Mesoscale warm-core eddies are common in the Bay of Bengal (BoB), and this study in the western BoB during Pre-Southwest Monsoon (April 2015) presents how a prolonged warm-core core eddy could modify the microplankton biomass and size structure. To investigate this, field sampling and laboratory analyses were augmented with satellite data sets of sea surface temperature (SST), winds, mean sea level anomaly (MSLA), geostrophic currents and chlorophyll-a. High SST with positive MSLA (≥ 20 cm) and a clockwise circulation, represented the occurrence of a large warm-core eddy in the western BoB. Time series data evidenced that it was originated in the mid of March and persistent there till early June, which in turn caused a decrease in the surface nutrients and chlorophyll-a. The abundance and biomass of microplankton were negligible in the warm-core eddy region. FlowCAM data showed a significant decrease in the autotrophic microplankton parameters in the warm-core eddy (av. 13 ± 9 ind. L⁻¹ and 0.1 ± 0.04 µgC L⁻¹, respectively) as compared to the surrounding locations (av. 227 ± 143 ind. L⁻¹ and 0.8 ± 0.5 µgC L⁻¹, respectively). Low nutrients level in the warm core eddy region favoured high abundance of needle-shaped phytoplankton cells dominated by Trichodesmium cells. As a result, the size of micro-autotrophs in the warm-core eddy was larger (av. 91,760 ± 12,902 µm³ ind.⁻¹) than its outside (av. 50,115 ± 21,578 µm³ ind.⁻¹). This is a deviation from our belief that the oligotrophy decreases the phytoplankton size. We showed here that the above understanding might not be infallible in warm-core eddies in the northern Indian Ocean due to its inducing effect on the Trichodesmium abundance.

中尺度暖核涡流在孟加拉湾 (BoB) 中很常见，这项在西南季风前 (2015 年 4 月) 期间在 BoB 西部进行的研究展示了长时间的暖核涡流如何改变微型浮游生物的生物量和大小结构。为了对此进行调查，现场采样和实验室分析增加了海面温度 (SST)、风、平均海平面异常 (MSLA)、地转洋流和叶绿素a 的卫星数据集。具有正 MSLA (≥ 20 cm) 和顺时针环流的高 SST 代表在 BoB 西部发生了大的暖核涡流。时间序列数据表明，它起源于 3 月中旬并持续到 6 月初，这反过来又导致地表养分和叶绿素a的减少。. 暖核涡区微浮游生物的丰度和生物量可以忽略不计。FlowCAM 数据显示，与周围位置 (av. 227 ± 分别) 相比，暖核涡流中的自养微浮游生物参数显着降低 (av. 13 ± 9 ind. L ^-1和 0.1 ± 0.04 µgC L ^-1 ) 143 ind. L ^-1和 0.8 ± 0.5 µgCL ^-1）。在暖心涡区营养成分低级别的青睐高丰度为主的针形浮游植物细胞的红海束毛细胞。因此，暖核涡流中的微型自养生物的尺寸 (av. 91,760 ± 12,902 µm ³ ind. ^-1 ) 大于其外部 (av. 50,115 ± 21,578 µm)³ IND。^-1 )。这与我们认为寡营养减少浮游植物大小的信念背道而驰。我们在此表明​​，由于其对Trichodesmium丰度的诱导作用，上述理解在北印度洋的暖核涡流中可能不是绝对正确的。