一步探索生态系统对 MJO 的响应，我们利用南海经过良好校准的物理生物地球化学模型 (ROMS-CoSiNE) 来进行有和没有 MJO 强迫的数值实验。我们的模型表明，MJO 引起的深度混合和上升流增加了上层的营养物质，增加了叶绿素浓度，其中纳米浮游植物的比例较高（15％），微型浮游植物的比例较低（−20％）。此外，MJO强制模型实验显示初级产量（56％）和出口产量（23％）显着提高，导致e比率显着下降。 e 比率的下降不能归因于 PSC 的变化，而是可以用初级生产和出口生产之间的时间滞后来解释。上升和混合的物理过程延长了这种滞后，从而减慢了颗粒下沉的速度。我们的研究结果强调了MJO在季节内尺度生态系统调节中的重要作用，从而提高了我们对南海生态系统非稳态动态的理解。